Practical Guide Date: April 2006

Flat roofs Written by:

Julie Garrigou Devichi
Checked by: John Rivers
Waterproofing concrete and steel decks

Stade de France, Paris West Middlesex Hospital, London Challenger, Saint-Quentin en Yvelines

Roof-top carpark Eco-roof Terrace

December 2005 BIIN CEA Practical guide - Flat roofs 1

Contents
A. Choosing a roofing system 4
B. Introduction: General terminology 5
1) Types of flat roofs for intended functions 6
2) Definition of acceptable fall 7
3) Geographical criteria 8
4) Composition of a flat roof
a) "Traditional" flat roof 9
b) Inverted roof 10
c) Traditional roof or inverted roof? 11
C. Design of each component
1) Loadbearing component 12
2) Vapour barrier
a) Purpose, installation 13
b) Points requiring special attention 14
3) Thermal insulation
a) General 16
b) Points requiring special attention 17
4) Bonding between insulation and waterproofing 20
5) The four kinds of flat roofing products 23
a) Asphalts 24
b) Sheets made with blown/modified bitumen 27
c) Polymer-based synthetic membranes 33
d) Liquid waterproofing systems 36
e) Points requiring special attention – types of roofing 39

December 2005 BIIN CEA Practical guide - Flat roofs 2

Contents (cont.)
6) Protection of waterproofing systems
a) Self-protection 44
b) Heavy protection 45
c) Roof-garden and eco-roof protection 48
d) Protection in accordance with intended function 52
7) Special works and features
a) Upstands 56
b) Rainwater discharge 57
c) Drains and gutters 58
d) Overflows 59
e) Roof penetrations 60
f) Expansion joints and curbs 61
8) Maintenance 63
D. Disorders 64
E. Examples of costs and application times 70
F. Standards and regulations
1) French standards and regulations 73
2) International standards and regulations 76
G. The industry world-wide
1) Manufacturers 77
2) Industry statistics 78
H. The architectural trades team of the Bâtiment International engineering division 79

December 2005 BIIN CEA Practical guide - Flat roofs 3

A – Choosing a roofing system
„ The choice of a type of a flat (or membrane) roofing system will depend on
the availability of products and local knowhow, as well as the overall cost
(including screed to falls, if necessary).

„ It is therefore vital to enquire into the local situation before anything else
and to then define the optimum roofing complex.

„ The points requiring special attention described in Chapter C should then

be checked for each system proposed:
… Points requiring special attention - insulation Page 17
… Points requiring special attention - waterproofing Page 39

NB: The term 'membrane roofing' is used in this guide in its more general sense, that of any
waterproof roof covering for use on a flat roof. The term therefore refers to membrane roofing
'proper' (high-performance bitumen-polymer sheeting types) and to built-up bitumen feltwork
or asphalt. [cf. The Penguin Dictionary of Building]

December 2005 BIIN CEA Practical guide - Flat roofs 4

B – Introduction - General terminology

„ 1) Types of flat roofs for intended functions

„ 2) Definition of acceptable fall
„ 3) Geographical criteria

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B - 1) Types of flat roofs for intended functions
„ The design of flat roofs is linked to the purposes for which they might be used. The density and
type of use of the roof will affect the choice of materials, their thickness, and the type of
protection to be applied. Flat roofs are classified as follows:
… Non-trafficable: flat roofs to be walked on only for routine maintenance of the flat roofing system and
related works such as skylights. There may be no fall, except in areas with mountain climates (where it
must be 1 to 5%).

… Plant: flat roofs walked on only for access to maintain rooftop plant (mechanical penthouses, roof-top air
conditioning units, etc.). There may be no fall, except in areas with mountain climates (where it must be
1 to 5%)

… Foot traffic: flat roofs designed for pedestrian use of any kind (circulation, sitting, standing, etc.).
Minimum fall must be 1.5%, except in the case of slabs on pedestals, when there may be no fall.

… Light vehicle traffic: flat roofs designed to allow circulation and parking of vehicles with a maximum
axle weight of less than 2 tonnes. The design rules for these roofs permit exceptional access for fire-
fighting vehicles and removal vans. Minimum fall of 2%.

… Heavy vehicle traffic: flat roofs designed for vehicles with an axle weight in excess of 2 tonnes,
including refuse trucks (up to 13.5 tonnes per axle). Minimum fall of 2%.

… Roof gardens: flat roofs covered with earth (at least 30 cm deep) and plants and shrubs (intensive
green roofs). Dead-flat fall is permitted; if the roof has walkways, the 1% fall required for water runoff can
be obtained with the walkway material.

… Eco-roofs: flat roofs covered with earth (up to 10 cm deep) and grass or ground-cover plants (extensive
green roofs). Falls can range from 0 to 25%.

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B - 2) Definition of acceptable fall
„ Principle
… The fall (or slope) of the roof is an essential factor in the classification of flat roofs. It
serves to drain rainwater to outlets and thus avoid problems that may arise out of pooling
of water.
… The fall is generally provided by the contractor for the building fabric, either in the form of
the loadbearing element itself or by laying a concrete screed ('screed to falls').
… Falls can also be created with insulation integrating falls. But not only is this solution
difficult to install, it is also costly: it uses more insulation, and requires extra costs for
design and manufacturing difficulties.

„ Terminology
… Dead-flat roof (≤ 1%)
… Nominally flat roof (falls from 1 to 5% inclusive)
… Inclined flat roof (falls from 5 to 18% inclusive)
… Pitched roof (falls greater than 18%)

„ This practical guide is confined to dead-flat, nominally flat, and inclined flat roofs. Pitched
roofs generally require special studies and use special waterproofing systems involving, in
particular, special fixings.

December 2005 BIIN CEA Practical guide - Flat roofs 7

B - 3) Geographical criteria
„ This guide is restricted to general cases outside mountain regions where wind and
snow conditions call for special rules to be applied.

