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CHAPTER

6
Single-Ply Roofing

T he single-ply membrane roofing system was developed in Europe in

the late 1950s, partially in response to difficulties in obtaining
asphaltic materials for conventional roofing systems. Single-ply mem-
branes were first introduced in the United States in the mid-1960s by
European manufacturers. Since their first appearance in our country,
single-ply materials have become increasingly popular. Whether
imported from Europe or produced domestically, these products have
proven themselves in a wide variety of climates over more than four
decades of use.
Built-up roofs (BUR) are literally constructed on the roof by the
contractor, using component materials such as felts and asphalt (Fig.
6-1). Thus, they are subject to problems caused by weather, worker
error, and material inconsistencies. Single-ply membranes, however,
are flexible sheets of compounded synthetic materials that are manu-
factured in a factory to strict quality control requirements. This
process minimizes the risks inherent in BUR systems.
Primary among the many physical and performance properties
that these materials provide are strength, flexibility, and long-lasting
durability. The prefabricated sheets are inherently flexible, can be
used with a variety of attachment methods, and are compounded to
provide watertight integrity for years of life. These various factors are

135
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136 CHAPTER SIX

F I G U R E 6 - 1 A single-ply installation.

the reason for the popularity of single-ply systems, which account for
up to 40 percent of the commercial roofing market.
There are many different single-ply roofing products. Although
their chemistry and composition are complex, the Single-Ply Roofing
Institute (SPRI) classifies them into three main groups: thermosets,
thermoplastics, and modified bitumens. Each of these types of single-
ply membranes includes of a number of individual products.

Casting Thermosets
Single-ply thermoset materials are chemical crosslinkages of polymer
that cannot be changed once the sheet material is cast. Two types of
thermosets are used for roofing: vulcanized, or cured, elastomer and
nonvulcanized, or noncured, elastomer.
The advantages associated with elastomeric roofing include perfor-
mance, cost benefits, conservation, the substitution of materials, and
adaptability to a wide range of roof configurations. The membrane is
able to elongate and accommodate movement in the substrate. The
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SINGLE-PLY ROOFING
137
extension or elongation of certain systems at room temperature can be
as high as 700 to 800 percent. Elastomeric membranes can bridge non-
working joints and cracks in the substrate without cracking and split-
ting, provided they are not bonded or are reinforced at these locations.
The ability of the membrane to remain flexible at low temperatures
is another feature. Some elastomeric membranes remain flexible at
temperatures as low as –50°F, whereas conventional bituminous mem-
branes become brittle within a range of about 0° to 45°F. Some elas-
tomeric membranes retain their ability to elongate at low temperatures,
although the elongation is reduced from that at room temperature, or
approximately 68°F.
Some elastomeric roofing systems weigh less than 10 pounds per
100 square feet of roof area. This is a minimal weight when compared
to that of smooth-surfaced bituminous systems, which weigh approxi-
mately 150 pounds per square foot.
Roof designs for many modern buildings must be architecturally
attractive and functional. These roofs include a variety of configurations,
such as domes, barrels, and hyperbolic paraboloids. Conventional mate-
rials usually are not suitable for these shapes. Elastomeric membranes
are able to conform to a variety of shapes and contours. This makes them
suitable roofing materials for these modern architectural designs.
In addition, some elastomeric roof membranes are available in a
variety of colors that can enhance the attractiveness of roofs. Colors
can also be reflective, which reduces the absorption of solar radiation
and results in lower roof temperatures.

Vulcanized Elastomers
Ethylene propylene diene terpolymer (EPDM) and chlorinated poly-
ethylene (CPE) are the two most popular vulcanized elastomers.

ETHYLENE PROPYLENE DIENE TERPOLYMER (EPDM)

This thermoset membrane is compounded from rubber polymer and is
often referred to as rubber roofing. The American Society for Testing
and Materials (ASTM) classifies this material as an M class polymer.
The M in EPDM is sometimes taken to mean monomer, which is tech-
nically incorrect.
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138 CHAPTER SIX

Ethylene and propylene, derived from oil and natural gas, are the
organic building blocks of EPDM. When these are combined with
diene to form the basic rubber matrix, the result is a long-chain hydro-
carbon with a backbone of saturated molecules and pendant double
bonds. The practical translation is that ethylene, propylene, and diene
combine to form a large molecule that is very stable when exposed to
sunlight, heat, ozone, and moisture.
These molecules can be cured, or vulcanized, into a rubber sheet
that permits elongation of more than 400 percent without structural
damage. In other words, EPDM is the binder material, or the basic rub-
ber matrix that gives the final membrane rubber properties. Carbon
black, oils, processing aids, and curatives are added to increase tensile
strength, flexibility, mixing, and dimensional stability.
Features that contribute to the popularity of EPDM single-ply
roofing systems include:

■ Long-term weatherability, including excellent resistance to tem-

perature extremes, sunlight, ozone, and moisture
■ Ease, speed, and cleanliness of installation

■ Flexural stability; an elongation factor enables EPDM membranes

to accommodate roof deck movement and displacement
■ Compatibility with a wider variety of polystyrene insulation
products than asphaltic materials
■ Ease of maintenance

■ Proven long-term performance

Another feature is adaptability. Various application techniques,

such as ballasted, fully adhered, and mechanically fastened, allow
EPDM roofing systems to be applied to virtually any roof surface: flat,
spherical, curved, or slanted.
EPDM also offers reroofing flexibility. When the roof deck is
moisture-free, EPDM can be installed over existing roof membranes
in reroof situations. Finally, code and standardization progress by
the Rubber Manufacturers Association (RMA), Underwriters’ Labo-
ratories, Inc. (UL), and Factory Mutual (FM) contribute to the
demand.
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SINGLE-PLY ROOFING
139
Ballasted: Ballasted systems are the most common for rubber-based,
single-ply roofs. The thermal insulation and rubber membrane are
loosely laid over the roof deck and then covered with ballast, which
is usually round, washed river rock as specified by ASTM. The
major advantages of this method include low installation costs, ease
of installation, a UL Class A fire rating, and separation of the mem-
brane from the deck, which allows for maximum independent
movement.

Fully Adhered: This is the second most popular application method

(Fig. 6-2). Ideal for contoured roofs, sloped surfaces that cannot with-
stand the weight of a ballasted system, or reroofing applications over
existing material, fully adhered membranes are completely bonded
to the substrate using contact adhesives. Major advantages include
their light weight, durability, ease of maintenance, and aesthetically
clean, smooth appearance.

F I G U R E 6 - 2 Apply adhesive on a fully adhered EPDM roof.

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140 CHAPTER SIX

Mechanically Fastened: With this method, the membrane is loosely

laid over the substrate and then anchored to the deck using fasteners.
Many types of mechanically fastened systems are available. Most com-
mon are those attached directly to the deck. Nonpenetrating systems
are also available. Mechanically fastened systems are lightweight, easy
to install, and relatively inexpensive. As discussed later in this chap-
ter, a recent development in EPDM is a sheet that can be heat welded.

CHLORINATED POLYETHYLENE (CPE)

CPE exhibits properties of both vulcanized and nonvulcanized elas-
tomers. CPE is manufactured as a thermoplastic, but over time it cures
as a thermoset. This means that most CPE systems are typically hot-air-
or solvent-welded. The features and benefits of CPE are discussed in
greater detail in the nonvulcanized, uncured elastomers section.

Polychloroprene or Neoprene
Neoprene is a generic name for polymers of chloroprene. It was the
first commercially produced synthetic rubber and exhibits resistance
to petroleum oils, solvents, heat, and weathering. It is available in
sheet and liquid-applied forms, and in weathering and nonweathering
grades. Weathering grade is black; nonweathering is light-colored.
Nonweathering grade must be protected from sunlight, normally by
applying a coating of usually chlorinated polyethylene. Neoprene for-
mulations are no longer widely used for roofing.

Nonvulcanized, Uncured Elastomers

The manufacturing process differentiates these uncured elastomeric
membranes from vulcanized polymers. During the production of vul-
canized polymers, combinations of chemicals, primarily polymers,
fillers, and additives, are processed together and cured by heating so
that chains of molecules are permanently crosslinked.
This curing method results in a thermoset membrane with low ten-
sile strength and high elongation values. In the field, cured elastomers
must be applied and repaired with adhesives. New chemical bonds
cannot be formed.
Nonvulcanized, uncured elastomers, in contrast, are manufactured
without any crosslinks between chains of polymer molecules. Although
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SINGLE-PLY ROOFING
141
exposure to the elements can naturally cure some of these polymers
during their lifespan, all nonvulcanized elastomers can be heat-welded
during the initial installation.
The generic classification of polymers known as nonvulcanized
elastomers includes chlorosulfoned polyethylene (CSPE), chlorinated
polyethylene (CPE), polyisobutylene (PIB), and nitrile alloy with
butadiene-acrylonitrile copolymers (NBP).

