Designation: C 981 – 05

Standard Guide for

Design of Built-Up Bituminous Membrane Waterproofing
Systems for Building Decks1
This standard is issued under the fixed designation C 981; the number immediately following the designation indicates the year of
original adoption or, in the case of revision, the year of last revision. A number in parentheses indicates the year of last reapproval. A
superscript epsilon (e) indicates an editorial change since the last revision or reapproval.

1. Scope D 41 Specification for Asphalt Primer Used in Roofing,

1.1 This guide describes the design of fully adhered built-up Dampproofing, and Waterproofing
bituminous membrane waterproofing systems for plaza deck D 43 Specification for Coal Tar Primer Used in Roofing,
and promenade construction over occupied spaces of buildings Dampproofing, and Waterproofing
where covered by a separate wearing course. D 173 Specification for Bitumen-Saturated Cotton Fabrics
1.2 The values stated in SI units are to be regarded as the Used in Roofing and Waterproofing
standard. The values given in parentheses are for information D 226 Specification for Asphalt-Saturated Organic Felt
only. Used in Roofing and Waterproofing
1.3 The committee with jurisdiction over this standard is not D 227 Specification for Coal-Tar-Saturated Organic Felt
aware of any comparable standards published by other orga- Used in Roofing and Waterproofing
nizations. D 312 Specification for Asphalt Used in Roofing
1.4 This standard does not purport to address all of the D 449 Specification for Asphalt Used in Dampproofing and
safety concerns, if any, associated with its use. It is the Waterproofing
responsibility of the user of this standard to establish appro- D 450 Specification for Coal-Tar Pitch Used in Roofing,
priate safety and health practices and determine the applica- Dampproofing, and Waterproofing
bility of regulatory limitations prior to use. D 1079 Terminology Relating to Roofing and Waterproof-
ing
2. Referenced Documents D 1327 Specification for Bitumen-Saturated Woven Burlap
2.1 ASTM Standards: 2 Fabrics Used in Roofing and Waterproofing
C 33 Specification for Concrete Aggregates D 1668 Specification for Glass Fabrics (Woven and
C 578 Specification for Rigid, Cellular Polystyrene Thermal Treated) for Roofing and Waterproofing
Insulation D 2178 Specification for Asphalt Glass Felt Used in Roof-
C 717 Terminology of Building Seals and Sealants ing and Waterproofing
C 755 Practice for Selection of Water Vapor Retarders for D 2822 Specification for Asphalt Roof Cement, Asbestos-
Thermal Insulation Containing
C 1193 Guide for Use of Joint Sealants D 4022 Specification for Coal Tar Roof Cement, Asbestos
C 1299 Guide for Use in Selection of Liquid-Applied Seal- Containing
ants D 4586 Specfication for Asphalt Roof Cement, Asbestos-
C 1472 Guide for Calculating Movement and Other Effects Free
When Establishing Sealant Joint Width D 4601 Specification for Asphalt-Coated Glass Fiber Base
Sheet Used in Roofing
D 4990 Specification for Coal Tar Glass Felt Used in
Roofing and Waterproofing
1
This guide is under the jurisdiction of ASTM Committee D08 on Roofing and D 5295 Guide for Preparation of Concrete Surfaces for
Waterproofing and is the direct responsibility of Subcommittee D08.22 on Water-
proofing and Dampproofing Systems. Adhered (Bonded) Membrane Waterproofing Systems
Current edition approved July 1, 2005. Published August 2005. Originally D 5898 Guide for Details for Adhered Sheet Waterproofing
approved in 1983. Last previous edition approved in 2001 as C 981 – 01.
2
D 5957 Guide for Flood Testing Horizontal Waterproofing
For referenced ASTM standards, visit the ASTM website, www.astm.org, or
Installations
contact ASTM Customer Service at service@astm.org. For Annual Book of ASTM
Standards volume information, refer to the standard’s Document Summary page on D 6152 Specification for SEBS-Modified Mopping Asphalt
the ASTM website. Used in Roofing

Copyright © ASTM International, 100 Barr Harbor Drive, PO Box C700, West Conshohocken, PA 19428-2959, United States.

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 C 981 – 05
D 6162 Specification for Styrene Butadiene Styrene (SBS) temperature extremes of the inner and outer surfaces, precipi-
Modified Bituminous Sheet Materials Using a Combina- tation rates, solar exposure, prevailing wind direction, the
tion of Polyester and Glass Fiber Reinforcements pattern and reflectivity of adjacent structures, anticipated
D 6163 Specification for Styrene Butadiene Styrene (SBS) amount and intensity of vibration resulting from function or
Modified Bituminous Sheet Materials Using Glass Fiber adjacent occupancies, and design live loads both normal and
Reinforcements emergency.
D 6164 Specification for Styrene Butadiene Styrene (SBS) 6.2 It is essential that all components and contiguous
Modified Bituminous Sheet Materials Using Polyester elements be compatible and coordinated to form a totally
Reinforcements integrated waterproofing system.
D 6451 Guide for Application of Asphalt Based Protection 6.3 The plaza deck system is normally composed of several
Board subsystems: the structural building deck (membrane substrate),
D 6622 Guide for Application of Fully Adhered Hot- the waterproofing membrane, the drainage subsystem, the
Applied Reinforced Waterproofing Systems thermal insulation, protection or working slab, and the wearing
2.2 Other Documents: course (see Fig. 1). Fig. 1 as well as details, subsystems,
ACI 301 Specifications for Structural Concrete in Build- components, and illustrations that follow are intended to
ings3 illustrate a principle but are not necessarily the only solution
for a diversity of environments.
3. Terminology
3.1 Definitions—For definitions of terms used in the guide, 7. Substrate
refer to Terminologies C 717 and D 1079. 7.1 The building deck or substrate referred to in this guide
3.2 Definitions of Terms Specific to This Standard: is reinforced cast-in-place structural concrete.
3.2.1 prefabricated drainage composite—a preformed po- 7.1.1 High early strength and lightweight insulating con-
rous material, usually plastic, with a filter-type fabric over it. cretes do not provide suitable substrates. Additives made to the
concrete mix (such as calcium chloride) to promote curing,
4. Significance and Use reduce water requirements, or modify application temperature
4.1 This guide provides information and guidelines for the requirements should not be used unless the manufacturer of the
selection of components and the design of a built-up bitumi- waterproofing system specifically agrees.
nous membrane waterproofing system in building deck con- 7.1.2 Precast concrete slabs pose more technical problems
struction. Where the state of the art is such that criteria for than cast-in-place concrete, and the probability of lasting
particular conditions are not established or have numerous
variables that require consideration, applicable portions of
Design Considerations, Sections 5-16, serve as reference and
guidance for selection by the designer of the system.

5. Comparison to Other Standards

5.1 The Committee with jurisdiction over this standard is
not aware of any comparable standards published by other
organizations.
5.2 For application methods, refer to Guide D 6622. For
design of typical details not addressed in this guide, refer to
Guide D 5898.

6. General
6.1 The design of plaza deck waterproofing cannot be
satisfactorily determined without consideratoin of the several
subsystems, their material components, and interrelationships.
The proper selection from a variety of components that form a
built-up bituminous membrane waterproofing system must be
predicated upon specific project requirements and the interre-
lationship of components. The variety of the types of surfaces
exposed to weather, the difference of climatic conditions to
which the deck is exposed, and the interior environmental
requirements of the occupied space are major determinants in
the process of component selection. Essential to determination
of the deck design components is information relative to

FIG. 1 Basic Components of Built-up Bituminous Membrane Wa-

3
Available from ACI International, PO Box 9094, Farmington Hills, MI terproofing System with Separate Wearing Course (see Section
48333–9094. 6.3)