„ The effect of climate must be appraised country by country. For example, it may be
necessary to increase the acceptable fall for flat roofs if there is likely to be heavy
rain, etc.

„ For each project, therefore, it is important to check the relevant standards and the
minimum fall requirements to be complied with.

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B – 4a) "Traditional" flat roof
„ Irrespective of the roofing system chosen, a flat roof consists of three
components overlying each other, each fulfilling a different function.

Loadbearing part:
1. Loadbearing element (concrete or steel deck)

Thermal insulation
2. Vapour barrier
3. Thermal insulation

Waterproofing
4. System bonding waterproofing and insulation
together
5. Waterproofing
6. Protection of waterproofing against impact and
UV radiation

December 2005 BIIN CEA Practical guide - Flat roofs 9

B – 4b) Inverted roof
„ Inverted roofs
… There are also flat roofs where the insulation is placed on top of the waterproofing layer.
These are known as "inverted roofs".
… This solution protects the waterproofing element from temperature variations, but
requires ballasting to prevent the insulation being swept away.
… On an inverted roof, the insulation must also remain unaffected by rainwater, for it is not
protected by the waterproofing. The main advantage of this system is that it makes the
building waterproof sooner and thus advances work on trades inside the building (e.g.
Brent Emergency Care and Diagnostic Centre – BECaD - in London).

Outside

1 ballast Inside
2 protective mat
3 insulation
4 waterproofing membrane
5 support

December 2005 BIIN CEA Practical guide - Flat roofs 10

B – 4c) Traditional roof or inverted roof?
„ Traditional (or 'warm') roof or inverted roof?
„ Advantages of the inverted roof
… The main advantage of the inverted roof is linked to construction scheduling: the
building is closed in sooner, making it possible to make earlier progress with internal
trades.
… No vapour barrier is required: the waterproofing acts as a vapour barrier.
… The waterproofing membrane is protected against thermal variations and ultra-violet
radiation.

„ Disadvantages of the inverted roof

… Heavy protection is vital.
… The insulation must be unaffected by damp (extruded polystyrene).
… Greater heat loss, so a thicker layer of insulant is required to achieve the same degree
of insulation.
… Upstands will be higher than with a warm roof (height from the roof slab/deck and not
just from the top of the insulant, as in the case of the warm roof).
… It is difficult to make insulated upstands with this roofing technique.
… Should not be used for buildings where the internal temperature is higher than 35°C or
on cold stores, to prevent condensation in the insulant.

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C - 1) Loadbearing component
„ This guide is restricted to two kinds of loadbearing component:

… Reinforced concrete – 60% of the market in France

„ Application (for France) is described in the DTU 20.12 code of practice

… Ribbed steel decking on framing – 40% of the market in France

„ Application (for France) is described in the DTU 43.3 code of practice
„ Steel decking is to be used only for untrafficked roofs or for access to plant.

NB: Timber flat roofs

„ Timber can be used as the loadbearing structure, but rarely. Its use is described (for
France) in the DTU 43.4 code of practice. Timber flat roofs are not dealt with in this
guide because they require special provisions.

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C – 2) Vapour barrier
„ Purpose: A vapour barrier prevents water vapour (or condensation) from rooms
beneath penetrating into the layer of insulation. It must be laid at a temperature
above 2°C.

„ Installation: The vapour barrier may be a flexible layer of bitumen with felt, glass-
fibre, or polyester reinforcement, in which case it is supplied in the form of 1m wide
strip in 20m rolls. Otherwise, the vapour barrier may be applied in situ in liquid
form, as hot-mopped (pour & roll) bitumen.
On a concrete roof slab, a cold tack coat is applied first to provide a sound
interface for the vapour barrier (see table, page 15).

„ Comments:
… The vapour barrier must be applied immediately before the insulation: it must under no
circumstances be used as temporary roofing and must not be considered to be a
waterproofing membrane.
… Inverted roofs do not need vapour barriers, since the waterproofing plays this role.
… In some cases no vapour barrier is required: e.g. hot countries where indoor
condensation does not occur.

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C – 2) Vapour barrier (cont.)
„ Points requiring special attention:
… The choice of a vapour-barrier system is linked to the support, the
climate (difference between indoors and outdoors), the humidity of the
room, to the type of insulation used, and of course to the waterproofing
system used.

… The instructions of the manufacturer of the waterproofing system

should therefore be referred to. Generally speaking, it can be said that
if the waterproofing system is a bituminous one, a bituminous vapour
barrier should be used, and if it is synthetic, a synthetic vapour barrier.

December 2005 BIIN CEA Practical guide - Flat roofs 14

C – 2) Vapour barrier (cont.)
„ Example: Composition and installation of a vapour barrier overlain by
modified bitumen
Vapour barrier
With hot-mopped bitumen Without hot-mopped bitumen
Heating and humidity of
premises Type Waterproofing visible or Beneath heavy Visible
beneath heavy protection waterproofing
protection
Standard case 2) Standard vapour Cold tack coat + hot- CTC + CTC +
barrier mopped bitumen (HMB) 25W50 EB 25W50 EB
+ 25W50 Elastom. Bit. fully torched on fully torched on
Premises with high humidity or Reinforced vapour Cold tack coat (CTC) + CTC + elasto-
heated floors providing only barrier hot-mopped bitumen + meric bitumen
part of the heating bitumen-backed 35 alum. fully
aluminium torched on
Premises with very high Reinforced vapour Cold tack coat + Cold tack coat
humidity or heated floors barrier on base- perforated bitumen felt1) + perforated
providing all of the heating sheet layer + hot-mopped bitumen base sheet +
+ bitumen-backed elastomeric
aluminium bitumen 35
alum. fully
torched on
1) At the perimeter and around penetrations the vapour barrier is bonded over a width of at Example of torched-on
least 0.50 mm without perforated bitumen felt or perforated base sheet.
aluminium-faced
2) "Standard case" refers to the roof slabs of premises with low to moderate humidity without
heat sources.
vapour barrier