CHLOROSULFONED POLYETHYLENE (CSPE)

CSPE, sold under the DuPont trademark Hypalon, is a polymer that
has enjoyed increased popularity over the years because of its attrac-
tive white appearance and energy-efficient, heat-reflective properties.
Other factors contributing to the popularity of CSPE and other rubber-
based, single-ply roofing systems include

■ Long-term weatherability; excellent resistance to temperature

extremes, sunlight, ozone, and moisture
■ Ease, speed, and cleanliness of installation

■ Reduced labor costs in many cases

■ Flexural stability; accommodation of deck movement and dis-

placement
■ Routine reroof installation over existing moisture-free mem-
branes
■ Compatibility with many insulation materials

■ Code and standardization progress by the RMA and others

■ Ease of maintenance

■ Proven long-term performance

Another benefit is adaptability. Application techniques allow

rubber-based roofing systems to be applied to virtually any roof sur-
face: flat, spherical, curved, or slanted.
CSPE is a saturated polymer that contains chlorine and sulfonyl
chloride groups attached to a polyethylene backbone. It is an elas-
tomeric material. Typical elongations range from 200 to 400 percent,
depending on the type and amount of reinforcing fillers present in the
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142 CHAPTER SIX

compound. This means that CSPE can stretch far beyond its original
length and return to its original configuration without loss of struc-
tural integrity.
Actually, a unique feature of CSPE is that it is manufactured as a
thermoplastic, but over time it cures as a thermoset. This means that
most CSPE systems are typically hot-air- or solvent-welded. The
advantages of welded seams include relatively quick procedures, good
strength, and the lack of additional seaming material. There are two
primary methods of application for CSPE rubber-based, single-ply sys-
tems, each of which offers certain advantages in specific applications.

Mechanically fastened. The membrane is loosely laid over the sub-

strate and then anchored to the deck using fasteners. Many types of
mechanically fastened systems are available. The most common
are those that attach directly to the deck. Nonpenetrating systems
also are available. Advantages include the fact that the systems are
lightweight, easy to install, and relatively inexpensive.
Fully adhered. Ideal for contoured roofs or sloped surfaces that can-
not withstand the weight of a ballasted system, fully adhered mem-
branes are completely bonded to the substrate with contact
adhesives. The major advantages include the fact that these sys-
tems are lightweight, durable, and easy to maintain. They also have
an aesthetically clean and smooth appearance.

Only a handful of CSPE systems are installed using the ballasted

technique popular with other rubber-based roofing systems because
most building owners prefer not to cover the attractive white mem-
brane. In fact, CSPE systems are often specified because of their attrac-
tive white exterior.

CHLORINATED POLYETHYLENE (CPE)

This material is formulated around its prime polymers and blended
with pigment and processing aids, which serve as release agents and
antioxidants. In fact, one manufacturer produces 15 grades of cured
and uncured raw CPE polymer.
CPE made its roofing debut in 1967. Prior to that, it emerged in var-
ious military and civilian applications, most notably as a pond liner.
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SINGLE-PLY ROOFING
143
The majority of today’s CPE roof membranes are offered in an uncured
composition and are reinforced with a polyester scrim by individual
roofing manufacturers. Standard thicknesses are 40 to 48 mils. Both
CPE and CSPE normally are formulated without plasticizers because
of their inherent flexibility as an elastomer.
As closely related elastomers, CSPE and CPE share similar behav-
ioral characteristics. An aged CSPE, however, cannot be heat-welded.
Adhesives must be applied if field repairs are necessary. The methods
of application are the same for CPE and CSPE.

POLYISOBUTYLENE (PIB)
PIB is usually a 60-mil membrane made from synthetic rubber poly-
mer, or polyisobutylene, pigments, fillers, and processing aids
within several quality-control parameters that relate to thickness,
density, elongation, hardness, and so on. The underside of the mem-
brane is generally laminated with a 40-mil, needle-punched, non-
woven, rot-proof polyester fabric. The membrane is finished with a
2-inch-wide, self-sealing edge material that is protected by a strip of
release paper.
PIB is compatible with hot asphalt and shows excellent resistance
to weathering, radiant heat, and ultraviolet (UV) light. Used primarily
as a final waterproofing membrane over existing flat or low-sloped
roof assemblies, PIB can also be used as a waterproofing membrane for
new-construction roof assemblies.
PIB is a lightweight system that requires no ballast. It can be
installed quickly and economically. PIB passes UL’s Class A fire rating
and FM’s I-90 wind-resistance rating.
These systems offer both the building owner and the roofing con-
tractor numerous advantages. The self-sealing edge offers assured
seam strength, long-term waterproofing, lower installation costs, faster
application per worker hour, and no need for special capital equip-
ment. The fact that the system is unballasted can eliminate the need to
structurally reinforce the building before it is reroofed. PIB also mini-
mizes the deck load and eliminates the logistics of adding 1000 to
1200 pounds of gravel for every 10-foot-square area.
PIB has a short but successful history in the United States. As more
people become familiar with the system, realize that it is a solution for
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144 CHAPTER SIX

many roofing problems, and view the evidence of product support and
longevity, the PIB system continues to show steady growth in the sin-
gle-ply market.

NITRILE ALLOYS (NBP)

These membranes, as thermoset elastometers, are compounded from
butadiene-acrylonitrile copolymers, nonvolatile polymeric plasticiz-
ers, and other patented ingredients.
These membranes typically are made by coating the compound on
a heavy-duty polyester fabric. They range in thickness from 30 to 40
mils. Seams are hot-air welded. Used for almost 30 years for such
diverse products as exterior door gaskets and footwear, NPB is recog-
nized for its weather-protectant and waterproofing capabilities. The
material exhibits good chemical resistance and low-temperature flexi-
bility, but is sensitive to aromatic hydrocarbons.

Heating Thermoplastics
When heat is applied to a thermoplastic, its polymer chains slide
freely over one another. This makes the plastic more pliable and heat
weldable. When returned to ambient temperature, the polymer chains
again intertwine and regain their original properties. This process
can be repeated again and again with the same results, which
explains why seaming is so excellent and easily done with a thermo-
plastic.
Thermoplastic roofing systems tend to be lighter in color, which
can add value in terms of aesthetics. They are especially popular in
multitiered roofing that can be seen from above by building occupants
or neighbors.
The two most common chlorinated hydrocarbon thermoplastics are
polyvinyl chloride (PVC) and CPE.

Polyvinyl Chloride (PVC)

PVCs, originally produced in Germany more than 30 years ago, are
among the most versatile thermoplastics for industrial and commer-
cial applications. PVC is synthesized from vinyl chloride and is a
member of a larger group of polymers designated as vinyls. These poly-
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SINGLE-PLY ROOFING
145
mers are composed of intertwined molecular chains. This, in part, is
what gives PVC its unusually good physical properties.
PVC is one of the easiest materials to use. In its uncompounded state,
PVC is a rigid material. Historically, PVC has been used in residential
and commercial piping, plumbing, window frames, and exterior siding.
When blended with plasticizers, PVC becomes soft and pliable. The use
of the proper plasticizers enables membranes based on PVC to be used
over a wide temperature range without substantial change. Because PVC
is a plastic and not a rubber, it is unaffected by ozone.
Ingredients are added to PVC to protect the polymer during pro-
cessing and manufacture, or to achieve specific requirements such as
increased flame retardance, resistance to microbiological attack, and
resistance to UV light. PVC is an excellent choice when high perfor-
mance and economy of cost are the primary factors in roof selection.
PVC is forgiving. Installation mistakes can be easily corrected, and
alterations, such as the addition of air-conditioning systems at a later
date, are easily accomplished. For this reason, PVC conforms to non-
standard details with exceptional ease. With regard to seam integrity,
thermoplastic roofing membranes can be welded together with heat or
solvents. Once welded, they develop bond strengths that equal or sur-
pass the strength of the base material.
PVC membranes can be installed by three different methods:
loose-laid, partial bonding, and fully adhered. The simplest installa-
tion procedure is to loosely lay the material on the substrate. Attach
the membrane only around the perimeter of the roof and at any pene-
trations. The insulation does not need to be fastened in place, as the
roofing system is ballasted to resist wind uplift. Since the membrane
is not attached to the substrate, stresses in the substrate are not trans-
ferred to the membrane. Gravel ballast must be of sufficient size and
free of sharp edges, so that it does not puncture the membrane.
The partial bonding method uses elements of both the loose-laid
and fully adhered systems. Firmly fasten insulation material beneath
the membrane to the substrate. Then mechanically fasten round
plates firmly to the substrate in a predetermined pattern and spacing.
Finally, bond the membrane to the pattern. Partial bonding allows
the membrane to float free over a crack or joint in the substrate. This
distributes stress in the membrane between adhered areas. It is not
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146 CHAPTER SIX

intended to serve as or replace an expansion joint. On partially

adhered systems, there are voids between membranes and substrates.
If moisture enters the void and vapor pressure builds, blistering can
occur.
The fully adhered method completely fastens the roofing system to
the roof deck. For sheet systems, total bonding is usually achieved by
applying an adhesive. The substrate for adhesive-bonded systems
must be smooth, clean, dry, and free from dust, dirt, grease, oil, wax,
and loose particles. Many manufacturers recommend that the sub-
strate be primed before adhesive is applied to achieve greater bond.
Contact adhesives are typically used in total bonding. They are
applied to the top surface of the substrate and the bottom of the sheet.
Some sheets are self-adhering, however, so that the bottom of the sheet
adheres to the substrate without an adhesive.
The fully adhered method is suited to reroofing projects when the
old roofing is not removed. It can also be used on steep roofs that can-
not contain ballast and where partial bonding allows the membrane to
sag between fastening points. Mechanically fasten a layer of hardboard
or insulation to the deck, since PVC is incompatible with asphalt or
coal tar.
The system designer must consider all roofing materials when spec-
ifying PVC. Common roof materials like asphalt and coal-tar pitch can-
not come in contact with PVC single-ply roofing. If they do, the PVC
membrane may fail. All PVC roofing manufacturers stress that the
membrane must be completely isolated from any contact with bitumi-
nous materials. Even fumes from coal tar must be avoided. Bituminous
materials have the effect of leaching the plasticizers out of the PVC,
leaving it weak and brittle.
Polystyrene insulation must not come in direct contact with
PVC, since it can rapidly extract the plasticizers from the mem-
brane. The treatment used for wooden blocking and nailers must be
carefully considered because only waterborne wood preservatives
can be used.