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 C 981 – 05
watertightness is greatly diminished and difficult to achieve unanimity in this regard, it is necessary to conform to the
because of the multitude of joints that have the capability of manufacturer’s requirements for the particular membrane be-
movement and must be treated accordingly. Moving joints are ing applied. Adequate drying of residual moisture from slabs
critical features of waterproofing systems and are more critical poured over a permanent metal deck will normally take longer
when sealed at the membrane level than at a higher level with than from slabs stripped of forming. Subsequent underside
the use of integral concrete curbs. Such curbs are impractical painting of stripped concrete slabs that might inhibit moisture
with precast concrete slabs and necessitate an even more vapor transmission and possibly cause loss of membrane
impractical drain in each slab. Other disadvantages of precast adhesion should be avoided.
concrete slabs are their inflexibility in achieving contoured 7.7 Joints—Joints in a structural concrete slab are herein
slope to drains and the difficulty of coordinating the placement referred to as reinforced joints, unreinforced joints, and expan-
of such drains. sion joints.
7.2 Slope for Drainage—Drainage at the membrane level is 7.7.1 Reinforced Joints—Reinforced joints consist of hair-
important. When the waterproofing membrane is placed di- line cracks, cold joints, construction joints, and isolation joints
rectly on the concrete slab, a monolithic concrete substrate held together with reinforcing steel bars or wire fabric. These
slope of a minimum 2 % (1⁄4 in./ ft.) should be maintained. The are considered static joints with little or no movement antici-
maximum slope is related to the type of membrane used. Slope pated because the slab reinforcement is continuous across the
is best achieved with a monolithic pour as compared with a joint.
separate concrete fill. The fill presents the potential of addi- 7.7.2 Nonreinforced Joints—Nonreinforced joints consist of
tional cracks and provides a cleavage plane between the fill and butt-type construction joints and isolation joints not held
structural slab. This cleavage plane complicates the detection together with reinforcing steel bars or wire fabric. These joints
of leakage in the event that water should penetrate the are generally considered by the designer of the structural
membrane at a crack in the fill and travel along the separation system as nonmoving or static joints. However, the joints
until reaching a crack in the structural slab. should be considered as capable of having some movement, the
7.3 Strength—The strength of concrete is a factor to be magnitude of which is difficult to predict.
considered with respect to the built-up bituminous membrane 7.7.3 Expansion and Seismic Joints—Expansion joints, as
insofar as it relates to finish, bond strength, and continuing differentiated from control joints, are designed to accommo-
integrity. The cast-in-place structural concrete should have a date movement in more than one direction, are an integral part
minimum density of 1762 kg/m3 (110 lb/ft3). of the building structural system, and must be carried through
7.4 Finish—The structural slab should have a finish of the entire structure. Expansion joints are incorporated in the
sufficiently rough texture to provide a mechanical bond for the structural frame (1) to reduce internal stresses caused by wide
membrane but not so rough to preclude achieving continuity of temperature ranges or differential movement, or both, between
the membrane across the surface. As a minimum, ACI 301 structural elements as might be the case in large adjoining
floated finish is required with ACI 301 troweled finish pre- heated and unheated spaces; (2) where there are different
ferred, deleting the final troweling. foundation settlement conditions between adjacent elements;
7.5 Curing—Curing the structural slab is necessary to or (3) where movements between high- and low-attached
provide a sound concrete surface and to obtain the quality of structures are anticipated. Seismic joints are a special case in
concrete required. Curing is accomplished chemically with which the joints are generally quite large and are designed to
moisture and should not be construed as drying. limit damage to the structural frame during earthquakes.
Expansion and seismic joints are best located at high points of
7.5.1 Moist Curing—Moist curing is achieved by keeping
contoured substrates to deflect water away from the joint. For
the surfaces continuously wet by covering with burlap satu-
expansion joints designed for thermal movement only, the
rated with water and kept wet by spraying or hosing. The
movement is expected to be only in the horizontal plane.
covering materials should be placed to provide complete
Seismic joints are designed to accommodate both vertical and
surface coverage with joints lapped a minimum of 75 mm (3
horizontal movement.
in.).
7.8 Flashing Substrate—The vertical surface that the mem-
7.5.2 Sheet Curing—Sheet curing is accomplished with a brane waterproofing intersects must be sound, with a smooth or
sheet vapor retarder that reduces the loss of water from the floated finish, dry, and free of cracks and loose materials as
concrete and moistens the surface of the concrete by conden- stated for the horizontal or deck substrate. The vertical surfaces
sation, thus preventing the surface from drying while curing. may be of concrete, stone, or masonry, and should be rein-
Laps of sheets covering the slab should be not less than 50 mm forced against shrinkage and cracks.
(2 in.) and should be sealed or weighted (see Practice C 755).
7.5.3 Chemical Curing—Liquid or chemical curing com- 8. Waterproofing Membrane
pounds applied to the surface of the structural slab should not 8.1 The major membrane components include primers,
be used unless approved by the manufacturer of the built-up bitumens, reinforcements and flashing materials.
bituminous membrane as the material may interfere with the 8.2 Primers—Primers (Specifications D 41 and D 43) are
bond of the membrane to the structural slab. used to prepare the substrate to obtain maximum adhesion of
7.6 Dryness—Membrane manufacturer’s requirements for the bitumen to the substrate. Asphalt derivative primers should
substrate dryness vary from being visibly dry to having a be used with asphalt and coal-tar derivative primers with
specific maximum moisture content. Since there is a lack of coal-tar bitumen.

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 C 981 – 05
8.3 Bitumens—Bitumens in a waterproofing system serve but superior to felts. It is of an open-mesh woven design and is
two functions. They provide the prime waterproofing compo- excellent where flexibility and adaptability to irregular sur-
nent of the system and the adhesive component for the faces, corners, and angles are a requirement. Woven cotton
membrane reinforcement. The bitumens used in plaza building fabric (Specification D 173) is saturated with asphalt or coal-
deck waterproofing are asphalt (Specifications D 312 and tar saturants.
D 449, Types I or II) or coal-tar pitch (Specification D 450, 8.4.3 Saturated Woven Jute—Saturated woven jute is an
Types II or III). In some instances these products are modified organic material, thus requiring the saturant to penetrate the
to serve a particular purpose. In building deck waterproofing, interstitial cells of the jute fibers. It is generally woven with
waterproofing grade asphalts and coal-tar pitches, as noted, are thicker thread than cotton, thus retaining a great quantity of
primarily used because of their cold-flow (self-healing) prop- bitumen. It has many of the same characteristics of cotton in
erties. relation to waterproofing. Woven jute fabric (Specification
8.3.1 Asphalt—Asphalt is derived from the residue of the D 1327) may be saturated with asphalt or coal-tar saturants.
process of manufacturing light petroleum distillates and further 8.4.4 Saturated Felts—Dry felts are organic mats saturated
processed into waterproofing and roofing grade asphalts. As- with saturating grade asphalt or coal tars. They provide a
phalts tend to be aliphatic, chain-like hydrocarbon compounds. container and reinforcement for the interply bitumen. They are
8.3.2 Coal-Tar Pitch—Coal-tar pitch is derived from crude of the same type used in roofing systems and are classified as
coal tar, a by-product from high temperature coke ovens, by a Specification D 226, Asphalt-Saturated (organic) and Specifi-
refining process of distillation and chemical extraction. Coal cation D 227, Coal-Tar-Saturated (organic).
tar pitches tend to be aromatic, ring-like hydrocarbon com- 8.4.5 Glass Fiber Felts—Glass fiber felts are light in
pounds.
weight. The glass fibers are dispersed at random to form a
8.3.3 Modified Bitumens—Modified bitumens (Specifica- sheet. The fibers may be continuous or in a jackstraw pattern
tion D 6152) are designed to develop a particular objective depending upon the method of manufacture and are bonded
such as extensibility, for example, viscosity variation, strength, together with resinous binder. Glass fiber felts are coated with
reduction of volatiles, and so forth. asphalt (Specification D 2178) or coal-tar pitch (D 4990).
8.3.4 Selection—The selection of bitumen type for a spe- 8.4.6 Asphalt-Coated Base Sheets and Coated Felts—
cific project is related to the numerous variables and options Asphalt-coated base sheets and coated felts, used as membrane
described in this guide and that must be taken into consider- reinforcement, consist of asphalt-saturated roofing grade felt
ation by the designer of the waterproofing system.
coated on both sides with coating-grade asphalt filled with
8.4 Reinforcements—The types of membrane reinforcement mineral stabilizer and finished on the top side with fine mineral
used in waterproofing are treated glass fabric, saturated woven surfacing. They are heavier and slightly stronger than saturated
cotton and saturated jute fabric, saturated felts, impregnated felts. Coated felts have less quantity of coating asphalt than
glass felts, and coated sheets. Specialty preformed sheets are coated base sheets. In cold temperatures a coated felt is difficult
also incorporated in plaza waterproofing. The requirements for to lay flat and avoid edge voids. The felts may be organic or
plaza deck waterproofing are complex. Thus, the designer inorganic. Asphalt coated glass fiber base sheet is described in
knowing his particular building problem must select the Specification D 4601.
membrane component types that will satisfy the design require-
8.5 Specialty Preformed Membrane—Modified-bitumen
ments. Combinations of the various membrane reinforcement
sheets (Specifications D 6162, D 6163, and D 6164), may
are commonly used in alternate plies, depending upon the
incorporate membrane reinforcement in single or multilayers
design requirement. Unless otherwise directed by the manu-
and be produced as a single preformed sheet.
facturer, asphalt bitumen should be used with asphalt-based
membranes and coal-tar bitumen with coal-tar based mem- 8.6 Flashing—The major flashing components for terminal
branes. conditions include fibrated troweling roofing cement, rein-
8.4.1 Treated Glass Fabric—Untreated glass fabrics are forced flashing felts, and proprietary elastomeric materials.
lightweight, inorganic, very high in tensile strength, open- 8.6.1 Bituminous Plastic Cement—Bituminous plastic ce-
mesh, and will not absorb water or any other material. As ment such as those meeting Specifications D 4022, D 2822,
finished treated products, (Specification D 1668, Type I As- D 4586 are made from (1) bitumen characterized as self-
phalt Treated, Type II Coal-Tar Pitch Treated and Type III healing, adhesive, and ductile; (2) compatible volatile solvents;
Organic Resin Treated), they provide excellent strength in and (3) mineral stabilizers mixed to a smooth uniform consis-
waterproofing and are particularly effective in areas of vibra- tency suitable for troweling applications.
tion, deflection, or where heavy loads are applied over the 8.6.2 Reinforced Flashing Felts—Plies used in flashings
waterproofing system. Their flexibility allows them to be used should be a material that is compatible with the waterproofing
in corners, in angles, and over irregular surfaces. Due to the membrane.
open-mesh woven design, they can be applied without entrap- 8.6.3 Proprietary Elastomeric Materials—Proprietary elas-
ment of air. tomeric materials based on neoprene (cured or cure-in-place),
8.4.2 Saturated Woven Cotton Fabric—Saturated woven butyl, and ethylene-propylene diene monomer (EPDM) may be
cotton fabric is an organic material, thus requiring the saturant set into hot bitumen or a cold-applied adhesive per manufac-
to penetrate the interstitial cells of the cotton fibers. It has good turer’s instructions. Application on roof cement may lead to
tensile strength, although not as strong as woven glass fabric solvent blistering and softening.