December 2005 BIIN CEA Practical guide - Flat roofs 15

C – 3a) Thermal insulation - General
For full details on thermal insulation, refer to the Practical Guide of this series on
"Roof, Wall, and Floor Insulation". The very basic background is given below.
The insulants most commonly used with flat roofing systems are:
Cellular plastics foam insulants
… Expanded or extruded polystyrene (for inverted roofs, only extruded polystyrene can be
used for it is water-impermeable)
… Polyurethane
… Resol phenolic foams
„ Mineral insulants
… Mineral wool (rock wool only)
… Foam glass (looks like pumice stone)
„ Cellulose-based insulants
… Expanded/fibrous perlite
… Cork board

„ Irrespective of the insulant chosen, it must be remembered to check its

compatibility with the waterproofing system (this will be mentioned in technical
approval certificates and the manufacturer's recommendations).

„ Depending on the country and the conditions of the premises concerned, insulation
may be optional.
December 2005 BIIN CEA Practical guide - Flat roofs 16
 C – 3b) Thermal insulation – Points requiring special attention
Insulant Advantage Disadvantage Thermal
conductivity
(W/m°C)

Expanded polystyrene Poor fire resistance 0.04

Compressible: for non-trafficable
roofs only
Not suitable for inverted roofs

Extruded polystyrene Only insulant suitable for Poor fire resistance 0.029
inverted roofs
Hydrophilic
Incompressible: for roofs
subject to foot traffic
Resists freeze/thaw cycles
Polyurethane Incompressible: for roofs Poor fire resistance 0.026
subject to foot traffic Not suitable for inverted roofs
Hydrophilic

Rock wool Good fire resistance Compressible: for non-trafficable 0.038

roofs only
Not suitable for inverted roofs

December 2005 BIIN CEA Practical guide - Flat roofs 17

C – 3b) Thermal insulation – Points requiring special attention (cont.)
Insulant Advantage Disadvantage Thermal
conductivity
(W/m°C)
Foam glass Incompressible: for roofs subject Not suitable for inverted 0.042
to light-vehicle traffic roofs
Good impact resistance
Hydrophilic, can obviate need for
a vapour barrier
Good fire resistance
Does not rot
Fibrous perlite Incompressible: for roofs subject Not suitable for inverted 0.050
to light-vehicle traffic roofs
Good fire resistance
Ecological
Does not rot

Cork board Incompressible: for roofs subject Not suitable for inverted 0.042
to foot traffic roofs
Good impact resistance
Ecological
Does not rot

December 2005 BIIN CEA Practical guide - Flat roofs 18

C – 3b) Thermal insulation – Points requiring special attention (cont.)

„ Points requiring special attention relative to insulants:

… Installation: the choice of the installation method and combinations
with insulants are defined in the technical approval certificates for the
system concerned. It should be remembered that panels of single-ply
insulant should be placed in a broken-bond pattern. For multi-ply work,
the joints of successive plies must be offset from each other.

… Thermal conductivity factor λ (k value): the lower the thermal

conductivity factor, the more efficient the insulant, so the insulant can
be thinner.

… In all cases, the compatibility of the insulating material and the solvents
used in the glues and membranes must be checked by examining the
technical approval certificates for the products.

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C – 4) Bonding between insulation and waterproofing
„ There are three types of bonding:
… Loose laid
The separation layer is generally a sheet of glass-fibre fabric (100g/m²) placed between the
waterproofing system and its support (insulant, or slab/deck in the case of an inverted roof).
In addition, the first ply of the system has additional separation on the underside, e.g. Kraft crepe
paper.
The waterproofing system can only be laid loose if it is given heavy protection, with gravel for
example, otherwise it is likely to come off.

… Semi-loose or semi-bonded
This involves only partial bonding of the waterproofing to its support. It can be achieved with a layer of
perforated felt or by using dabs of hot bonding compound (hot bitumen) or cold bonding compound
(tack coat).
The advantage of this system is that it stands up well to deformation of the support.
It requires an insulant that is compatible with this kind of installation (see manufacturer's datasheet).
Semi-loose or semi-bonded laying can also be achieved with mechanical fixings (generally on ribbed
steel decking or aerated concrete).

… Fully bonded application

With fully bonded application, the waterproofing system is bonded to the entire surface, either using
the "pour and roll" technique (hot-mopped bitumen) or by torching-on in the case of insulation panels
suitable for use with torched-on waterproofing (see manufacturer's data sheet).
Fully bonded application is necessary in the case of a self-protective system. The insulation used
must be compatible with this kind of bonding.

December 2005 BIIN CEA Practical guide - Flat roofs 20

C – 4) Bonding system – Points requiring special attention

„ Points requiring special attention:

… In all cases the technical documentation for the system must be read.

… The choice of bonding system chiefly depends on the type of waterproofing

and protection. Loose laying, for example, can only be used under heavy
protection.

… The choice is also governed by local practice and features (high winds, for
example).

December 2005 BIIN CEA Practical guide - Flat roofs 21

C – 4) Bonding between insulation and waterproofing (cont.)

„ Loose laying
… Example of an EPDM membrane

„ Semi-loose laying
… Screw fixing through insulation

„ Bonded application
… Torching-on (flame) … Pour and roll (hot-mopped bitumen)

December 2005 BIIN CEA Practical guide - Flat roofs 22

C - 5) The four kinds of flat roofing products

„ a) Mastic asphalts and modified asphalts

„ b) Sheets made with blown bitumen or modified bitumen
„ c) Polymer-based synthetic membranes
„ d) Liquid waterproofing systems
„ e) Selection criteria

December 2005 BIIN CEA Practical guide - Flat roofs 23

C – 5.a1) Mastic asphalt
„ General
… The term 'mastic asphalt' covers all the products involving a combination of a 'mastic'
and a mineral skeleton.
… 'Mastic' is a mixture of bitumen and hydrocarbon-impregnated fines (passing a 0.08mm
sieve). It is characterized by its hardness.
… The skeleton is a mixture of sand and gravel.
… Mastic asphalt is mixed exclusively at batching plants.