Chlorinated Polyethylene (CPE)

Thermoplastic elastomers, such as CPE, are unique in that they have
elastomeric properties, have rubber-like elasticity, and are easy to
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SINGLE-PLY ROOFING
147
install, like PVC. In fact, CPE can be applied in the same manner as
PVC. Welds can be made with heat or solvent and detailing is accom-
plished easily because of the thermoplastic-like properties of CPE.
With noncuring elastomers, such as CPE, the chemical properties
are such that the polymer chains are designed not to crosslink during
the material’s useful lifetime. Such a material has most of the desirable
performance properties of a true rubber and easily conforms to any
subsequent alteration to the roof. Such membranes seam almost as eas-
ily after being in place several years as when they were initially
installed. Noncuring elastomers exhibit a mix of the qualities of both
rubber and thermoplastic.
CPE resin in a pure form offers a soft membrane with poor physical
properties. In order to be used as a roofing material, CPE polymer must
be enhanced with other reinforcing chemicals, such as processing aids
that ease polymer processing and stabilizer packages that protect and
enhance the polymer when it is installed on the roof.
CPE offers the best chemical resistance of any conventionally avail-
able, single-ply roofing material. Depending on the given application,
CPE is resistant to acetic acid, asphalt, bleach, chlorine, coal tar, fuel
oils, animal fats and oils, fertilizer, sulfuric acid (acid rain), and a
broad range of other corrosives. An excellent all-around choice as a
roofing membrane, CPE has superior resistance to weathering, UV
radiation, ozone, and microbiological attack. In addition, CPE has
good fire resistance qualities.

Featuring Modified Bitumen Roofing

Modified bituminous roofing (MBR) systems have their technical roots
in Italy, France, and Germany. They first appeared on the American
market in 1975. Consisting of asphalt, a conventional base material, and
any one of a number of polymeric modifiers, MBR membranes bridge
the gap between conventional hot-applied BUR and nonconventional
single-ply membranes.
MBR systems cover the full range of inplace system specifications.
These systems currently are being applied using loose-laid, partially
attached, and totally adhered methods, and as protected membrane
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148 CHAPTER SIX

systems. In addition, MBRs can be applied over a wide range of roof

decks and roof insulations.
The requirements for deck selection, roof insulation, vapor retarder
application, drainage, and flashing details that apply to conventional
hot-BUR applications are generally applicable to most MBR systems as
well. This makes the selection of an MBR system particularly attrac-
tive to the roofing contractor who might be skeptical of other single-
ply systems’ application requirements and techniques.
The MBR system is also versatile in its application method. These
systems can be applied by hot-asphalt application, heat-welding or
torching, or cold adhesive. Some systems have self-adhering proper-
ties. Again, this versatility provides the roofing contractor with a wide
range of application choices that can be tailored to specific job require-
ments.
The MBR membrane is similar to hot-BUR systems, but represents a
refinement in conventional asphalt technology. Though both systems
have distinct softening points and proper installation temperatures,
MBRs are composite sheets modified by either plastic or elastomeric
material, such as atactic polypropylene (APP), styrene block copolymer
(SBC), styrene-butadiene-styrene (SBS), or styrene-butadiene-rubber
(SBR).
Both the SBR-modified and APP-modified bitumen systems pro-
duce good lap-joint strength. Lap-joint construction for the APP-
modified membranes normally is accomplished by torching. SBR- and
SBS-modified membranes normally are adhered using hot asphalt as
the adhesive. They also can be torched, although the APP-modified
systems are more conducive to torching. The APP modification allows
the bitumen material to flow easily when heat is applied directly, thus
the term torching felt.
Like BUR membranes, the MBR membrane consists of layers of
modified asphalt that waterproof a reinforcing material. The reinforc-
ing in MBR might be glass-fiber mats, polyester scrim, or a combina-
tion of the two. Each type of reinforcing material imparts different
properties to the membrane. The manufacturing process usually dic-
tates the location of the reinforcing material within the membrane.
Membranes with reinforcing material sandwiched in the center are
the easiest to fabricate. Properties of the reinforcement material, how-
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SINGLE-PLY ROOFING
149
ever, also affect its location. Because polyester is not UV resistant, it
must be buried in the mat, but not too close to the bottom because heat
causes it to shrink and melt. Glass-fiber reinforcement material gener-
ally is placed close to the top of the mat to serve as a wearing surface.
It resists foot traffic and UV degradation and provides a fire rating. One
argument against this location is the potential for delamination during
application.
Manufacturers using both types of reinforcement put the glass fiber
at the top and the polyester in the middle. Roofing contractors like
reinforcement in the middle because the top melts slightly when the
next layer is applied, which fuses it to the bottom of the layer above.
MBR membranes range in thickness from 40 to 60 mils.
Some MBR membranes are best covered. For example, SBS must be
covered at all times because its UV and ozone resistance is low. Most
surfacing consists of granules provided by the manufacturer. This
granule surfacing does not add much weight to a system. Other cover-
ings include manufacturer-installed metals or applied coatings of
acrylics, asphalt emulsions, or fibrated aluminum. Of these, fibrated
aluminum is the most popular because of its reflective properties. The
differential movement of metal applied over asphalt is solved by fabri-
cating tiny expansion joints into the metal.
UV-resistant APP can be left uncoated. It usually is coated, how-
ever, to promote longer life. Coatings include fibrated aluminum,
acrylics, and asphalt emulsions. Mineral surfacings are available, too,
but generally are used only for their aesthetic effect. Surfacings also
are used to achieve fire ratings because most systems, with the notable
exception of glass-fiber-reinforced membranes, cannot attain a fire rat-
ing alone.
MBR systems generally are applied in either a single-ply or multi-ply
application (Fig. 6-3), frequently using conventional organic or fiberglass
felts as the base ply. Currently, the heat welding and hot-asphalt mop-
ping application methods seem to enjoy the most prominence.
MBR systems are suitable for application in new construction as
well as reroofing jobs. Because of their superior load-elongation
behavior, MBRs are frequently applied directly over existing conven-
tional roofing materials. This is possible only if the existing substrate
is not badly deteriorated or heavily moisture laden.
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150 CHAPTER SIX

4" lap
Nailable deck Nails
sheathing paper
(if required)

18"

37"
Felt
11"

3" lap Endlaps staggered

Drainage

Asphalt 3" apart (min)

36"
11"

4" endlap
9"
37"

3" lap
24"

Asphalt
18"

9"

Felt
F I G U R E 6 - 3 MBR can be applied with multiple sheets.

Preparing the Roof

The following are some general guidelines for the care and use of sin-
gle-ply membrane materials. (See also Fig. 6-4.)

■ Deliver materials in the manufacturer’s original unopened pack-

aging with labels intact.
■ Store materials onsite under protective coverings and off the
ground.
■ Do not store material on the deck in concentrations that impose
excessive strain on the deck or structural members.
■ Proceed with roofing work only when existing and forecasted
weather conditions permit installation in accordance with the
manufacturer’s recommendations and warranty requirements.
■ Take special precautions, as recommended by the manufacturer,
when applying roofing at temperatures below 40°F.
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✓ Item
Deliver materials in the manufacturer’s original
unopened packaging with labels intact.
Store materials onsite under protective coverings and
off the ground.
Do not store material on the deck in concentrations that
impose excessive strain on the deck or structural
members.
Proceed with roofing work only when existing and fore-
casted weather conditions permit installation in accord-
ance with the manufacturer’s recommendations and
warranty requirements.
Take special precautions, as recommended by the manu-
facturer, when applying roofing at temperatures below
40°F.
Do not torch-fuse membranes directly to flammable
substrates.
Check with the manufacturer about application require-
ments.
Check with the manufacturer about slope requirements.
The National Roofing Contractors Association (NRCA)
recommends that all roofing materials be installed on
roofs with positive slope to drainage.
If UL-classified roofing membranes are required, care-
fully evaluate the manufacturer’s test data to determine
compliance with code or other fire-related performance
characteristics.
Ensure that edge nailers, curbs, and penetrations,
including drain bases, are in place and properly secured
before starting the job so that the roof system can be
installed as continuously as possible.
Ensure that the insulation or base ply is positively
attached to the roof deck.