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 C 981 – 05
8.6.4 Selection—Unless otherwise directed by manufactur- system would have an “exposure” of 288 mm (111⁄3 in.) or 34
ers, asphalt-flashing materials should be used with asphalt divided by 3, and the “overlap” would be 627 mm (242⁄3 in.) or
membranes and coal-tar bitumen flashing materials used with 111⁄3 subtracted from 36. The extra 50 mm (2 in.) (36 minus 34)
coal-tar bitumen membranes. serves as a safety factor to assure that the vertical cross section
8.7 Handling and Storage—Proper handling, storage, and will contain the designated number of plies.
protection of waterproofing materials is essential. During 8.8.3.2 Ply-on-Ply (Phased Method)—“Ply-on-ply” or
application the presence of moisture, dirt accumulation, and “phased” construction is a method whereby each ply or group
damaged materials are primary causes of lack of bond, bond of plies are in a single-connecting layer over which the next
failure, and delamination. Since some waterproofing materials phase is applied. The phased method is often employed when
are susceptible to moisture damage and adsorption, optimum different types of membrane are used in the construction of the
storage and protection is in a weathertight enclosure. When job waterproofing membrane system. For example, a system of two
conditions make this unrealistic, materials should, as a mini- plies of felt plus two plies of fabric plus one ply of felt consists
mum, be stored off the ground or deck on pallets and covered in phase 1 of the application of two plies of felt in shingle
above, on all sides, and ends with breathable-type canvas fashion, in phase 2 of the application of two plies of fabric in
tarpaulins. Plastic sheets should not be used because they shingle fashion, and in phase 3 of the application of the final
permit condensation buildup under them. ply of felt with normal 50-mm (2-in.) single-ply overlaps.
8.8 Membrane Composition and Application—A built-up 8.8.3.3 Comparison of Methods—Shingle method advan-
bituminous waterproofing membrane consists of components tages over the phased method are (1) less potential for slippage,
joined together and bonded to its substrate at the site. Para- (2) less susceptibility to moisture entrapment, (3) greater
graphs 8.8.1-8.8.8.5 cover its composition and application on a potential for ply-to-ply adhesion, (4) reduction of potential
structural concrete substrate. See Section 12 for insulation slippage planes of bitumen, (5) any desired number of plies can
considerations. be laid in a single progressive operation, and (6) overall is a
8.8.1 Substrate Preparation—Surfaces to receive water- faster method. The phased method has an advantage over the
proofing must be clean, dry, reasonably smooth, and free of shingle method insofar as the operation permits a full layer of
dust, dirt, voids, cracks, laitance, or sharp projections before bitumen between the entire layer of membrane reinforcements
application of materials. Refer to Guide D 5295. providing a secondary waterproofing plane.
8.8.2 Primer Application—Concrete surfaces should be uni- 8.8.3.4 Placement of Plies—Membrane reinforcements
formly primed to enhance the bond between the membrane and should start at the low point of the deck working to the high
the substrate, and thus inhibiting lateral movement of water. level so that the direction of the flow of water is over the lap.
The primer must not be left in puddles. The normal application All plies should be firmly embedded into the hot bitumen by
rate is 0.3 L/m2(3⁄4 gal/100 ft2). Asphalt Primer (Specification brooming, pressing, or other suitable means so that ply shall
D 41) should be used with asphalt bitumen. Coal-tar primer not touch ply and to prevent formation of wrinkles, buckles,
(Specification D 43) should be used with coal-tar pitch bitumen kinks, blisters, or pockets. After plies are in place, the surface
unless waived by the manufacturer of the membrane for the of the membrane system should be coated with hot bitumen
particular project conditions. Primer should be allowed to and while still hot, a sheet of protection board embedded (see
become tacky or dry before application of bitumen. A wet Section 9). Only an area of size that will allow completion of
primer may soften the bitumen. the membrane and placing of protection board upon the
8.8.3 Position and Composition of Membrane Plies—The membrane in one working day should be undertaken; exposure
number of plies of membrane reinforcement required is depen- of membrane reinforcing plies to weather, dew, condensation,
dent upon the head of water and strength required by the design or frost can result in membrane failure. Consideration of
function of the wearing surface. Plaza deck membranes should bitumen flow or creep merits attention to temperature gradients
be composed of not less than three plies. The composition of and the estimated maximum temperature of the membrane in
the membrane is normally of a “shingle” or “ply-on-ply” the deck system. The slope of the substrate and membrane
(phased) construction. should also be considered.
8.8.3.1 Shingle Method—The “shingle” method is achieved 8.8.4 Bitumen Application and Quantities—The layer of
by successive lapping of one ply over another, using prescribed bitumen between plies of the membrane reinforcement should
overlaps, until the required number of plies of membrane not be excessive. The maximum bond strength is achieved with
reinforcements are achieved. For example, a four-ply system is the thinnest practical, continuous application of bitumen be-
achieved by lapping each successive ply slightly over three tween the plies. There should be sufficient bitumen to penetrate
quarters of the previously laid ply. Based upon a 914-mm the membrane reinforcing in addition to that required to
(36-in.) wide membrane reinforcement, each ply overlap is provide adhesion properties. The criterion is to apply a
approximately 699 mm (271⁄2 in.), leaving a 216-mm (81⁄2-in.) sufficient quantity of bitumen to provide a full and continuous
exposure to the weather. To determine the amount of ply course of bitumen for embedment of each subsequent ply of
exposed to the weather, using a 914-mm (36-in.) width as a membrane reinforcement. The quantities to achieve this may
base, divide 864 mm (34 in.) by the number of plies. The vary from 0.83 kg/m2 (17 lb/100 ft2) to 1.47 kg/m2 (30 lb/100
resultant is the exposure to the weather. To determine the ft2) for each course of bitumen between membrane plies.
overlap distance, subtract the exposure obtained from the width Differences in rates may result from atmospheric conditions,
of the 914-mm (36-in.) wide roll. For example, a three-ply method of application, and temperature at actual time of