„ Laying
… Mastic asphalts are laid hot in several layers. An asphalt waterproofing system must be
loose-laid (except for ramps).
… There are three kinds of traditional asphalt waterproofing systems:
„ 5+15 system: used for all kinds of flat roofs, it generally consists of 5mm of pure
asphalt and 15mm of a sand/asphalt mix. It may be left uncovered on non-trafficable
roofs if there is no significant temperature variation, but it is generally given hard
protection.
„ 5+20 system: This is similar to the 5+15 system but has a 20mm thick layer of
asphalt and gravel laid loose. It is used for flat roofs providing access to plant, that
can take light-vehicle and foot traffic, or can be protected by slabs on pedestals. It
can also be used for flat roofs taking heavy-vehicle traffic if given heavy protection.
„ Mastic asphalts are laid on supports with falls of no more than 3%.

December 2005 BIIN CEA Practical guide - Flat roofs 24

C – 5.a1) Mastic asphalt (cont.)
„ Ramp waterproofing: consists of two layers of a 25+25 "ramp-quality" gravel &
asphalt mix separated by glass-fibre mesh. It is not protected. It must be laid semi-
loose (at the least) or loose.
There are other types of mastic asphalt with technical approval, e.g.:
• 15+20 or 25 mm type for flat roofs subject to foot or light-vehicle traffic and roof gardens
(appropriate for multi-purpose roofs),
• 5+20 mm type for roof gardens,
• 8+20 to 35 mm type for special cases.
• 17 to 20 mm thick single-layer gravel & asphalt mixes, used exclusively on inverted roofs
• Composite waterproofing with a bituminous sheet membrane and a layer of gravel-
chipped asphalt.

Applying mastic
asphalt

December 2005 BIIN CEA Practical guide - Flat roofs 25

C – 5.a2) Modified asphalt
„ General
… Modified asphalt has only been used relatively recently
… The asphalt is modified by adding SBS elastomeric resins. It is used for waterproofing
flat concrete slab roofs with falls of no more than 3%.

„ Laying
… Modified asphalt is laid loose, as a 17 to 20 mm thick layer.
… It has good creep performance.
… A big advantage is that it can be applied at low temperatures.
… Example: "Novasphalte" for inverted flat roofs, by Smac Acieroid.

Modified asphalts should be covered by

technical approval certificates.

December 2005 BIIN CEA Practical guide - Flat roofs 26

C-5.b1) Sheets made with blown bitumen
„ General
… A blown-bitumen waterproofing system consists of a series of sheets of
reinforced-bitumen felt, etc. In the case of multi-ply work, the strips rolled out
are bonded together with bitumen (hot work) to form a continuous thick
membrane with a unit weight of about 10kg/m².

„ Composition of sheets
… Sheets consist of three main components:
„ One or more reinforcing materials to resist ageing and thermal and mechanical
effects,
„ A body of bituminous coating,
„ Surface treatment to resist solar radiation.

„ Use
… Blown-bitumen waterproofing membranes were for a long time the most
commonly used flat-roof waterproofing material in France. This trend has been
changed by increased use of two-ply compounds using modified bitumen (see
next section). Blown bitumen is practically no longer used.

December 2005 BIIN CEA Practical guide - Flat roofs 27

C-5.b2) Sheets made with modified bitumen
„ General
… Modified bitumen has added SBS copolymers (elastomers which make the
bitumen more elastic), APP copolymers (plastomers which make the bitumen
more plastic) or a mixture of elastomeric copolymers.
… These additions improve the physico-chemical properties of bitumen:
„ wider usable temperature range
„ flexible when cold and less brittle
„ stable at high temperatures and greater creep resistance
„ improved resistance to ageing factors such as sunlight.

„ Composition of sheets
… Reinforcement: the type (glassfibre fabric, glassfibre or synthetic scrim) and
unit weight of the reinforcement determine its strength generally, and
particularly punching resistance, as well as its thermal resistance.
… Surface treatment, either for self-protection (see section on protection), using
metal foil or bonded mineral particles, or for interfacing with the insulant,
depending on the application method adopted (compositions are defined in
manufacturers' technical data sheets).
… One or more layers of sheets (single ply or double ply).

December 2005 BIIN CEA Practical guide - Flat roofs 28

C-5.b2) Sheets made with modified bitumen (cont.)
„ Application
… Sheets may be loose laid. Consequently they can also be used on existing roofing
systems.
… They may also be applied semi-loose (to better withstand deformation of the support) or
fully bonded.

„ Characteristics
… Due to their composition, APP membranes resist ultraviolet radiation. On the other hand,
they are difficult to bond and apply in cold weather.
… SBS modified bitumen is suitable for cold climates since it can still be cold-pliable at
-40°C. On the other hand, it must be protected from UV radiation.
… Some bituminous membranes have enhanced fire resistance.
… Single-ply systems are less expensive than two-ply systems. However, two-ply systems
have a number of advantages over single-ply:
„ Better guarantee in the event of poor workmanship or other defect in application (since there are
two layers), and therefore less risk of leakage: the system is more reliable;
„ If the roof is to be trafficable for frequent access to equipment, two-ply is better because it has
better punching resistance;
„ Single-ply work should therefore be reserved for cases requiring minimum investment and when
the workmanship on overlapping of strips is likely to be good, i.e. when the roofing contractor is
experienced and its personnel is well trained.