F I G U R E 6 - 4 Preparing the roof.

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152 CHAPTER SIX

✓ Item
Ensure that the bonding agent used to assemble laps
and to adhere the single-ply membrane to the roof sub-
strate is permitted by and acceptable to the material
supplier.
Ensure that positive attachment is achieved with par-
tially adhered and mechanically fastened MBR systems
that preclude a continuous film.
Ensure that the roof membrane is applied in such a way
that water can run over, or that the membrane has side-
laps and/or endlaps.
Check that sheets are aligned so that minimum required
end- and sidelap widths are maintained.
Check that membrane laps are watertight. Repair voids
and fishmouths within the lap as soon as possible.
Install temporary water cutoffs at the end of each day’s
work. Remove them before installing additional insula-
tion or membrane.
Apply surfacings, when required, in accordance with
the membrane supplier’s requirements and so that the
entire membrane surface is covered.

F I G U R E 6 - 4 (Continued)
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SINGLE-PLY ROOFING
153
■ Do not torch-fuse membranes directly to flammable substrates.

■ Check with the manufacturer about application requirements.

■ Check with the manufacturer about slope requirements.

■ The National Roofing Contractors Association (NRCA) recom-

mends that all roofing materials be installed on roofs with positive
slope to drainage.
■ If UL-classified roofing membranes are required, carefully
evaluate the manufacturer’s test data to determine compliance
with code or other fire-related performance characteristics.
■ Ensure that edge nailers, curbs, and penetrations, including drain
bases, are in place and properly secured before starting the job so
that the roof system can be installed as continuously as possible.
■ Ensure that the insulation or base ply is positively attached to
the roof deck.
■ Ensure that the bonding agent used to assemble laps and to
adhere the single-ply membrane to the roof substrate is permit-
ted by and acceptable to the material supplier.
■ Ensure that positive attachment is achieved with partially
adhered and mechanically fastened MBR systems that preclude
a continuous film.
■ Ensure that the roof membrane is applied in such a way that
water can run over, or that the membrane has sidelaps and/or
endlaps.
■ Check that sheets are aligned so that minimum required end-
and sidelap widths are maintained.
■ Check that membrane laps are watertight. Repair voids and fish-
mouths within the lap as soon as possible.
■ Install temporary water cutoffs at the end of each day’s work.
Remove them before installing additional insulation or mem-
brane.
■ Apply surfacings, when required, in accordance with the mem-
brane supplier’s requirements and so that the entire membrane
surface is covered.
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154 CHAPTER SIX

Applying Substrate Materials

Suggested substrate materials for MBR systems include light steel,
which does not have the weight of gravel or ballast; primed concrete,
which requires torch welding, particularly when not insulated;
mechanically fastened base sheets; and uninsulated assemblies when
the deck is wood, gypsum, lightweight insulating concrete, or cemen-
titious wood fiber.
MBR is not recommended for roofs where there are concentra-
tions of acids, hydrocarbons, or oils. It also is not cost effective for
wide-open spaces because large rolls of EPDM can be installed less
expensively.
The condition of the substrate is crucial to the performance of the
membrane. The surface of the deck must be clean, firm, smooth, and vis-
ibly and sufficiently dry for proper application. There are different
preparation requirements for new construction, replacement, or recov-
ering over each type of substrate. To avoid defects and litigation, the
material supplier and the roofing contractor can be responsible only for
acceptance of the surface of the substrate that is to receive the roofing
system. Design considerations and questions about structural sound-
ness are the responsibility of the owner or the owner’s representative.
Put this in the contract.
If there is a question about the suitability of the deck and/or its
surface, reach an agreement with the material supplier, the roofing
contractor, and the owner before proceeding with the work.
When a primer is required, coat the surface with an amount suffi-
cient to cover the entire surface. The amount required varies,
depending on the nature of the surface. Allow the primer to dry
before the membrane is applied. If visual examination indicates defi-
ciencies in primer coverage, apply additional primer for complete
coverage and then allow it to dry before applying the membrane.
The existing roof surface must be suitable to receive a single-ply
membrane. Both the NRCA and the RMA recommend putting a
recover board over existing gravel-surfaced roofs before the membrane
system is applied. Remove loose and protruding aggregate by spud-
ding, vacuuming, or power brooming to achieve a firm, even surface to
receive the recover board.
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SINGLE-PLY ROOFING
155
When the existing roof is smooth or mineral-surfaced, refer to the
material supplier’s specifications. Some specifications permit fully
adhering by heat welding, hot mopping, or adhesives. Others require
base sheets over the existing roof, while still others permit spot mop-
ping, strip attachment, and/or mechanical fastening.

Laying Insulation
Manufacturing tolerances, dimensional stability, application vari-
ables, and the nature of insulation boards make it difficult to obtain
tightly butted joints. Some variance is expected, but the spacing
between insulation boards should range from no measurable space to
no more than 1⁄4 inch or the space specified by the material supplier.
Fill insulation gaps between adhered or mechanically fastened
insulation boards in excess of 1⁄4 inch with roof insulation. Reduce gaps
between loosely laid insulation boards by adjusting the boards or
adding insulation. If the insulation boards appear to be out of square,
make a diagonal measurement to confirm the squareness. Do not use
defective material.
When composite-board, polyisocyanurate foam-board, polyure-
thane foam-board, perlitic board, or wood fiber-board insulation is
used as the insulation substrate under a torch-applied MBR membrane,
install a base sheet as the first layer below the roof membrane. This pro-
tects the insulation substrate from the flame and heat of the torch. Lap
each base sheet a minimum of 2 inches over the preceding sheet; end-
laps should be a minimum of 4 inches. Adhere the base sheets to the
insulation in accordance with the manufacturer’s specifications.

Fastening Insulation and Base Plies

Various mechanical fasteners are used to apply insulation and base
plies. They also can be used to attach the single-ply membrane to the
roof deck and to attach flashing materials. The fasteners often are spec-
ified by type, number, and spacing distance to fulfill the attachment
functions. Practical considerations often prevent exact spacing, such
as 6 inches on center. Reasonable variances from specified spacing dis-
tances are expected, but the minimum number of fasteners specified
should be used.
Scharff_Chap6_6x9-GOOD 9/21/00 10:44 AM Page 156

156 CHAPTER SIX

The fastener type and spacing should be as specified by the mater-

ial supplier with the understanding that the spacings are average val-
ues and the spacing between any two fasteners can vary. Should
fastener deficiencies be discovered, install additional fasteners as
needed and space them appropriately.
On all nailable roof decks, install a base sheet as the first layer below
the roof membrane. This base sheet serves as a separating layer between
the nailable deck and the roof membrane. Lap each base sheet a minimum
of 2 inches over the preceding sheet. Endlaps should be a minimum of 4
inches. Fasten the base sheets according to the manufacturer’s recom-
mendations.

Applying Single-Ply Materials

As stated earlier, there are several attachment methods, depending on
the single-ply material. System configurations change from specifica-
tion to specification and are predicated not only on the manufacturer’s
procedure, but on site conditions. This can and does leave some ques-
tions about the proper method to use.
Nonetheless, fundamental procedures for the correct installation of
all single-ply membranes remain the same, regardless of the system or
specification. The strength and waterproofing characteristics of single-
ply membrane systems depend on the construction of the laps and
seams between membrane sheets and between the membrane and
flashing materials.
Lap dimensions typically are specified as an amount of overlap
between adjacent sheets. Because of the many construction variables
already mentioned, some variance can occur. An overlap exceeding
the specification is not considered detrimental. The material sup-
plier’s minimum lap values must be maintained, however, so as not to
affect the strength and waterproof integrity of the membrane. Fabricate
membrane laps so that they are watertight. Repair voids and fish-
mouths within the lap.
Products are frequently supplied with laying lines. Use these lines
to position the subsequent course of material for compliance with
nominal lap requirements. Because of the variation in substrates,
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SINGLE-PLY ROOFING
157
products, and systems, refer to the material supplier’s specifications
for minimum requirements.
If the product does not have laying lines, use the material supplier’s
stated lap dimension as the minimum lap requirement. If examination
reveals insufficient lap width, install a strip no narrower than twice
the required lap over the deficient lap. Use the appropriate attachment
method. Check all laps of heat-welded systems for adequate bonding.
Seal any unbonded area.
Several factors determine the point at which work begins. For
water runoff, begin work at a high point on the roof and move toward
the low point. This prevents any drainage water from overnight rains
from working its way under the new roof. Always shingle membrane
laps with the flow of water or parallel to the flow of water.
Consider the deck type. Metal decks have corrugations that fall in
6-inch modular spacings. As with rigid insulation, fasten the mem-
brane to the top of the flutes to meet Factory Mutual Engineering
(FME) specifications. Because the exposed width of most full rolls of
exposed membrane is 671⁄2 inches, the edge of the sheet eventually
falls between the flutes when the membrane is run parallel to the
flutes. When this happens, trim the excess back to the nearest flute
top (Fig. 6-5A).
When the membrane is run perpendicular to the metal deck corru-
gations, the amount of trimming and membrane waste is less than it
would be if the membrane ran parallel to the corrugations (Fig. 6-5B).