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 C 981 – 05
placement. As the bitumens flow less readily at lower applica- bitumen through the joint. Where movement is anticipated,
tion temperatures, the interply layer of bitumen tends to be these joints should be designed as expansion joints (see 8.8.7).
higher in weight. The quantity may also vary depending upon 8.8.7 Treatment at Expansion Joints—There are basically
the speed the applicator moves mechanically operated two concepts that could be considered in the detailing of
bitumen-spreading equipment. These variations are not neces- expansion joints at the membrane level of membrane water-
sarily troublesome provided the bitumen is hot enough to proofing systems. These are (1) the positive seal concept
develop adhesion to the membrane reinforcement, and the directly at the membrane level, or (2) the water shed concept
interply weights are not excessive or so low as to prevent with the seal at a higher level than the membrane. Where
continuous bond. The use of excessive quantities of bitumen in additional safeguards are desired, a drainage gutter under the
areas subject to horizontal and vertical loads should be joint could be considered (see Fig. 2). Flexible support of the
avoided. For estimating purposes, an average quantity of membrane is required in each case. Expansion joint details
bitumen between plies of membrane reinforcement may be should be considered and used in accordance with their
classified as 1.13 kg/m2 (23 lb/100 ft2) for asphalt and 1.22 movement capability.
2
kg/m (25 lb/100 ft2) for coal-tar pitch. Glass felts may require 8.8.7.1 Positive Seal Concept—The positive seal concept
greater quantities of interply bitumen due to the interstices of entails a greater risk than the water shed concept since it relies
the reinforcement. Use manufacturer’s recommendations to fully on positive seal joining of materials at the membrane
ascertain quantities of bitumen required. level, where the membrane is most vulnerable to water
penetration. The materials used, and their joining, must be
8.8.4.1 Application Temperature—For the proper applica- carefully engineered by the manufacturer of the bituminous
tion of bitumen in a built-up bituminous membrane, it is membrane waterproofing system, and subsequent field instal-
important to note that bitumen is a water-resistant, viscous lation requires the best of workmanship for potential success,
adhesive that depends upon flow for its adhesive and wetting leaving no margin for error. Therefore, use of this concept is
properties. Bitumen flow is best measured by the viscosity of not recommended.
the material. Viscosity changes with temperature; the higher 8.8.7.2 Water Shed Concept—The water shed concept, al-
the temperature the lower the viscosity. (1) Asphalts—Studies though requiring a greater height and more costly concrete
have shown that asphalts having a viscosity from 100 to 150 forming, is superior in safeguarding against leakage, having the
cSt (0.0001 to 0.0002 m2/s) have optimum wetting and
adhesive properties. The optimum application temperature of
asphalt is the “equiviscous temperature,” the temperature at
which asphalt will attain a target viscosity of 125 cSt (0.0001
m2/s), at the point of application. A tolerance range of 625°F
(63.9°C) is added for practical application in the field to
accommodate the effects of wind chill, sunshine, or ambient
temperature. Asphalt should not be heated to or above the
actual Cleveland Open Cup (COC) flash point or heated and
held above the finished blowing temperature for more than 4 h.
(2) Coal Tar Pitches—Studies have shown that coal tar pitches
have a viscosity from 12 to 32 cSt or 15 to 40 centipoise have
optimum wetting and adhesive properties. The optimum appli-
cation temperature of coal tar pitch is the “equiviscous tem-
perature,” the temperature at which coal tar pitch will attain a
target viscosity of 20 cSt or 25 centipoise at the point of
application. A tolerance range of 625°F (613.9°C) is added
for practical application in the field to accommodate the effects
of wind chill, sunshine, or ambient temperature. Coal tar pitch
should not be heated to or above the actual Cleveland Open
Cup (COC) flash point.
8.8.5 Treatment at Reinforced Joints—Over the reinforced
structural slab joints, one ply of 6-in. wide membrane rein-
forcement embedded in products like bituminous plastic ce-
ment (Specifications D 2822, D 4056, or D 4022) (see also
8.6.1) should be applied before application of the bituminous
membrane.
8.8.6 Treatment at Nonreinforced Joints—Nonreinforced
joints between the structural slab (membrane substrate) and
vertical surfaces that are not subject to movement should
receive a bead of compatible sealant in a recessed joint before FIG. 2 Schematic Expansion Joint Concepts at Membrane Level
application of the membrane to reduce potential leakage of (see 8.8.7)

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 C 981 – 05
advantage of providing a water dam at the membrane level. receive waterproofing must be in accordance with Section 7.
The joining of differing materials can then be placed at a higher Masonry surfaces to receive flashings should be primed before
level and treated somewhat in the manner of counterflashing, application of the flashing (see 8.2). Corners must be designed
hence the term “watershed concept.” However, if a head of to allow easy installation using hand tools with consideration
water rises to the height of the material joined, this concept of the required system and type of flashing material suitable to
becomes almost as vulnerable as the positive seal concept. the installation. Anchorage of the terminal edge of the mem-
Therefore, drainage is recommended at the membrane level brane system is essential (see Figs. 6-8). Hot bitumen should be
and is further analyzed in Section 10. applied sparingly at terminal conditions. Temporary termina-
8.8.7.3 Provision for Movement—Generally, expansion tions of flashing must be provided at the end of each workday
joints in a structural slab are seldom less than 30 m (100 ft) to prevent water infiltration and loss of bond. The surface of
apart and may be as much as 91 m (300 ft) or more apart. flashing should be protected by protection board cover against
Therefore, relatively large amounts of total movement are to be construction damage.
dealt with, generally in the range from 13 mm (1⁄2 in.) up to 38 8.8.8.1 Transitional Changes in Membrane—Reinforce all
mm (11⁄2 in.). Maximum movement generally occurs during the intersections with walls, corners, or any location that may be
construction phase before insulation and wearing course are subject to unusual stress, with two layers of woven fabric
installed over the membrane, but the joint should be detailed embedded in hot bitumen. Extend the fabric onto the deck at
for maximum movement at any time. Gaskets and flexible least 150 mm (6 in.) and extend up the wall the full height to
preformed sheets are required to absorb such amounts of the wearing surface, carrying fully into corners. Woven fabrics
movement inasmuch as bituminous membranes have little or are employed in this initial preliminary phase because of their
no movement capability. Since such materials, when used at an inherent flexibility and because they easily conform to a 90°
expansion joint, must be joined to the bituminous membrane, juncture. Felts and coated sheets do not easily conform to a 90°
the watershed concept should be used. Figs. 3-5 indicate bend. Cants, when required by the membrane manufacturer,
expansion joints using the watershed concept that have a should be cementitious and formed approximately 75 by 75
movement capability of 69 mm (3⁄8 in.) when installed in a mm (3 by 3 in.).
designed concrete opening of the width indicated. These details 8.8.8.2 Terminal Flashing Above Membrane—Flashing
could be increased in movement capability with a larger gasket membranes should extend above the wearing surface and the
and concrete opening if so desired. highest possible water level and not less than 150 mm (6 in.)
8.8.8 Transitional Changes and Terminal Conditions— onto the deck membrane. Flashing bitumens and reinforce-
Transitional changes and terminal conditions should be de- ments must be compatible with the deck membrane. These
signed for simplicity of installation and repetitive operations normally consist of a number of plies not less than that of the
and normally consist of composite sheets of felts, fabrics, and deck membrane and are tapered from flashing membrane
bitumens with a mineral surface. Square corners, sharp edges, thickness to the terminal edge at the top where they are secured
and smooth planes are not adaptable to bitumen and bitumen to the substrate by nailing or by a horizontal transition. The
reinforcements. The functional effectiveness results from de- terminal edge should be covered by metal counter or through
sign simplicity of the field installation, consideration of loca- wall flashing. Where the terminal edge is nailed to a wood
tion, handling, similarity of details, material selection, and nailer, greater protection is provided by stripping over the
method of placement. Bitumens and reinforcing must be nailed edge before covering with protection board and the
compatible with the membrane and substrate. Surfaces to metal counter flashing. The latter serves only as a watershed

FIG. 3 Water Shed Concept Expansion Joint (see 8.8.7.2)

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 C 981 – 05

FIG. 4 Water Shed Concept Expansion Joint (see also 8.8.7.2 and Fig. 5 for Easier Gasket Installation Detail)

FIG. 5 Water Shed Concept Expansion Joint (see also 8.8.7.2 and Fig. 4)

and protection against construction damage or subsequent 8.8.8.3 Terminal Flashing Below Membrane—Turndown
damage when it becomes vulnerable to finish wearing surface flashing of membranes must be treated similarly to turnup
maintenance or physical abuse. Where the metal counterflash- flashing, and of similar materials. The flashing should extend
ing can be punctured, torn, or easily cut and damaged, it is over the wall dampproofing or membrane waterproofing not
advisable to provide additional protection board over the face less than 100 mm (4 in.).
during construction and placement of the wearing surface (see 8.8.8.4 Termination at Drain—Drains must be provided
Figs. 6-8). Fig. 6 shows how protection is provided above the with a wide metal flange or base and set slightly below the
finish wearing surface and against physical damage from drainage level. Metal flashing for the drain, if required, and the
maintenance of the wearing surface. Fig. 7 shows how protec- clamping ring should be set on the membrane in bituminous
tion is not provided as well as in Fig. 6 since the terminal edge plastic cement. The metal flashing is stripped in to provide the
is below the finish wearing surface but provides for simpler primary seal at the periphery of the joint between the metal
construction. Fig. 8 shows where a masonry or similar facing flashing and the membrane. The stripping consists of a mini-
material is used above the finish wearing surface over a mum of two plies of membrane reinforcement and three
horizontal concrete ledge. applications of bituminous plastic cement (see Fig. 9).