December 2005 BIIN CEA Practical guide - Flat roofs 29

C-5.b2) Sheets made with modified bitumen (cont.)
„ Example of self-protected APP „ Two-ply work on concrete
single-ply work on steel decking

FALL 0 to 5%
FALL ≥3% GRAVEL

SECOND PLY
BENEATH PROTECTION
SINGLE PLY
HOT BITUMEN

FIRST PLY
HOT-BONDABLE INSULANT

SEPARATION LAYER

VAPOUR BARRIER INSULANT

IF REQUIRED
VAPOUR BARRIER

December 2005 BIIN CEA Practical guide - Flat roofs 30

C-5.b2) Sheets made with modified bitumen – FIT ranking (cont.)

„ The F.I.T. ranking is a performance-based classification of flat roofing

materials created by the CSTB (French building research institute) and the
Chambre Syndicale Nationale de l’Etanchéité (CSNE – French national
roofing association). It complements technical approvals. Blown bitumen
and liquid waterproofing systems are not addressed by the FIT ranking.

„ The letters FIT refer to:

… F: Fatigue strength (resistance to movement of support), from F1 to F5 – from
the least to the most resistant
… I: resistance to Indentation (static and dynamic punching), from I1 to I5 – from
the least to the most resistant
… T: Temperature (resistance to slippage resulting from high temperature), from
T1 to T4 – from the least to the most resistant

„ To help product specification, the FIT introductory document gives a table

indicating the minimum classification required for a waterproofing system
in accordance with trafficability criteria, the slope of the support, and the
protection of the system.

December 2005 BIIN CEA Practical guide - Flat roofs 31

C-5.b2) Sheets made with modified bitumen – FIT ranking (cont.)
USE OF ROOF AND TYPE OF PROTECTION
PLANT
SLOPE self- Loose self- Slabs foot traffic vehicles foot traffic garden
protecting hard prot.
(%) a b protecting b hard prot. slabs

THERMAL to
INSULATION

CONCRETE to

CONCRETE AND
INVERTED
INSULATION to
CELLULAR to
CONCRETE
WOOD AND WOOD- to
BASED PANELS

OLD ROOFING to

a : I taken as 3 for single ply

b : I taken as 4 for single ply
c : I taken as 3 for mineral wool on concrete
d : I taken as 3 for mineral wool with Rth > 2 m².°C/W
e : I taken as 4 for mineral wool on concrete, cellular concrete, or polystyrene
f : T taken as 3 if Rth > 2 m².°C/W

For asphalt systems, the FIT classification is replaced by a fitness-for-use table.

December 2005 BIIN CEA Practical guide - Flat roofs 32

C – 5.c) Polymer-based synthetic membranes
„ General
… Polymer-based synthetic membranes are flexible manufactured sheets. They are
covered by technical approval certificates. They are single-ply systems.

„ Composition of sheets
… The sheets are made with synthetic 'high-polymer' resins. Two kinds of membranes in
particular are used:
„ Elastomeric membranes: EPDM (synthetic rubber made to dimension, in a single
seamless piece, or in rolls fixed mechanically with special fixings which do not pierce
the waterproofing).
„ Thermoplastic membranes – PVC, CPE or PIB

… They may or may not be reinforced for improvement of performance or to provide

interfacing if fully bonded. They are generally 1 to 3 mm thick.

December 2005 BIIN CEA Practical guide - Flat roofs 33

C – 5.c) Polymer-based synthetic membranes (cont.)
„ Application
… Laid loose with heavy protection
… Semi-loose (partial bonding or mechanical fixing)
… Fully bonded
There are several ways of assembling strips in the workshop or on site, in accordance
with technical approval certificates.
In all cases, applicators must be trained and approved by the manufacturer.
Polymer-based synthetic membranes are chiefly used for renovating large flat roofs, for the
mechanical fixing system allows them to move with the support.

„ Characteristics:
… Polymer-based synthetic membranes are generally strong, stand up well to the cold,
heat, chemicals, and weather.
… EPDM (EPT) membranes can be applied over existing bituminous roofing.
… PVC membranes are more long-lasting since they have polyester or glassfibre
reinforcement. They resist ultraviolet radiation better than EPDM.
… CPE membranes (unvulcanized chlorinated polyethylene polymer) are similar to PVC but
contain no plasticizer. They are therefore slightly less flexible.
… PIB membranes (unvulcanized polyisobutylene polymer) are backed with a polyester felt
reinforcement that absorbs any roughness in the support. These membranes stand up
well to weather and punching (perforation) but do not have good fire resistance.

December 2005 BIIN CEA Practical guide - Flat roofs 34

 C – 5.c) Polymer-based synthetic membranes (cont.)

„ Example: self-protecting „ Example: self-protected PVC

membrane, mechanically fixed membrane (Barking Schools,
with special screws, for non- London)
trafficable flat roofs

FALL ≥1%

MECHANICALLY FIXED
PVC MEMBRANE

BASE SHEET
IF REQUIRED

THERMAL
INSULATION

VAPOUR BARRIER

December 2005 BIIN CEA Practical guide - Flat roofs 35

C – 5.d) Liquid waterproofing systems
„ General
… Liquid waterproofing systems: waterproof roofing systems using synthetic thermoplastic or
thermosetting resins.
… They are generally applied in several layers (2 or 3).
They are applied hot or cold, depending on the composition of the compound. As it dries, the compound
bonds to its support.
… Liquid waterproofing systems stand up quite well to cracking of their support.

„ Composition of liquid waterproofing systems

… The main component (binder) of these compounds is a polymeric resin (polyurethane, acrylic,
polyester).
… They are generally used in conjunction with reinforcement (polyester fabric).
… They form a seamless membrane in situ.