Applying Thermoset Materials

Thermoset single-ply material can be applied loose-laid and ballasted,
partially adhered, or fully adhered. Always roll out the sheet and
allow it to relax. Inspect the sheet for defects as it is being rolled out.
To seal the laps, fold the sheet back onto itself and clean the under-
side of the top sheet and the upperside of the bottom sheet with the
recommended solvent to remove dirt and talc from the lap area. Apply
adhesive evenly to both surfaces and allow it to set according to the
manufacturer’s application instructions. Then roll the top sheet over
the bottom sheet in a manner that minimizes voids and wrinkles.
Apply pressure to the lap to ensure contact.
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158 CHAPTER SIX

Top
Top
108' view
view

Direction
W
of
a
Direction of membrane
s
6' membrane run Up to run
t
max. 108'
e

3" 3"

Side
Side view
view
A B
F I G U R E 6 - 5 (A) Membrane running parallel to metal decking might require trimming
along entire length of roll. (B) Membrane running perpendicular to the metal deck corru-
gations. The maximum trim is across the width of the roll.

LOOSE-LAID AND BALLASTED METHOD

With this method, the membrane is placed on a substrate without
bonding and held in place by ballast. NRCA recommends that consid-
eration be given to mechanically fastening or spot adhering the first
layer of insulation to the roof deck under loosely laid roof systems.
Only enough mechanical fasteners or adhesive need be used to hold
the insulation boards in place during installation of the roofing mem-
brane and to prevent stacking or displacement.
Attach the second layer of insulation, if used, to the first layer with a
compatible adhesive. As an alternative procedure for nailable roof decks,
both layers can be mechanically fastened to the deck at the same time.
Adhesive application quantities, mechanical fastener spacing, lap
dimensions, and other minimum installation requirements vary from
manufacturer to manufacturer. Over cellular glass insulation and any
other insulation substrate where rough surfaces, protrusions, or sharp
edges might affect the service of the membrane, install a separation
sheet between the insulation and the roof membrane. Fasten the sepa-
ration sheet only often enough to hold the sheets in place until the roof
membrane is applied.
Roll out and align the sheet so that it overlaps the previous sheet by
the required lap width. Seal all membrane laps together. Fabricate laps
to shed water whenever possible.
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SINGLE-PLY ROOFING
159
First layer
preformed
roof
insulation
board
EPDM sheet
Separation
layer
(if required)

Adhered seams
Second layer
preformed
roof
insulation
board
Ballast

F I G U R E 6 - 6 Loose-laid membrane system.

Ballast the loose-laid membrane with rounded stone, such as

washed river gravel (Fig. 6-6). The amount of needed ballast varies
with the location and height of the building. Substitute concrete
pavers for rounded stone ballast if a protective underlayment is
installed to protect the roof membrane from the abrasive surface of the
paver.

PARTIALLY ATTACHED SYSTEMS

There are three generic ways to partially attach a thermoset (EPDM)
membrane (Fig. 6-7). For the first method, roll out the sheet and align
it so that it overlaps the previous sheet by the required lap width.
Install mechanical fasteners with large washers or install bars with
mechanical fasteners through the membrane and into the deck. Cover
these fasteners or bars with membrane pieces that are bonded to the
membrane in a manner similar to the methods used for sealing laps.
Then seal all membrane laps together.
For the second method, roll out the sheet and install mechanical fas-
teners with large washers or bars with mechanical fasteners through the
membrane within the area of the lap and into the deck. Seal all mem-
brane laps together so that the fasteners are covered.
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160 CHAPTER SIX

First layer
preformed
roof insulation
board
Individual or bar-type
mechanical fastener
covered with membrane piece
Separation
layer
(if required)
EPDM sheet

Adhered seams
Second layer
preformed roof
Individual or bar-type insulation board
mechanical fastener
installed under lap

Proprietary nonpenetrating
fastening system

F I G U R E 6 - 7 Partially attached roof system.

For the third method, mechanically fasten a proprietary fastening

system in a predetermined pattern over the separation layer if used.
Install the roof membrane over the fasteners. Roll out and align the
sheet so that it overlaps the previous sheet by the required lap width.
Sandwich the membrane between the parts of the fastening system by
installing the second part of the mechanical fastener. Seal all mem-
brane laps together.

FULLY ATTACHED SYSTEMS

For sheet systems, total bonding is usually achieved by applying an
adhesive. The substrate for adhesive-bonded systems must be smooth,
clean, dry, and free from dust, dirt, grease, oil, wax, and loose particles.
Prime the substrate before applying the adhesive to achieve a greater
bond.
Contact adhesives usually are used in total bonding. They are
applied to the top surface of the substrate and the bottom of the sheet.
Some sheets are self-adhering, however, so that the bottom of the sheet
adheres to the substrate without an adhesive.
To apply a fully attached or total-bonded application, roll out the
sheet and align it so that it overlaps the previous sheet by the required
lap width. Fold the sheet back onto itself and coat the bottom side of
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SINGLE-PLY ROOFING
161
First layer
preformed roof
insulation board
Contact
adhesive
EPDM sheet

Second layer
preformed roof
insulation board

Adhered seams

F I G U R E 6 - 8 The mechanics of a fully adhered

roof system.

the membrane and the top side of the deck with adhesive. Avoid get-
ting adhesive on the lap joint area.
After the adhesive has set according to the adhesive manufacturer’s
application instructions, roll the membrane into the adhesive in a
manner that minimizes the occurrence of voids and wrinkles. Repeat
this for the other half of the sheet. Take care to adhere the very middle
of the sheet (Fig. 6-8). Then seal all membrane laps together. Fabricate
caps to shed water wherever possible.

Seaming Single-Ply Materials

A single-ply system is only as strong as its seams. There is more than
a little truth to this cliche, especially with elastomerics. Unlike hot
BUR, elastomeric and plastomeric sheets are preformed in the factory.
Most of the problems with these systems can be traced back to field
workmanship, of which lap seaming is a critical part. Most contractors
feel that poor workmanship is the most common reason for single-ply
roof failure. Industry experts are inclined to agree.
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162 CHAPTER SIX

Most rubber-based, single-ply membranes require adhesive for lap

seaming. A new generation of adhesives and sealants that speed appli-
cation and improve the performance of rubber-based systems is pro-
viding simplified design, ease of inspection, proven performance, and
low maintenance.

Bonding Adhesives
All-purpose bonding adhesives, geared toward roofing applications,
adhere EPDM, neoprene, and butyl roof membranes to wood, concrete,
metal, and certain insulation surfaces. These are contact-type adhesives.
Their use involves the application of a uniform coat to the back of
the rubber membrane, as well as to the surface to which it is to be
bonded. These successful products have earned wind-test ratings
from FM and are accepted by most code authorities. Manufacturers
advise that the mating surfaces be dry, clean, and free from oil,
grease, and other contaminants. The best working temperatures are
40°F or above.
Many EPDM suppliers currently use one-part butyl adhesives to seal
their 45- and 60-mil membranes. These adhesives normally give consis-
tent peel strengths in the range of 3 to 41⁄2 pounds per inch. The applica-
tion of one-part butyls is somewhat less forgiving than that of other
adhesive systems, however. The open time or window, defined as the
time from when the seam can first be closed to when it no longer grabs,
is shorter and varies with weather conditions. Keep in mind that one-
part butyl requires a heavier adhesive coating. It can skin over and give a
false indication that it is dry. In addition, it has been found that improp-
erly stirring the adhesive results in less-than-adequate peel strengths.
Butyl cement begins to cure when exposed to heat and moisture.
Once a can of adhesive is opened, do not reseal it or use it again
because a substantial thickening of the cement occurs in about 48
hours. On the other hand, if butyl goes bad, the applicator knows it
because the material does not stick. The pass/fail criteria for other
adhesives are not as obvious.

Splicing Adhesives
There are lap splicing adhesives for EPDM, neoprene, and butyl mem-
brane roofing. These adhesives provide long-lasting, weather-
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SINGLE-PLY ROOFING
163
resistant bonding between the single-ply membranes used in various
systems. Technology in the last five years has further enhanced the
long-term performance of these adhesives. The size of the splice deter-
mines the application. In most cases, for flashing and expansion joint
applications, the minimum splice width is 3 inches.
These also are contact adhesives that must be applied to both of the
surfaces being bonded. The splice area must be dry and completely
free of dust, talc, and other contaminants. The best working tempera-
tures are between 40° and 120°F.