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 C 981 – 05

FIG. 6 Terminal Condition Above Finish Grade on Concrete Wall FIG. 8 Terminal Condition with Masonry Above Finish Wearing
(see 8.8.8 and 8.8.8.2) Surface at Grade (see 8.8.8 and 8.8.8.2)

struction. Protection board should be applied after the mem-

brane is installed. The board also serves to protect the
membrane from damage due to movement and penetration of
materials above after the deck construction is complete. Pro-
tection board should be placed on the waterproofing membrane
as soon as possible after flood testing and any necessary repairs
have been completed. Refer to Guide D 6451 for protection
board installation guidelines.

10. Drainage System

10.1 When the membrane waterproofing is covered over
with a wearing course, it is necessarily assumed that water can
and will reach the membrane. Otherwise, the membrane below
the wearing course would not be needed. Drainage should then
be considered as a total system from the wearing surface down
FIG. 7 Terminal Conditions on Concrete Wall Below Finish to the membrane. The design of the drainage sub-system
Wearing Surface at Grade (see 8.8.8 and 8.8.8.2) should be determined considering the probable interior and
exterior temperatures, and the rainfall both direct and that
8.8.8.5 Termination at Penetrations—Penetrations through which is wind diverted by adjacent structures. The wearing
the membrane such as conduits and pipes should be avoided course may consist of such materials as stone, brick or tile,
whenever possible. Penetrations must be flashed to a height asphalt paving or blocks, and concrete, either as a finish or as
above the anticipated water table that may extend above the a substrate for the above finish materials. Some of these
wearing surface. Proprietary devices are available, which will materials can absorb varying amounts of moisture that may
allow for pipe movements and which provide for the necessary cause some to rapidly deteriorate if subjected to freezing
flashing to be knit into the membrane similar to the drainage temperatures. The plaza drainage system should be designed to
fitting. It is desirable to cant the surface of the substrate upward minimize cyclic saturation of the wearing surface and its
to lift the flashing above the surface of the membrane and thus substrate. Since it would be undesirable to permit water to
apply the watershed principle (see Fig. 10). build up below the wearing surface, multilevel drains should be
used with particular emphasis on rate of flow into the drain at
9. Protection Course the membrane level. Basically, the drainage system is analyzed
9.1 The built-up bituminous membrane should be protected for functioning both at the membrane level and at the wearing
from damage before and during remainder of the deck con- surface.

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 C 981 – 05

FIG. 9 Termination at Drain (see 8.8.8.4)

10.2 Need for Drainage at Membrane Level—It is essential 10.3.5 Use multilevel drains capable of draining all layers of
that water be removed from the membrane level for the the building deck. The drain should have an integral flange at
following reasons: least 50 mm (2 in.) wide for adherence and bonding with the
10.2.1 To avoid building up a pressure head against the concrete slab and to provide for termination of the built-up
membrane and particularly against the more vulnerable splices bituminous membrane with sufficient room for an adhesive
and joints in the system. bond. The flange should be set level with the structural slab
10.2.2 To avoid freeze-thaw cycling of trapped water that surface.
could heave and disrupt the wearing course. 10.4 Drainage at Wearing Surface—Drainage at the wear-
10.2.3 To minimize the deleterious effect that prolonged ing surface is generally accomplished in one of two ways: (1)
undrained water could have on wearing course materials. by an open-joint system permitting most of the rainwater to
10.2.4 To minimize thermal inefficiency of wet insulation penetrate rapidly down to the membrane level and subsurface
and of water under the insulation. drainage system, or (2) by a closed-joint system designed to
10.3 Recommendations for Proper Drainage at the Mem- remove most of the rainwater rapidly by slope-to-surface
brane Level: drains and allowing a minor portion to gradually infiltrate
10.3.1 Slope the monolithic concrete substrate under the down to the membrane level. Either system may be used over
membrane a minimum of 2 % (1⁄4 in./ft). a lower-level membrane, the choice generally being governed
10.3.2 Slope the monolithic concrete substrate under the by the materials desired for the wearing course. In each case,
membrane to drain away from expansion joints and walls. provision should be made to permit inspection and mainte-
10.3.3 Use a drainage course to increase the rate of flow to nance of drains.
drains. 10.4.1 Open-Joint System—The vertical joints in the hori-
10.3.4 Avoid undrained pockets such as downward loops of zontal wearing course could be left open (unsealed) provided
flashing into expansion joints. the joints are less than 6.3 mm (1⁄4 in.) wide and do not present

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 C 981 – 05

FIG. 10 Termination at Pipe Penetrations (see 8.8.8.5)

a walking hazard, and if proper drainage is provided at the methods should be carefully considered. Another design prob-
membrane level. This is generally accomplished by what is lem presented by open joints in the wearing course is the
known as a “pedestal system” described in 10.4.1.2. possibility of inducing condensation on the interior ceiling of
10.4.1.1 Advantages and Disadvantages—An open joint the space below the plaza deck. This potential problem can be
eliminates the cost and maintenance of sealant joints and minimized by placing the insulation as close to the waterproof-
compression seals. With this construction, precipitation and ing membrane as possible so that cold water is not continually
water from melting snow are discharged into the drainage void taking the heat out of the structural slab.
through the open paver joints. From there it drains over the 10.4.1.2 Pedestal System—Pedestals are used to support
surface of the insulation. That which reaches the membrane relatively large areas of such materials as precast concrete
follows the insulation-joint drainage channels through second- slabs, stone slabs and prefabricated masonry. The space below
ary drainage perforations in drains at the membrane level. the wearing course is left open and the varying height is
Another advantage is that the wearing surface can be designed accommodated by adjusting the height of the pedestals. Al-
to be level, but it is advisable for each individual panel to have though left open, the joints should have resilient spacers to
a slight crown upward at the center to avoid possible ponded avoid problems of creeping or shifting panels. In a design
water for a period of time after a rainfall. An option would be where pedestals are intended to bear directly on the protection
a weep hole in the center of each panel. A disadvantage is the board, the designer of the system should consult the membrane
problem of debris that can collect in the joints and in and protection board manufacturers and determine that the
subsurface drains. In the deck design, drain maintenance imposed loads will not have damaging effects on the membrane