„ Application
… Caution: some liquid waterproofing systems are for use exclusively on supports with hydraulic binders
(see data sheets).
„ Monolithic reinforced-concrete slab or precast reinforced or prestressed concrete units.
„ Screed to falls bonded to loadbearing element.
„ Reinforced or unreinforced screeds or slabs bonded to the support.
„ The minimum fall required is 1%, except in certain cases, for some recent products (see supplier's documentation).
… In all cases, liquid waterproofing systems are fully bonded to their supports. The most general case is:
„ primer coat,
„ first coat of resin forming the first layer of the system, with reinforcement (such as polyester fabric)
„ second coat of resin forming second layer.

December 2005 BIIN CEA Practical guide - Flat roofs 36

C – 5.d) Liquid waterproofing systems (cont.)
„ Characteristics
… After polymerization, liquid waterproofing systems bond to the support
and stand up well to cracking.
… They have the advantage of adapting completely to the shape of the
works.
… There is no problem with making seams between strips.
… Some are applied cold, requiring neither heat nor flame.
… Some resin systems are non-skid and come in different finishes
(uniform colour, marbled, chipped, or gritted); they can be walked or
driven on as-is, without additional protection, or can be tiled (bonded
tiling).
… However, liquid waterproofing systems require highly qualified
applicators.
… They mostly require favourable weather conditions for application.
… They must be protected from impact and traffic while setting.

December 2005 BIIN CEA Practical guide - Flat roofs 37

C – 5.d) Liquid waterproofing systems (cont.)
„ Example: SEL Decothane, by Liquid Plastics Ltd., used for the BECaD
Hospital project in the United Kingdom (inverted roof).
„ Unlike "old" liquid waterproofing systems, this particular product can be applied to damp roofs
and requires no screed to falls.

Waterproofing layer
Gravel
Filter layer
Special inverted-roof insulation
Waterproofing layer
Reinforcing fabric
Waterproofing layer
Concrete slab

December 2005 BIIN CEA Practical guide - Flat roofs 38

 C – 5.e) Points requiring special attention – types of roofing
Water- Advantages Disadvantages Points requiring Associated
proofing special attention protection
(see C.6)
Asphalt -Toughness - Changes in appearance over time - On roofs with falls of 3% - Protection obligatory
- Durability, taken to be and becomes whitish grey or more, on very hot if on insulation
> 25 years - Poor punching resistance days, it tends to run (due support in regions
- Good resistance to
to the high temperature) with high temperature
imposed loads variations and on
trafficable roofs
- Modified asphalt is
very suitable for - Loose, hard, or
multipurpose roofs gravel-chipped
asphalt protection

Blown - Low elasticity compared to Do not use. Has practically - Protection of sheets
polymer-modified bitumens disappeared from the obligatory. Applied
bitumen Sensitive to large temperature market either in the
multi-ply variations workshop (self-
- Durability (10 years): the shortest protecting system) or
lifetime heavy protection
- Poor punching resistance

December 2005 BIIN CEA Practical guide - Flat roofs 39

 C – 5.e) Points requiring special attention – types of roofing (cont.)
Water-proofing Advantages Disadvantages Points requiring Associated
special attention protection
(see C.6)
Modified- - Minimum - The slightest leak will have - Careful control of - Protection obligatory.
investment serious consequences work and solid Either shop-applied (self-
bitumen single references of protected system coated
- Low punching resistance
ply subcontractor with pellets, chips, metal,
prefabricated metal
sheets of aluminium,
stainless steel, or copper),
or heavy protection (hard
or loose)

Polymer- - Durability, taken to - Low punching resistance - Application requires - Protection obligatory.
be > 25 years great care Either shop-applied (self-
modified protected system coated
- Good elasticity - Until protection has
bitumen two- - Good bonding to been applied traffic with pellets, chips, metal,
ply support or tools placed on prefabricated metal
the roof can easily sheets of aluminium,
- Economical stainless steel, or copper),
perforate the
- Application quite waterproofing or heavy protection (hard
simple or loose)

December 2005 BIIN CEA Practical guide - Flat roofs 40

 C – 5.e) Points requiring special attention – types of roofing (cont.)

Water- Advantages Disadvantages Points requiring special Associated

proofing attention protection
(see C.6)
Polymer - Durability, taken to be > 25 - Specialist labour: - Beware of incompatibilities in - Polymer
years welding of membranes the case of rehabilitation of membranes can
membranes requires special existing roofing: there must be either be left
- Many special prefabricated
accessories (corner pieces, certification in the a chemical separation between unprotected (most
overflows, cable technique the PVC and bitumen, asphalt, common case), or
penetrations) - Slippery surface in rain or expanded polystyrene be protected by
- Quick to apply - Check that the contractor loose heavy
employs trained personnel protection or slabs
- Aesthetics: smooth, many on pedestals
colours available qualified for welding of
membranes (refer to technical
- Eco-friendly: the main four approval
manufacturers are - Some membranes can only be
applied in fair weather certificates or
committed to recycling their specifications)
products at the end of their
lifetime

December 2005 BIIN CEA Practical guide - Flat roofs 41

 C – 5.e) Points requiring special attention – types of roofing (cont.)

Water- Advantages Disadvantages Points requiring Associated

proofing special attention protection
(see C.6)

Liquid - Seamless waterproofing (no - Often the most expensive - Practical for upstands, - Liquid
waterproofing joints) waterproofing system to small areas, where hot- membranes may
Applied without flame or hot supply work (flames) is prohibited be left
systems -
air - Some systems cannot be and application of rolls is unprotected, with
- Can be used for complex applied over insulation: difficult different
shapes (curves, undulations) restricted to uninsulated - Check that the contractor decorative
and where access is difficult roofs, balconies, etc. (see employs trained staff finishes, or may
(gutters) technical approval qualified for application of have loose heavy
certificates) or inverted roofs. resins protection or
- Range of decorative finishes slabs on
possible for some products. - Major constraints on - Check weather conditions
application for some for application against the pedestals (refer
Transparent resins can be to the technical
used to waterproof systems: good-bonding data sheet
support (clean and dry), approval
transparent structures certificates or the
- Quick to apply temperature, no humidity
specifications for
- Requires specialist workforce each product)

December 2005 BIIN CEA Practical guide - Flat roofs 42

C – 5.e) Points requiring special attention – types of roofing (cont.)