Sealants
Adhesive-seamed, cured, and uncured elastomer membranes all
require the use of a lap sealant at the seam edge. Most adhesives are
vulnerable to moisture until fully cured. Some materials take as long
as a week to become fully moisture resistant. In addition to sealing
out moisture and other contaminants, the sealants absorb thermal
expansion and resist fatigue, vibration, and biological attack. They
are ideal for sealing roofing protrusions, cracks, duct work, and exte-
rior seams.
In order to allow the solvents to escape from inside the seam, do
not apply the lap sealant for at least 2 hours. If rain is imminent or
there is a need to leave the jobsite, apply the lap sealant earlier rather
than later. Repairing minor blistering in the caulked edge is always
easier than dealing with ruined seams.
It is also easy to wander off the membrane edge when you install
the lap sealant. Because of this, it is important to tool the sealant. Ide-
ally, one worker should install the material, while a second worker fol-
lows behind and tools the edge. If one waits too long to tool, the
material can harden and start building up on the tool. Sometimes a
primer is applied to the sheet before the adhesive to enhance seam per-
formance.
Unlike splice or primer washes, the solvent is applied at full
strength. The combination of primer and neoprene adhesive usually
offers performance similar to that of one-part butyl.
To apply the adhesive system, first use a splice cleaner on the seam.
After the area dries, roll the primary butyl adhesive over the entire
width of the splice. Next, apply a bead of inseam sealant tube on top of
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164 CHAPTER SIX

the butyl and roll the seam closed. Finally, secure the splice with a lap
sealant. The inseam sealant is also designed to serve as a redundant
adhesive. If the installer misses a small section of the seam with the
butyl, the inseam sealant should still adhere to the EPDM and seal the
seam. Because the sealant has a greater mass than the butyl adhesive,
it is capable of filling any voids or gaps in the seam created by an
uneven substrate.
Be aware that the inseam sealant does not have the green strength
to hold the seam together during setup time. Therefore, the butyl adhe-
sive must be installed in conjunction with the sealant to avoid fish-
mouths at the edge of the seam.

Tape
Butyl-based tape offers the extra mass of adhesive needed when three
layers of membrane come together, called a T-joint. According to
many roofers, the tape is somewhat more sensitive to dust, dirt, and
contaminants than the liquid adhesive. Applying the liquid adhesive
with a bristle brush can lift contaminants into the adhesive mass. On
the other hand, tapes have speed and labor-saving advantages, if the
applicator is skilled.
While many tapes used in the past were made of uncured material,
today’s tape adhesives are cured. Uncured tapes move independently
of the roof during expansion and contraction. Cured tape is able to
move with the sheet.

Heat Welding
Until recently, one of the easiest ways to tell if an applied single-ply
membrane was thermoset or thermoplastic was to look at the seams.
Thermoset seams were installed with adhesive tape or sealer, while
thermoplastic seams were usually heat-welded.
Several manufacturers are now producing a hot-air weldable EPDM
membrane, however, which eliminates the use of adhesives or tapes.
One product consists of a patented blend of polypropylene and vul-
canized rubber. The polypropylene gives the membrane heat-welded
characteristics and greater oil resistance, while EPDM and carbon
black protect the polypropylene from UV degradation. During manu-
facture, a codispersion between the EPDM and polypropylene takes
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SINGLE-PLY ROOFING
165
place,with the molecular crosslinking of the polypropylene already in
the EPDM formulation.
Another heat-weldable EPDM is made of polypropylene and a ther-
moplastic rubber. A coextrusion process causes the crosslinking of the
two materials, with the top layer containing more vulcanized rubber
and the bottom layer more polypropylene.
The 45-mil membrane is mechanically fastened in seam using 2-
inch-diameter washers set 18 inches on center. A UL Class 90 wind-
uplift rating and Class B fire rating (smooth surfaced) have already been
achieved. Tear strength is a consideration in a nonreinforced, mechani-
cally attached sheet. The crosslinking process gives the membrane a
360-pounds-per-square-inch tear strength across the sheet, which is
where wind uplift forces are greatest, according to the manufacturer.
CSPE, as mentioned earlier in the chapter, is heat-welded.

Applying Thermoplastic Materials

PVC, CPE, and PVC blends can be installed by loose-laid, partially
attached, or fully adhered methods.

Using the Loose-Laid Method

On all nailable roof decks, install a separator sheet as the first layer
below the roof membrane to serve as a separating layer between the
nailable deck and the roof membrane (Fig. 6-9A and B). Lap each sep-
arator sheet a minimum of 2 inches over the preceding sheet. Endlaps
should lap a minimum of 4 inches. Fasten the separator sheets only as
necessary to hold the sheets in place until the roof membrane is
applied.
Roll out the sheet over the separator sheet and inspect the mem-
brane for defects. Align the sheet so that it overlaps the previous sheet
by the required lap width. Seal all membrane laps together using either
heat welding or chemical fusion. Fabricate laps to shed water wherever
possible. Apply pressure to the lap to improve the bond.
Carefully inspect lap edges. Repair unsealed areas, voids, and
fishmouths. Generally, manufacturers require that exposed mem-
brane edges be finished with a sealant. Fasten all membrane perime-
ters, terminations, and penetrations as required by the manufacturer.
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166 CHAPTER SIX

Ballast the loosely laid mem-

Nailable deck brane with rounded stone, such
PVC sheet as washed river gravel. The
amount of ballast needed varies
with the location and height of
the building. Concrete pavers
can be substituted for rounded
Heat-welded or stone ballast, provided that a
chemically fused laps
Separator protective underlayment is
sheet installed to protect the roof
Ballast membrane from the abrasive sur-
face of the paver.
A
First layer Using the Partially
preformed
roof insulation Attached Method
board
PVC sheet
Separator
There are three generic methods
sheet
(if required)
for partially attaching thermoplas-
tic membranes (Fig. 6-10). For the
Heat-welded or Second layer first method, mechanically fasten
preformed roof
chemically fused laps
insulation board PVC-coated metal discs in a prede-
termined pattern over the separa-
tor sheet. Roll out the membrane
Ballast
and inspect it for defects. Heat
B weld or chemically weld the
F I G U R E 6 - 9 (A) Loosely laid PVC sheet membrane to the PVC-coated
over a nailable deck. (B) Loosely laid PVC metal discs as the membrane is
over an insulated deck. rolled out onto the deck. Align the
sheet so that it overlaps the previ-
ous sheet by the required lap width. Then seal all membrane laps using
heat welding or chemical fusion. Fabricate laps to shed water wherever
possible. Apply pressure to the lap to improve the bond.
The second method calls for the installation of mechanical fasten-
ers with large washers through the membrane and into the deck. Cover
these fasteners with membrane patches and heat weld or chemically
fuse the patches to the membrane. Seal the membrane laps using heat
welding or chemical fusion. Fabricate the laps to shed water and apply
pressure to the lap to improve the bond.
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SINGLE-PLY ROOFING
167
The third method follows the Mechanical fastener
covered with membrane
Nailable deck
same initial steps. Roll out and piece

inspect the membrane and seal

PVC sheet Sheet
the laps using heat welding or welded to
mechanically
chemical fusion. Fabricate the fastened
PVC disk
laps to shed water, and apply
Heat-welded or
pressure to the lap to improve the chemically fused laps
bond. Then place continuous
metal bars in a pre-engineered Separator
Bar-type fastener sheet
pattern on top of the membrane covered with membrane
piece
and mechanically fasten them to
the nailable roof deck. Cover the
bars with membrane patches that F I G U R E 6 - 1 0 Partially attached PVC roof
are heat welded or chemically system.

fused to the membrane.

Using the Fully Adhering

Method Wood plank or
plywood deck
There are two generic methods PVC sheet
Water-or
for fully adhering thermoplastic solvent-based
adhesive
membranes (Fig. 6-11). For sol-
vent-based adhesives, roll out the
sheet and inspect it for defects.
Align the sheet so that it overlaps Heat-welded or
chemically fused laps
the previous sheet by the
required lap width. Fold the
sheet back onto itself and coat the
bottom side of the membrane and
F I G U R E 6 - 1 1 A fully adhered PVC roof
the top side of the deck with system.
adhesive. Avoid getting adhesive
on the lap joint area.
After the adhesive has set according to the manufacturer’s appli-
cation instructions, roll the membrane into the adhesive in a manner
that minimizes the occurrence of voids and wrinkles. Repeat this for
the other half of the sheet. Carefully adhere the middle of the sheet.
For water-based adhesives, follow the steps for solvent-based adhe-
sives, but avoid getting the adhesive on the lap joint area when you
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168 CHAPTER SIX

coat the deck. After the adhesive sets according to the manufacturer’s
application instructions, roll the membrane into the adhesive in a
manner that minimizes the occurrence of voids and wrinkles.