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 C 981 – 05
and protection board under the service conditions anticipated. 12. Insulation
The amount of compression deflection expected should also be 12.1 General—The selection of insulation, its quantity, and
analyzed as to the possibility of creating uneven settlement of location in the system are influenced by the design of the deck
the wearing course panels. The open joint system is not well system, the total environment under which it may be required
suited to areas subject to frequent vehicular traffic. Consider- to function, the physical or chemical properties, or both, of
ation should be given to the possible damaging effects on the available insulating materials, the nature of the wearing course,
membrane and protection board caused by initial installation of and the loads to be supported. Each of these finish components
pedestals as well as subsequent traffic, emergency vehicles, or will result in a small difference in the total heat resistance of
thermally induced lateral loads transmitted to the pedestals this system and the dew-point locations for the changing
from the wearing course panels. In no case should the pedestals seasons, all of which relate to the membrane location within
be placed directly on the membrane. Extruded polystyrene the total system. A graphic analysis of the temperature gradient
(Specification C 578, Type VI) is typically used when pedestals between the wearing surface and the interior should be made in
are to rest directly on the insulation. Depending on the order to determine the location of the dew point and its effect
compressive strength requirements, Specification C 578 Types upon the total system and in regions of low temperature, the
IV, V, and VII may also be used. effect upon the drainage system. See Practice C 755 for
10.4.2 Closed-Joint System—A closed-joint system is nor- temperature and dew point determination method.
mally used with a wearing course of relatively small prefabri- 12.1.1 Temperature and Humidity Gradient—Temperature
cated units, impractical to support on pedestals, or with larger and humidity gradients must be determined to check a system
areas of cast-in-place concrete. Dynamically moving joints in for location of dew point and temperatures of components, that
such systems are filled with sealant or compression seals. The is, membrane, drainage course, and surfaces (see Fig. 1). This
wearing course materials are relatively impermeable. The is influenced by such factors as:
wearing surface is sloped to drains, but provisions should be 12.1.1.1 Type of occupancy of the space below the system.
made for the infiltration of water to the membrane level and the 12.1.1.2 Heat loss and heat gain restrictions.
subsurface drainage system. 12.1.1.3 Temperature and humidity levels to be maintained
in the underlying occupied space.
11. Drainage Course
12.1.1.4 Climatic pattern (temperature extremes), sharpness
11.1 Recognizing that water may infiltrate below the wear- and frequency of thermal cycling, nature and amount of
ing course to be carried off on top of the membrane to the precipitation, ambient humidity pattern, degree and prevalence
drains, a drainage course of washed, round gravel should be of sky cover, and exposure of the affected area.
provided above the protection board, over the built-up bitumi- 12.1.1.5 Drainage pattern of design (over sloped surface to
nous membrane. This permits water to filter to the drain and drains), percolation through system to membrane-covered
provides a place where it can collect and freeze without substrate to drain, and combination of over-the-surface drain-
potential damage to the wearing course. If concrete is placed as age and percolation to membrane-covered substrate.
the wearing course, a minimum 0.1 mm (4 mil) perforated, 12.1.1.6 Nature of wearing course (composition, unit size,
polyethylene layer should be placed over the drainage course to pattern and stabilization), and
prevent concrete from filling the drainage course voids. Also,
12.1.1.7 Relationship to adjacent structures (the reflection
the drainage course should be stabilized if the deck is to of radiant heat from an adjacent building (adds materially to
withstand vehicular traffic, because of the likelihood of lateral the heat gain by direct exposure to solar radiation)), the
shifting under thrust, even without vehicular traffic, if free to cascading water of a heavy, wind-driven rain down the face of
move laterally on a sloping surface. One method of stabilizing such a building increasing the flow on adjacent plaza drainage
aggregate, while still maintaining its percolation characteris- system.
tics, is to use a controlled amount of epoxy binder, thoroughly
12.2 Properties Affecting Performance—The only real basis
mixed with the aggregate before installation. The quantity to be
for the determination of the performance of an insulation in
used is related to aggregate size and gradation. Several
plaza service is the spectrum of its physical properties, which
proprietary binders are available, and the manufacturer’s in-
are basic to the specific performance requirements of the
structions should be followed regarding their use and installa- insulation in the plaza system under the total ambience in
tion. A cement binder is also used for this purpose in a material which the insulation will be required to function. Such prop-
known as no-fines concrete. Sufficient binder is necessary to erties must be based upon tests, and be expressed in terms,
stabilize the aggregate, but an excessive amount could overly which accurately reflect the service conditions which will be
restrict drainage through the voids that could become clogged imposed upon the insulation in the specific plaza service. There
with fine, loose particles. The drainage course aggregate should is a dearth of testing procedures and significant catalog
be washed, round river gravel conforming to gradation size no. information that are essential to intelligent choice of insulation.
8 in accordance with Specification C 33. However, such lack does not negate the crucial importance of
11.2 If a prefabricated drainage composite is used under basing the choice of insulation on the whole spectrum of
vehicular traffic, it is important to select a type that can bear pertinent physical and chemical properties of the insulation in
traffic loads. light of the totality of service requirements.

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 C 981 – 05
12.2.1 Coeffıcients of Thermal Expansion—Insulations that any substances that can serve as nutrients. Vegetable fiber
will be located near the wearing surface should be character- insulation cannot be used indiscriminately.
ized by low coefficients of thermal expansion. This becomes 12.2.5 Freeze-Thaw Resistance—In those designs that lo-
increasingly important with increase in the range of thermal cate the membrane between the insulation and the wearing
cycling. When the membrane is over the insulation, and where course in climates that include below freezing temperatures,
it must provide dimensional stability in the face of rather large any moisture in the system will tend to move toward the
temperature changes, a low coefficient is essential. It cannot be underside of the membrane during cold weather. A relatively
ignored at any time when the insulation is close to the wearing closed-cell cellular insulation with inelastic walls such as
surface. foamed concrete or cellular glass is vulnerable to freeze-thaw
12.2.2 Moisture Sensitivity—Insulations that will be in the damage under these conditions, especially at the insulation/
path of water vapor movement, which are permeable to water membrane interface. The cell walls of any cellular insulation
vapor and which will be subjected to temperatures to condense that shall be used must be flexible and resilient with the
this water vapor, must be dimensionally and structurally volumetric changes accompanying the cylic freezing and
unaffected by the presence of internal water or use of a vapor thawing of water.
retarder is required. In situations where insulations would be 12.2.6 Thermal Resistance—The thermal resistivity of the
subjected to internal-condensing conditions, the impact of such insulation must be such that the thickness required to provide
water content upon thermal resistance of the insulation must be the necessary total thermal resistance can be accommodated in
recognized. Insulations that are likely to be in substantial the available space. The amount of insulation required is
contact with free water in the drainage system should be as determined by desired heat loss and heat retention character-
hydrophobic as possible. Also, the less water- and vapor- istics. Under the full range of occupancy, temperature and
permeable and hygroscopic they are, the better they will serve. humidity levels, the temperature of the deck must remain
The presence of such water as it accumulates should have above the dew point of the building air. Generally, insulation
minimal effect upon dimensional, thermal, and structural tends to lose some thermal resistance as it ages.
properties, and service life. Moisture-related dimensional 12.2.7 Compatibility—Care must be exercised to be sure
change not only affects the stability of the insulation, as an that the insulation and other materials in the system with which
element in the structural composite, but it also has an effect on it is in contact are compatible. This is especially important
the maintenance of drainage channels that consist of open when polymeric materials are used.
jointing of the insulation. The disposition to hold in suspension 12.2.8 Compressive Strength, Deflection, and Yield—
such water as is internally condensed, instead of permitting its Compressive strength is determined by the dead load and the
free flow to drains has an impact upon thermal resistance and range of live loads to which it will be subjected and recovery
accelerates the degradation of most insulations. Important also, from compression loads. Substrates are seldom perfectly pla-
is the degree to which the insulation absorbs and holds free nar. Insulation must not be fractured by profile irregularities.
water. The typical plaza system is seldom dry, almost always The ability to conform under compression or yield in flexure
contains free water, and is subjected to flowing water in before fracture should be considered in selection of insulation.
quantity. Insulation with a hydrophobic character is an advan- 12.2.9 Shear Strength—Strength in shear should be consid-
tage. The constituents of the insulation should not be softened ered for designs in which the insulation will be required to
or degraded by water, and the adhesives and bonding agents transmit the shear stresses imposed by horizontal thrust of
used in its structure should not lose their bond strength under traffic to its substrate and in turn be transmitted to the structural
conditions of persistent wetness. slab. Unitary pavers and thermoplastic asphalt paving impose
12.2.3 Load Resistance—Insulations must be selected in such stresses upon the insulation, the magnitude of which are
full recognition of their long-term ability to withstand pro- determined by the type of traffic.
jected loads. Compressive strength should be determined for 12.2.10 Fatigue Stress—Fatigue under imposed cyclic com-
periodic durations of loads at temperatures that are realistically pression loading and structural relaxation should be considered
representative of possible service conditions. Insulations to be for its effect upon durability.
used under traffic that involves horizontal thrust must possess 12.2.11 Dimensional Stability—Dimensional changes and
the necessary strength in shear as well as in compression. In the stability are influenced by the coefficient of thermal expansion
event that an excessive vertical load is applied to an area of and moisture sensitivity (see 12.2.1 and 12.2.2).
insulation, it is necessary that such a load should not fracture or 12.2.12 Vapor Permeance—Vapor permeance is significant
unrecoverably deform the insulation. System design must only for systems that place the insulation on the underside of
make ample provision for distributing concentrated loads. the structural slab.
Where vehicular traffic is anticipated, effects of fuel, oil, 12.2.13 Depolymerization—All synthetic polymers undergo
ethylene glycol, and ice-melting materials on the insulation depolymerization that is a joint function of the molecular
should be investigated. structure, time, and temperature. There are great differences
12.2.4 Fungus Resistance—Insulations should contain no between the polymers in their rates of depolymerization.
nutrients for fungi, vermin, insects, or other organisms. Most 12.3 Location Analysis—Basic to the location determina-
insulated waterproofing systems will contain enough moisture tion is the humidity pattern of the occupancy. In the case of
to encourage growth of these organisms in the presence of high humidity occupancy, in temperature climates with cold
nutrients. Fungi are sure to be active if the insulation contains winters, it is important that the insulation be so located as to