„ SUMMARY:
… The main selection criterion are availability of products and local knowhow,
plus the overall price (ratio between knowhow / materials cost / labour cost).

… Check whether or not a screed to falls is required, depending on the intended

purpose of the roof and the waterproofing system adopted (refer to the
technical data sheet to check whether or not the waterproofing resists ponding
of water).

… New liquid waterproofing systems marketed recently do not require screeds to

falls and can be applied even in wet weather. They are of great interest in
countries where labour is expensive, for application is fast.

… Materials are constantly evolving. Some were originally developed for civil
engineering applications (Integritank liquid system by de Stirling Lloyd, for
example).

December 2005 BIIN CEA Practical guide - Flat roofs 43

C – 6.a) Protection of waterproofing systems
„ Protection is the visible part of the roofing system; its role is to protect the
waterproofing against the natural effects of ultraviolet radiation, temperature
variations, wind, and the mechanical effects of foot or vehicle traffic, loads, and
impact.

„ It is vital that it be resistant: if the protection deteriorates, the waterproofing might

become damaged and cause leaks.

„ The type of protection chosen will depend very much on the purpose of the flat
roof.

„ Self-protection: Self-protected systems are intended only for non-trafficable flat

roofs and upstands.
… The protection is applied to the face of the waterproofing system in the manufacturer's
workshop. The self-protection layer is bonded to the waterproofing and is only a few
millimetres thick. It can be metal (embossed copper, aluminium, or stainless steel) or
mineral (slate chips or fine gravel of different colours).

… It is particularly suitable in the case of steel roof framing, for it reduces the weight carried
and thus avoids having to increase the size of loadbearing elements.
December 2005 BIIN CEA Practical guide - Flat roofs 44
 C – 6.b) Protection of waterproofing systems: heavy protection
„ Added protection or heavy protection. Heavy protection is applied immediately
after application of the waterproofing system to prevent damage.
„ There are two types: 'loose' and 'hard' heavy protection

„ Loose protection (ballast)

… Loose protection is used only on non-trafficable roofs since traffic on the gravel would be
likely to puncture the waterproofing. It consists of a 4 to 6 cm thick bed of river gravel.
… Crusher gravel can also be used, but is more likely to damage membranes. Crusher gravel
can only be placed on thick membranes such as APP or SBS modified bitumen systems
reinforced with polyester fabric, in which case it is recommended in any case that an
intermediate protective layer of polyester or polypropylene matting be placed beneath the
ballast.
… For paths leading to plant, slabs or steel grating walkways should be laid.
… Loose protection should be avoided in very windy locations for gusts of wind could blow
gravel off the roof (risk of injury, broken glass, etc.). It is even prohibited for certain
buildings: at airports, for instance.
… If the building is more than 28 m high or is in a windy location, the gravel around the edge
of the roof or around skylights, etc. should be bonded at the surface or weighed down with
concrete slabs over a width of 2 metres.
… The gravel used must be 'clean' in order to prevent plant growth, and it must be carefully
maintained.
… The maximum fall for application of gravel is 5%.

December 2005 BIIN CEA Practical guide - Flat roofs 45

 C – 6.b) Protection of waterproofing systems: heavy protection (cont.)
„ Hard protection
„ Hard protection is obligatory for all trafficable flat roofs (except for asphalts and some
liquid waterproofing systems which also fulfil a protective role). Hard protection
consists chiefly of:
… Reinforced concrete topping slab laid on a 3 cm layer of gravel
… Pavers set in sand
… 50 cm square slabs placed on height-adjustable pedestals
… Tiles set in mortar
… Site-cast mortar or concrete support for tiled walkways.

December 2005 BIIN CEA Practical guide - Flat roofs 46

C – 6b) Protection of waterproofing systems (cont.)
„ Self-protected
waterproofing
… Slate chips

… Metal foil

„ Gravel protection

„ Hard protection
(e.g. slabs on pedestals)

December 2005 BIIN CEA Practical guide - Flat roofs 47

C – 6c) Protection of waterproofing systems: gardens and eco-roofs

„ Roof gardens and eco-roofs

… Roof gardens
„ Roof gardens generally receive foot traffic and look like traditional gardens.
„ They can be built only on concrete roof slabs. The depth of soil can vary from 0.30
to 1.00 m.

December 2005 BIIN CEA Practical guide - Flat roofs 48

C – 6c) Protection of waterproofing systems: gardens and eco-roofs (cont.)

… Eco-roofs
„ Eco-roofs are not trafficable. Access is restricted to the purposes of maintenance of
the waterproofing and plants.
„ Plants are chosen to require less maintenance and watering than roof gardens.
They are hardy ground-cover plants (25 cm high at most) with low nutritional
requirements that reproduce and spread well. Mixing several carefully selected
varieties achieves a multicoloured effect that changes with the seasons.
„ The soil depth is small (3 to 20 cm) and therefore implies low imposed loads on the
structure (115 to 135 kg/m²). Eco-roofs can therefore be built on concrete, steel or
wooden loadbearing members.

December 2005 BIIN CEA Practical guide - Flat roofs 49

C – 6c) Protection of waterproofing systems: gardens and eco-roofs (cont.)