Seaming Thermoplastics
PVC, CPE, and the PVC blends are inherently heat weldable with typical
lap seam strengths of more than 20 pounds per inch. While hot-air and
solvent welding procedures are quicker than adhesive seaming, a con-
siderable amount of applicator skill is still required. For example, CPE
exhibits a higher melting temperature than most PVCs and a narrower
welding window. It is especially important to conduct test welds when
ambient roof conditions change substantially.
There are two basic types of welders available: automatic and hand.
The automatic welder rides on the top sheet, which is being welded to the
bottom sheet. For this reason, it is possible to start welding in one of two
roof corners: the upper right-hand corner or the lower left-hand corner
(Fig. 6-12). To determine these two corners, face the same direction as the
run of the membrane. The roof corners to your upper right and lower left
are the possible starting points.
Automatic
welding machine Use the hand welder to weld
Upper right seams when automatic welding is
not possible, such as near a para-
Welder
start pet wall or curb detail. Hand
position
and welding is also used for many
direction
of travel flashing details, applying mem-
brane patches, and repairing poor
or unfinished machine-welded
Second First seams (Fig. 6-13).
full full
sheet sheet When the gun heats the mem-
brane to a semimolten state, use a
hand roller to bond the lap seam.
A number of interchangeable
nozzle tips are designed to match
Lower left
any hand-welding situation. For
F I G U R E 6 - 1 2 Welding can begin at one heavily reinforced PVC blends,
of two points on the roof, the upper right applying pressure at the right
or the lower left. temperature is crucial to a good
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SINGLE-PLY ROOFING
169

F I G U R E 6 - 1 3 A hand welder in use.

lap seal. Because there are several models and designs, always follow
the adjustment procedures (Fig. 6-14) outlined in the service manual
(see App. A for vendors).

Checking Welded Seams

Working conditions vary from job to job, from day to day, and even
from hour to hour. Varying conditions require different heat and speed
settings on the welding machine. Because conditions vary, it is
extremely important that you inspect all welded seams with care.
Make adjustments to welder speed, temperature, and setup as needed.
Wait several minutes before testing seam strength, since even good
welds can be separated while they are still hot. A good weld is one
where the top sheet does not separate from the bottom sheet without
damaging the membrane.
Proper seam width is approximately 11⁄2 inches. The welded seam
should be smooth and continuously bonded without voids or air pock-
ets. The lap edge should be bonded completely together. Check for
gaps in this seam by running a cotter-pin puller along the seam.
The automatic welder usually misses the first few inches of a
seam, so pull back the lap after it has cooled and mark off the area that
requires hand welding. If there are voids in the weld seam, or if the
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170 CHAPTER SIX

F I G U R E 6 - 1 4 Making an adjustment on a hand

welder.

finished seam is weak, it probably means that the hot-air nozzle did
not have enough time to heat the membrane to the necessary molten
state. To correct this problem, slightly lower the machine’s welding
speed and make another test run.
Other problems, such as dirt on the membrane, moisture on the
membrane, or variances in the power supply, also can produce
voids and poor bonding. Inspect the welded seam and the area
around the weld. A light browning or burning of the membrane
indicates that the nozzle is overheating the weld area. To correct
this, increase the welding speed slightly and test again.
If the membrane still burns at the highest speed setting, lower the
nozzle temperature by adjusting the heat control dial. Brown streaks at
the edge of the overlap usually are caused by the outer edge of the noz-
zle dragging heated dirt and membrane particles across the membrane.
To prevent this, clean the nozzle with a wire brush.
Pinch wrinkles can be pulled into the membrane sheets when the
automatic welder is not set up properly. If pinch wrinkles occur,
review the setup and operating procedures given earlier in this section
and those provided with the welder. Repair pinch wrinkles with mem-
brane patches.
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171
Applying Modified Bitumen Materials
MBR can be applied using torch-applied, hot-mopped asphalt or a self-
adhered method.

Torch-Applied or Heat-Weld Method

To apply the membrane, roll out the sheet and inspect it for defects.
Align the sheet so that it overlays the previous sheet by the required
lap width and then reroll it. Heat the underside of the roll to soften
the bitumen coating. Take care not to overheat the top surface of the
sheet.
Most torch-applied membranes come with a factory-installed burn-
off film. This film is usually polyethylene, though it can be polypropy-
lene. Burn-off films are applied as a release agent and as a compatible
material that blends with the MBR coating when heated. This creates
an excellent cohesive bond at the lap or seam. Films also facilitate
bonding to other surfaces. Some torch-down products incorporate talc
or sand as a release instead of burn-off films.
To obtain flow of the MBR coatings, apply heat to the burn-off film
surface in sufficient amounts to soften and melt the coating. When the
roll is unwound you should see a flow ahead of the roll and at the side-
lap that minimizes voids and wrinkles. At the sidelap and all seams,
flow should be from a minimum of 1⁄4 inch to a maximum of 1⁄2 inch. It
should be continuous and uninterrupted. No flow at all indicates that
insufficient heat was applied. A flow more than 1⁄2 inch indicates that
too much heat was applied.
Take care to ensure proper lap alignment. Membrane laps are
sealed together as the sheet is adhered to the deck. Fabricate laps to
shed water wherever possible. Check all seams for proper bonding.
Check any lap or seam that has no flow for integrity. Some manufac-
turers require that all seams be buttered or troweled. In most cases,
however, this is not necessary.
Any installation areas that have an observable flow in excess of
1
⁄2 inch are not likely to have bonding surfaces. This yields the max-
imum effect because of excess coating flow. In some cases, the coat-
ing can be almost completely forced away from the bonding
surfaces, which reduces maximum bonding potential.
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172 CHAPTER SIX

Excess heat also can affect polyester-reinforced membranes. These

membranes are susceptible to stretch and thermal breakdown if too
much heat is applied. Polyester burns and melts, which dramatically
reduces performance characteristics. Fiberglass-reinforced mem-
branes do not stretch under heat. They can, however, experience ther-
mal breakdown of binders, which can result in a loss of performance
characteristics.

Hot-Mopped Method
Roll out and inspect the sheet. Then align the sheet so that it overlaps
the previous sheet by the required lap width. Reroll the membrane.
Apply a mopping of hot asphalt immediately in front of the roll. Fol-
low the guidelines for heating asphalt as predicated by the equiviscous
temperature (EVT) printed on the carton or wrapper, or review Table
5-1. Never heat the asphalt to its flash-point temperature.
Align the membrane plies carefully. Stagger or offset endlaps a
minimum of 3 feet. Apply the first membrane course at the lowest
point of the deck. This prevents water from flowing against the lap
seams. Mop consistently at about 25 pounds per square. The mopping
action should be continuous and uninterrupted when fully adhered
systems are installed. Do not feather or taper moppings.
When applying the hot-asphalt-applied MBR membrane, advance
the roll into hot asphalt that has been applied no more than 4 feet in
front of the roll. Moppings more than 4 feet from the advancing roll
can cool and cause false bonding. Check all laps and seams for proper
bonding. Fabricate the laps to shed water whenever possible.
Flow from the mopping asphalt at laps and seams should be from the
torch-applied membrane. Use a thermometer to check asphalt tempera-
tures at each point before application.
For added protection and aesthetics, mineral granules can be sprin-
kled on the asphalt flow at all laps and seams while the asphalt is still
hot. Other materials can also be used to surface MBR membranes. In
addition to their primary function to protect the membrane from the
elements, these surfacings often serve to increase the fire and impact
resistance of the roofing system.
Liquid-applied surfacing materials vary in physical properties and
in formulation. Surfacing materials and aggregate are applied by vari-
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SINGLE-PLY ROOFING
173
ous techniques, such as hand spreading and mechanical application.
They also are applied on a variety of roofs in many climatic conditions.
These factors and others preclude a high degree of uniformity in apply-
ing liquid-applied surfacing materials and aggregate over a roof area.
Hot-asphalt-applied membranes come with a sand release that is
used as an antiblocking agent and as a surface that facilitates adhesion
to the asphalt. Hot-asphalt-applied MBR membranes are always SBS-
modified bitumens with a sanded bonding surface.

Self-Adhered Method
Cold adhesives are used with some MBR membranes to bond the sheet
to the substrate. Use the adhesive specified by the material supplier.
During the application of a fully adhered system, you should observe
a continuous, firmly bonding film of adhesive. The adhesive should
flow out from the membrane to form a seal. If aesthetic appearance is
a factor or is dictated by specification, matching granules can be used
to cover the flow-out area.
When using the fully self-adhered application, prime the surface of
the roof deck with asphalt primer and allow it to dry. Primers are not
required if a base sheet is used. Roll out the sheet, inspect it for
defects, and align it so that the membrane overlaps the previous sheet
by the required lap width. Then reroll it.
Remove the release paper from the underside of the membrane and
roll the membrane over the primed surface in a manner that minimizes
voids and wrinkles. Take care to ensure proper lap alignment. Mem-
brane laps are sealed together as the sheet is adhered to the deck. Fab-
ricate laps to shed water whenever possible. Apply pressure to both
the membrane and lap areas to ensure contact.
In a partially adhered membrane application, MBR compounds,
asphalt, and adhesives are used to secure the roof assembly to the
structure. These materials are installed in a configuration prescribed
by the material supplier, such as spot or strip bonding. They often are
specified by amount and spacing distances. Practical considerations
often prevent the application of the exact amount and spacing, such as
12 inches in diameter and 24 inches on center of the bonding agent.
Reasonable variances are expected.
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174 CHAPTER SIX

The application should result in a firmly bonded membrane. The

spacing of the bonding agent should be specified by the material sup-
plier. The design team and owner should understand that the spacings
are average values and that the distance between any two adhesive
locations can vary. Correct deficiencies by installing an additional
bonding agent as needed. Space appropriately. Determine the scope of
the discrepancy and take appropriate remedial action.