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 C 981 – 05
protect the membrane from the thermal effects of outside insulation of low permeance, but to surface it with a very low
temperatures. Otherwise, there will be condensation on the permeance vapor retarder. However, the free-water content of
underside of the membrane under winter weather conditions the concrete remains high when the plaza system is con-
(see Fig. 1). The temperature/humidity pattern in warm cli- structed, and the normal construction schedule makes no real
mates, where air conditioning is employed for much of the provision for the effective drying out of the structural deck
year, (where winters are mild) and to the extent that the slab. It would therefore be inadvisable to sandwich the con-
membrane temperature reflects building interior temperature crete between the membrane and the vapor retarder. It could be
and the membrane temperature falls below the dew point of years before the heavy excess of water in the concrete would
ambient air, there will be condensation on the exterior side of have been released. In the meantime, the excess water would
the membrane. If insulation is so located as to permit conden- be concentrated in the concrete under the membrane all winter
sation at the membrane, provision must be made for the free long where it would be subject to freezing and thawing. In
flow of the resulting water to drainage. Winter in a warm summer it would be concentrated in the insulation at the vapor
climate presents few of the problems and eliminates most of retarder. To omit the vapor retarder would progressively add to
the moisture-related problems that characterize temperature the water content of the concrete during the winter. In warm
zone design. There are occasions when the choice of insulation climates, this problem is not encountered. During the entire
type is primary to the design. Taking into account the condi- air-conditioning season, the vapor drive is from the membrane
tions of occupancy and climate, the water sensitivity and underside toward the low-vapor-pressure interior. Without a
permeability of the insulation will determine its proper location vapor retarder, the concrete is effectively dried out during the
in the plaza system. first air-conditioned summer of occupancy. A vapor retarder
12.3.1 Placement Below Structural Slab—Insulation placed here would have negative value except in instances of unusu-
below the structural slab subjects the membrane to maximum ally high humidity winter occupancies. In general, the appli-
thermal cycling. Membrane temperature will be affected cation of insulation below the structural deck should be limited
largely by outside ambient air temperatures, modified only by to warm climates and to low-humidity occupancies in temper-
(1) solar radiation absorption, (2) nighttime radiation from the ate climates.
interior to a clear sky, (3) distance of the membrane below the 12.3.2.3 Use of Ventilated Plenum Between Insulation and
exposed surface, (4) runoff of melting snow or cold summer Slab—Under one design condition, the disadvantages in
rain, (5) the heat capacity of the overlying system, and (6) the 12.3.2.2 (Vapor Retarder Requirements) are eliminated. This is
degree of openness in the overlying system. Unless ambient one in which a ventilated plenum is located between the
conditions and cure time have been such as to permit the structural deck and ceiling and outside air is force-circulated
evaporation of essentially all the uncombined water in the through it during the entire heating season. In this system, the
concrete, insulation cannot safely be applied to the underside ceiling must incorporate an effective vapor retarder. Atop the
of the deck. In such construction, if winter damage to slab and ceiling, continuous insulation such as batt or loose type, is
membrane is to be avoided, water vapor from a heated placed in thickness to provide desired total resistance. During
occupied space cannot be permitted to reach the underside of the air conditioning season, the ventilation system is closed off
the membrane, nor the structural deck. Therefore, either a tightly. This system could thus eliminate insulation wetness,
vapor retarder on the underside of the insulation or a highly freeze-thaw problems, and concrete-drying-out problems.
impermeable insulation system would be required. However, 12.3.2.4 Suitable Insulation Types—For most applications,
this method would lock the concrete’s free water in the deck flammability and smoke potential are foremost among selec-
where it would promote both concrete freeze-damage and tion considerations. This rules out use of most organic foams
membrane deterioration. If insulation must be applied to the and insulations containing a large proportion of organic fibers.
underside of the structural deck, the concrete must be dry and
12.3.3 Placement Between Structural Slab and
the insulation vapor-tight. In freezing weather, any drainage
Membrane—Location of insulation between structural slab and
channels above the membrane are vulnerable to damage.
membrane requires that the insulation serve as a structurally
12.3.2 Principles Governing Selection for Placement Below sound substrate for the membrane and a laterally stable base for
Structural Slab: the wearing course and its traffic loads. The wearing course
12.3.2.1 Fire Code Requirements—When insulation is ap- must also be effectively laterally stabilized. Few insulations
plied to the underside of the deck, its fire resistance and would serve as satisfactory substrates for a membrane for even
high-temperature behavior are important considerations. occasional vehicular traffic unless the wearing course is effec-
Newer fire code requirements substantially rule out the more tively laterally stabilized. This design can prevent condensa-
adaptable insulations in this service. The approvable inorganic tion in or on the underside of the structural deck if total thermal
spray-on materials are of comparatively low thermal resis- resistance of the system overlying the deck has been deter-
tance, are highly permeable to vapor, and tend to be somewhat mined in the light of possible minimum outside temperatures.
water sensitive. However, moisture will accumulate in the sandwich during
12.3.2.2 Vapor Retarder Requirements—In temperate cold weather to the extent of the free water in the concrete, the
zones, for all but the driest of occupancies, water vapor will be magnitude and duration of vapor pressure differential between
driven through the insulation and structural deck to the occupancy and the underside of the membrane and the net
membrane during most of the hours of the heating season. permeance of the deck/insulation composite. This may be
Normally, it would be advisable not only to employ an augmented by membrane or flashing discontinuities and by

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 C 981 – 05
moisture that entered during construction. As long as weather system makes possible a level, wearing surface in an open-joint
conditions are such as to keep the temperature of the membrane system without surface runoff by providing for quick percola-
below that of the top surface of the structural deck, this tion to a sloped-to-drain structural deck. Under these circum-
moisture will be held in the upper part of the sandwich if the stances the insulation, laid with butted joints for drainage
insulation is capable of holding it capillarily. When weather through them, is applied over the membrane. An effective
moderation reverses the temperature differential, the free water watershedding drainage system must be provided to prevent
will move into contact with the deck. This can result in a such water from becoming residual. A variation of this con-
generally wet deck unless occupancy conditions are such that struction is the placement of the insulation atop a well-
the free water will be evaporated before it reaches the stabilized coarse-aggregate drainage system placed over the
underside of the deck by capillary action. If the membrane is to membrane (see Section 11). Under this design, the wearing
be placed on the top (weather side) of insulation, a temperature surface is sloped to drain and has sloped secondary drainage at
and humidity gradient should be calculated between the the membrane level. The drainage course under the insulation
occupied area and the wearing surface to determine the must be completely stable in itself to ensure the structural
necessity of providing a vapor retarder between the structural stability of the insulation-wearing course composite. If a
slab and insulation. If a hot-applied bituminous vapor retarder reinforced concrete slab is cast over the insulation for protec-
is required under the insulation, it shall be turned up at its tion and wearing course, or protection and substrate for the
perimeter and made continuous with the waterproofing mem- wearing course, it should be sloped for drainage and stabilized
brane system. It is recommended that the insulation chamber against displacement other than for thermal movement.
be provided with drainage. If a cold-applied vapor retarder is 12.3.6 Principles Governing Selection for Placement Be-
considered, investigate compatibility, attachment, and adhesion tween Membrane and Wearing Course—To the extent that the
with substrate and insulation. When thermal insulation is to be design is such that it brings the insulation into frequent contact
used below the membrane, embed it in a full and continuous with water, it should be correspondingly water-insensitive. It
application of hot bitumen applied to the primed concrete deck should effectively resist water entry under prolonged immer-
or to the vapor retarder. In light of the moisture migration sion and persistent wetness. If no pedestal-void or coarse-
mechanism inherent in this design, when employed in climates aggregate drainage course separates it from the wearing course
which include near freezing temperatures, several purposes composite, it should be as thermally stable as possible because
would be served by the use of vapor retarders on the top of the sharp thermal cycling to which its surface will be
surface of the structural deck. If the vapor retarder membrane subjected. Full account should be taken of any horizontal-
is open to the drains serving the upper primary membrane, the thrust stresses to which it will be subjected in service.
second lower membrane could serve to (1) drain leakage of the 13. Protection or Working Slab
primary membrane, (2) sharply restrict the entry of vapor from
occupancy into the sandwich, (3) release to drain openings 13.1 A major problem in the waterproofing of building
much of any vapor that does penetrate into the sandwich, and decks is that the waterproofing is usually required early in the
construction phase so that finishing materials could be installed
(4) prevent moisture condensed within the sandwich from
in the occupied spaces below. In larger structures, construction
entering the structural slab. In the event that such a second
may continue long after waterproofing of the adjacent building
membrane is employed, it becomes especially important that
deck is required. Storage of materials as well as vehicular and
the underside of the structural deck be and remain free and
pedestrian traffic can impose an intolerable strain on a mem-
unfinished until the deck has lost nearly all of its free water.
brane covered only with protection board (see Section 9). A
12.3.4 Principles Governing Selection for Placement Be- concrete slab, intended for the final wearing course, installed
tween Structural Slab and Membrane—The insulation must be shortly after the membrane is installed could provide the
a structurally substantial material. It would appear mandatory necessary protection but could also be abused and damaged.
to superpose a stable, reinforced concrete slab over other less Methods by which the problem can be resolved are (1)
structurally adequate insulation types as a suitable substrate for temporary waterproofing requiring later removal, (2) tempo-
the membrane. If a concrete slab is provided over the insula- rary protection of the waterproofing (the quality and mainte-
tion, and especially if a second vapor retarder membrane is not nance of which could cause disputes among the various
provided on the structural deck, the insulation should be such interested trades), or (3) by a permanent concrete protection
as to (1) remain substantially unaffected by water absorption, slab. This slab could be placed soon after the membrane,
(2) be effectively resistant to freeze damage, and (3) be capable protection board, drainage course, and insulation, if required,
of sustaining imposed loads. This would appear to rule out have been installed. It would serve as protection for the
those insulations that contain vegetable fiber. Neither light- permanent waterproofing materials and insulation below, pro-
weight insulating concrete nor a protective concrete layer over vide a working platform for construction traffic and storage of
less structurally adequate insulation types are suitable sub- materials (within weight limits), and provide a substantial
strates for the membrane (see analysis in 6.2 and 6.3). substrate for the placement of the finish wearing course
12.3.5 Placement Between Membrane and Wearing materials near the completion of the project when they would
Course—With the membrane placed on the structural deck and be less vulnerable to damage. The protection slab should be
the insulation placed between it and the wearing course, a reinforced and be of sufficient thickness and strength to
good, stable substrate is provided for the membrane with a withstand the imposed loads. The slab would be the foundation
minimum of thermal cycling. Compared to other types, this substrate for the final wearing course materials and should be