Flashing at Terminations
Single-ply membrane terminations at roof edges, parapets, and flash-
ing are treated in a variety of ways depending on the material used.

Cured Elastomeric Membrane Flashing

Cured elastomeric membrane that is identical to the roof membrane
material can be used as flashing material. Cut the membrane to size and
coat the bottom side of the flashing membrane and the area to be
flashed with adhesive. After the adhesive has set according to the man-
ufacturer’s application instructions, roll the membrane into the adhe-
sive in a manner that minimizes the occurrence of voids and wrinkles.
Exercise care that the flashing does not bridge where there is a
change of direction, i.e., where the parapet wall intersects the roof
deck. Seal joints where the cured elastomeric membrane flashing
material meets with roof membrane in a manner similar to that used
for membrane laps. Apply pressure to the laps to ensure contact.

Uncured Elastomeric Membrane Flashing

Uncured elastomeric membrane can be used in lieu of cured elas-
tomeric material. It is especially suited for penetrations, corners, and
other flashings where the membrane must be formed or must change
direction. The uncured membrane is used in a manner similar to cured
membrane material. Upon curing, however, it permanently shapes to
conform to the substrate being flashed.

PVC-Coated or PVC-Clad Metal Flashing

PVC-coated or PVC-clad metal can be used as flashing material. The
flat metal stock is cut and fabricated to the proper shape to meet field
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SINGLE-PLY ROOFING
175
requirements. The sheet metal pieces should not exceed 10 feet in
length. Fasten the metal in place with fasteners typically spaced 4 to 6
inches on center. Round the corners and the edges of the sheet metal
flashing to protect the membrane from punctures or chafing. Cover the
gap with tape.
Splice the two pieces of metal together with a minimum 5-inch-
wide piece of PVC membrane. Center the piece on the gap so that it
extends from the top of the metal flashing and out onto the field of the
roof. Either heat weld or chemically fuse the PVC membrane to the
PVC-clad or PVC-coated metal flashing.

Reinforced PVC Membrane Flashing

Reinforced PVC membrane flashing can be used in lieu of PVC-coated or
PVC-clad metal flashing provided the membrane is first mechanically
fastened to the nailable roof deck at the flashing. Fasten the reinforced
PVC membrane flashing at its upper edge, and shape it to conform to the
parapet wall, curb, or edging. Then extend the reinforced flashing onto
the field of the roof a minimum of 4 inches. Heat-weld or chemically
fuse it to the roof membrane. Endlaps are to be a minimum of 4 inches.
Heat-weld or chemically fuse them to the adjoining piece of flashing.
Various PVC flashing details are shown in Fig. 6-15.

MBR Flashing Systems

MBR flashing materials are applied using a variety of methods, includ-
ing heat welding, hot asphalt, and adhesive applications. The degree of
heat required for appropriate heat welding, the variables affecting the
application rates and temperatures of any asphalt used, and the amount
of adhesive used are subject to many variables, including weather con-
ditions, job conditions, material type, and application method.
In addition, the material supplier’s requirements must be consid-
ered. Membrane termination follows the same basic procedure at roof
edges, parapets, and other flashing applications as the BUR materials
described earlier. It can be handled in one of three ways.
Torch-applied MBR membranes can be used as flashing material for
masonry, concrete walls, curbs, or other noncombustible substrates. Cut
the membrane material to size and prime the wall or curb and the area
of the roof membrane to be flashed. Place the MBR flashing membrane
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176 CHAPTER SIX

CPE coated metal drip edge

with hemmed edge
Continuous hook strip 22-ga. galv.
secure with annular ring nails 6"
on center
CPE seam sealer
Heat-welded lap

Annular ring shank nails 4"

on center

5" max.

Wolmanized wood
nailer secured to Roof deck
deck; min. 5" wide Insulation
Cool-top roof membrane
A

Always reuse existing

through-wall counterflashing
Fasten 8" on center
CPE coated metal
Varies Provide a cant bend into metal
Seam sealer
with Heat-welded lap
existing Cool-top roof membrane 5" flange with
conditions hemmed edge fastened 4" on center
using annular ring nails

Roof deck
Existing insulation
Existing roof
New insulation

B
F I G U R E 6 - 1 5 (A) CPE-coated metal drip edge.
(B) Installing coated metal flashing under existing
wall counter. (C) Heated vent-pipe flashing.

bottom-side up onto a plywood or other suitable platform. Heat the

underside of the membrane with a torch to soften the coating bitumen.
Set the heated membrane material to the wall or curb in a manner
that minimizes the occurrence of voids and wrinkles. Take care that
the flashing does not bridge where there is a change of direction, such
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SINGLE-PLY ROOFING
177
Urethane or polysulfide caulking by others

Stainless steel hose clamp

One-piece CRSI CPI boot

Vent pipe Min 4 CBSI coated

plates and screws
equally spaced max. 12"
on center around the pipe

Cool-top 2" heat-welded lap

roof membrane

CPE seam sealer

Roof deck

Insulation
C
F I G U R E 6 - 1 5 (Continued)

as where the parapet wall intersects the roof deck. Seal the joints
where the MBR flashing material meets with the roof membrane in a
manner similar to that used for membrane laps. Apply pressure to the
laps to ensure contact.
Hot-mopped MBR membranes can also be used as flashing mater-
ial. Follow the directions for torch-applied membranes. Instead of
torching, apply hot asphalt to the area to be flashed and then to the
underside of the membrane. Seal the joints where the MBR flashing
material meets with the roof membrane in a manner similar to that
used for membrane laps. Apply pressure to the laps to ensure contact.
The third method is to use self-adhered MBR membranes as flash-
ing material. Cut the membrane material to size and prime the wall or
curb and the area of the roof membrane to be flashed. Remove the
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178 CHAPTER SIX

release paper and set the membrane to the wall or curb in a manner
that minimizes the occurrence of voids and wrinkles. Take care that
the flashing does not bridge where there is a change of direction. Seal
the joints where the MBR flashing material meets with the roof mem-
brane in a manner similar to that used for membrane laps. Apply pres-
sure to the laps to ensure contact.
Locate the flashing terminations a minimum of 8 inches above the
level on the roof. Counterflashing should follow the material sup-
plier’s specifications. Some material suppliers have a maximum
height limitation for flashings. Refer to the material supplier’s recom-
mendations.
A cant strip can be installed to modify the angle between the roof
deck and the vertical surface. For heat-welded applications, make cant
strips from a flame-resistant material and cover them with a base felt.
Consult the manufacturer’s instructions for recommendations regard-
ing the use of cant strips.
Install the membrane before the flashing is applied and above the
plane of the roof, above the cant, and up the vertical surface as speci-
fied by the material supplier. Do not run the roof membrane up the ver-
tical surface to act solely as a base flashing. Remove and reinstall areas
of loose, inadequately or improperly bonded flashings using the same
materials used in the original application. Cut out, rebond, and rein-
stall laps that are inadequately bonded.
Carefully inspect flashing seams; repair unsealed areas, voids, and
fishmouths. Smoothly finish exposed edges or torch-applied MBR
membrane with a hot, rounded trowel.

Surfacing Single-Ply Roofs

Some MBR membranes have factory-applied surfacings that provide
weather resistance or improve the appearance of the roof membrane.
Some membranes require that the surfacings or coatings that provide
these properties be applied in the field. The following is a description
of the more common surfacing options for MBR systems.

Ballast. Loosely laid MBR systems require the use of ballast to build
resistance to wind-uplift forces. The ballast is usually rounded
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SINGLE-PLY ROOFING
179
stone, such as washed river gravel. The amount of ballast needed
varies with the location and height of the building. Concrete pavers
can be substituted for rounded stone ballast, provided that the roof
membrane is protected from the abrasive surface of the paver.
Aggregate. For fire resistance, the application of a flood coat and
aggregate surfacing can be required. The aggregate should be essen-
tially opaque and a nominal 3⁄8 inch in diameter. Embed the aggre-
gate in a flood coat of hot asphalt.
Mineral granules. For fire resistance, some membranes require the
field application of mineral granule surfacing. For each roof square,
embed approximately 50 pounds of No. 11 roofing granules in an
emulsion coating that has been applied to the membrane at the
approximate rate of 2 gallons per roof square (see manufacturer’s
instructions).
Emulsion coatings. For aesthetics, some membranes require the appli-
cation of an asphalt emulsion top coating. Application rates and
techniques vary from manufacturer to manufacturer.
Reflective coatings. Fibered and nonfibered aluminum/asphalt coat-
ings can be applied to most smooth-surfaced MBR membranes.
Application rates and techniques vary depending on the manufac-
turer.
Factory-applied/self-surfaced membranes. Some MBR membranes
might not require the field application of additional surfacing
materials. These include membranes with factory-applied mineral
granules or metal foils and some smooth-surfaced systems.