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 C 981 – 05
not less than 76 mm (3 in.) in thickness (see Fig. 1). from 100 to 130 mm (from 4 to 5 in.) wide designed to
Prefabricated asphalt panels obtainable in a variety of widths, accommodate possibly 25 mm (1 in.) of movement may be
lengths, thicknesses, and compositions may be considered as undesirable from an appearance standpoint. Joint spacing is
an alternative protective cover for the membrane where light therefore usually limited to reduce the required width of the
limited construction traffic is expected. Temporary waterproof- joint, even though it may be technically feasible to use a wider
ing protection during construction must be evaluated with the spacing.
same importance as the final waterproofing system design 14.2.2 Special problems are encountered with expansion
concerning membrane (temporary flashings), construction traf- joints in an open-joint drainage system. As all the joints are
fic and its damage, drains, expansion joints, etc., as well as open, it would seem normal to have an open expansion joint.
methods of repair and re-replacement or removal of the The design certainly is simple but could create a hazard for
temporary protection system. small heels that could be caught in the open joints. Attempting
13.2 Joints—It is not necessary to seal the joints in the to provide a closed expansion joint in an open-joint drainage
protection slab but only to provide premolded resilient joint system also creates problems at the transverse joints when wet
fillers. The downward filtration of water through these joints sealants are used. Compression seals or sliding plates could
should be permitted so that the water can be drained away serve as solutions.
through the drainage course. Since cracks, joints, and move- 14.2.3 Sealed joints should be as durable and free of
ment in the protection slab affect the wearing course, joints in maintenance as possible. Premature deterioration of wet seal-
the two should be aligned and coordinated. A protection slab ant joints due to faulty design or installation can cause
module of about 6 by 6 m (20 by 20 ft) is reasonable to hazardous, unsightly conditions and result in high maintenance
minimize cracking and to keep the joint size minimal. Larger costs.
modules would require increased thickness and wider joint
14.2.4 The expansion joint in the wearing course, which of
widths, which would have to be continued through the wearing
necessity, is over the structural slab expansion joint below,
course.
does not necessarily have to be designed to accommodate the
14. Wearing Course same amount of movement as designed for in the structural
slab expansion joint. The important question to consider in
14.1 It is beyond the scope of this guide to cover in depth designing the expansion joint is whether the space below is to
the many technical considerations of the wearing course except be heated and air-conditioned, or opened to the outside, as in
those that are directly governed by the part of the system below the case of an underground, unheated parking space. If the
the wearing course. The major concerns are a stable support of space is to be heated below and insulated above, the greatest
sufficient strength, lateral thrust, adequate drainage to avoid movement in the joint would occur while the structure is
ponding of water on the surface, and proper treatment of joints unfinished, uninsulated, and not heated or air-conditioned.
in the wearing course. After the insulation is installed and the space below is heated,
14.2 Joint Treatment—The main concern in the wearing the movement will be decreased significantly. With a con-
course is the joints in which movement is anticipated. These trolled sequence of construction, a smaller and less costly joint
should be treated as expansion joints (see Fig. 11 for varia- can be used in the wearing course portion of the expansion
tions) with the following considerations: joint even though the slab joint below may show greater
14.2.1 The matter of appearance can influence the joint movement during earlier construction. The key to this is to
spacing and the type of joint design to be used. Widely spaced install the joint in the wearing course after the space below is
joints must be wider than those with a lesser spacing. Joints heated. There is always the risk, however, that the mechanical
system can fail or will be shut down and thereby cause greater
movement than designed for. In the case of an open or
unheated parking space below, the movement in the wearing-
course portion of the joint will continue after occupancy and its
width cannot be reduced. Intermediate joints in a protection
slab are normally spaced at closer intervals than those in the
latter, and their widths are related to the movement anticipated
for them as well as their joint treatment.
14.2.5 Various proprietary compression seals are available
that can be inserted into a formed joint under compression.
Most of these, however, are not flush at the top surface and
could fill up with sand or dirt.
14.2.6 Wet sealants are the materials most commonly used
in moving joints at the wearing surface level. Refer to Guide
C 1472 for calculating the appropriate width for joints. Refer to
Guide C 1299 when selecting sealant material. Refer to Guide
C 1193 for detailing the installation of sealant. Firm backing
FIG. 11 Schematic Expansion Joint Concepts at Wearing Surface material is preferred for horizontal joints subject to foot or
Level (see 14.2) wheeled traffic.

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 C 981 – 05
14.2.7 A drainage course may be desirable to facilitate water system, may be necessary to prevent water saturation of
drainage below the wearing course, particularly under mortar the soil. The thermal resistance of insulation must be sufficient
and concrete. Prefabricated drainage composites are available to prevent early budding of plant materials in areas subject to
for this purpose. Under vehicular traffic it is important to select winter dormancy.
a type that can bear the traffic loads. See Fig. 1.
16. Testing
15. Earth Fill and Planted Areas 16.1 Testing the membrane for leakage before additional
15.1 In areas of plaza decks where lawns or planting will materials are placed on it has the advantage of permitting
constitute the finish surface, the design procedure is similar to corrections to be made without having to remove any of the
that for the paved wearing surfaces, except that additional materials placed above it. Protection of the membrane is
criteria must be satisfied by the plaza system. Certain require- important because the placement of materials over it can
ments such as depth of soil, normal zone temperatures condu- sometimes damage an already tested membrane. One matter of
cive to the growth of the proposed plant materials and ground concern is the flow characteristics of the water as it gravitates
cover, soil temperature at roof systems, length of daylight and down to the membrane and then to the subsurface drainage
shade, and pH of soil, will regulate the design of the complete system. A slow restricted flow, by design or improper construc-
system. As most plants cannot tolerate a water saturated soil, a tion, can cause buildup of water pressure above the membrane
drainage course is essential. To prevent the intermixing of the before it is drained away. For testing methods, refer to Guide
planting soil and the drainage course, and thus the impedance D 5957.
of water movement, the placement of a durable permeable filter
above the drainage course is essential (see Fig. 12). Perforated 17. Keywords
drain pipes in the drainage course, connected with a storm 17.1 building decks; membrane; waterproofing

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 C 981 – 05

FIG. 12 Earth Fill and Planted Areas (see 15.1)

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