… The special features of roof gardens and eco-roofs are as follows

(see illustrations overleaf).
„ A waterproofing system treated with a root-repellent; the product's data sheet should
be consulted.
„ A drain layer conveying water to outlets and enabling roots to breathe; it consists of
expanded clay aggregate, pozzolane, pebbles, gravel, or sheets of ribbed cellular
polystyrene; it is between 6 and 10 cm thick.
„ A filter layer holding back fines of the topsoil to prevent them clogging the drainage
layer; it must be watertight and rotproof, and resist tearing and punching
(perforation); it usually consists of layers of rockwool or non-woven synthetics.
„ A layer of soil, between 3 and 20 cm deep for eco-roofs and 30 cm and 1 m deep for
roof gardens.
„ There should be a sterile zone or edging about 40 cm wide around the perimeter of
the roof to facilitate inspection of upstands, rainwater drainage, and the height of
upstands.
„ This sterile zone must be separated from the eco-roof area by perforated metal
strips or concrete or brick kerbs holding back the earth but allowing water to drain
out.

December 2005 BIIN CEA Practical guide - Flat roofs 50

C – 6c) Protection of waterproofing systems: gardens and eco-roofs (cont.)

„ Roof garden „ Eco-roof

FALL 0 to 5% FALL 0 to 20%

SOIL (>30 cm) GROWN MEDIA

FILTER LAYER FILTER LAYER

DRAINAGE LAYER
DRAINAGE LAYER
SECOND LAYER

SECOND LAYER FIRST LAYER

SEPARATION
FIRST LAYER LAYER
(fall ≤ 5%
SEPARATION
LAYER

INSULATION
INSULATION
VAPOUR BARRIER
VAPOUR BARRIER
COLD TACK COAT
COLD TACK COAT

December 2005 BIIN CEA Practical guide - Flat roofs 51

C – 6.d) Protection in accordance with intended function
„ Protection of non-trafficable flat roofs
… Self-protection of waterproofing system
The appropriate waterproofing systems are:
„ 5+15 asphalt: exclusively on concrete roof slab without insulation in climates without
great temperature range; otherwise 5+20 asphalt or modified asphalt.
„ Self-protected single-ply or two-ply bituminous systems with surface treatment with
slate chips or metal foil. The insulant to be used will be chosen in accordance with
the technical data for the product.
„ Synthetic membranes with UV treatment. Check the technical data to ensure the
insulation is compatible.
„ UV-resistant liquid waterproofing systems. Check the technical data to ensure the
insulation is compatible (generally polyurethane or special insulation with compatible
surface treatment).

… Heavy protection (gravel)

All waterproofing systems are generally compatible with heavy protection.
Limitations on insulation concern the compatibility of the waterproofing system
(refer to technical datasheets for waterproofing).

December 2005 BIIN CEA Practical guide - Flat roofs 52

C – 6.d) Protection in accordance with intended function (cont.)
„ Protection of flat roofs for building services
The case of roofs for building services (plant) is very similar to that of non-
trafficable roofs. The following special precautions must be taken to strengthen
walkways.
… Self-protection of waterproofing system
„ Asphalt: Not compatible with 5+15 asphalt systems. Exclusively modified asphalts
(refer to manufacturers' technical documentation, e.g. Smac Acieroid).
„ Bituminous single-ply or two-ply systems: special reinforced mineral self-protection
for walkways.
„ Synthetic membranes: refer to technical datasheet to check compatibility.
„ Liquid waterproofing systems: a fibre-reinforced system is generally used to improve
resistance to foot traffic. Check the technical datasheet of the product.

… Heavy protection
„ Slab protection: precast concrete or natural stone slabs laid on a separation layer
(bed of aggregate, loose protection, non-woven fabric, or polystyrene), except in the
case of asphalt waterproofing where the slabs may be laid directly on the asphalt.
„ Cast-in-place concrete topping slab on separation layer.

December 2005 BIIN CEA Practical guide - Flat roofs 53

C – 6.d) Protection in accordance with intended function (cont.)
„ Protection of flat roofs accessible to pedestrians
… Self-protection
„ Asphalt: 15+25 asphalt serves as both waterproofing and protection for flat roofs
open to pedestrian traffic, and is laid directly on a concrete roof slab.

… Heavy protection
„ Cast-in-place topping slabs on separation layer.
„ Tiles in mortar.
„ Slabs on pedestals.
„ Precast concrete or natural stone slabs on separation layer.
„ Interlocking concrete pavers.
„ All kinds of roof waterproofing include systems that can take heavy protection.
Generally speaking, bituminous membranes or liquid waterproofing systems are the
most suitable. Check the product technical datasheet in all cases.

December 2005 BIIN CEA Practical guide - Flat roofs 54

C – 6.d) Protection in accordance with intended function (cont.)
„ Protection of flat roofs taking light-vehicle traffic
… Self-protection
„ 15+25 asphalt waterproofing
… Heavy protection
„ Reinforced concrete topping slabs on separating layer
… Refer to the product technical datasheet to check that the waterproofing system is compatible with light-
vehicle traffic.
„ The only insulant currently compatible with vehicle traffic is foam glass.

„ Protection of flat roofs taking heavy-vehicle traffic

… Heavy protection
„ Cast-in-place reinforced concrete topping slabs on separating layer

„ Protection of ramps
… Self-protection
„ 25+25 asphalt on concrete support
… Heavy protection
„ Cast-in-place reinforced concrete topping slabs on separating layer

„ Protection of roof gardens

… Refer to Section C – 6c) Protection of roof gardens and eco-roofs

December 2005 BIIN CEA Practical guide - Flat roofs 55

 C – 7) Special works and features
„ a) Upstands
… Definition: An upstand is the waterproofing applied to works standing proud of (above) the
roof surface.
… Upstands are waterproofed separately from the waterproofing of horizontal surfaces and are
connected to the main part by overlapping and welding or bonding.

Non-trafficable flat roof Trafficable flat roof

Self-protected upstand, ≤ 1 m high Upstand with hard protection

Drip at top of
upstand (weak
Drip at top of point No. 1)
upstand (weak Reinforced cement
point No. 1) render
Bonded self-protected
upstand Waterproofing
2nd layer
Angle reinforcement, 1st layer
0.25 m total width Upstand angle
Upstand angle (weak point No. 2)
(weak point No. 2) Rotproof flexible
seal
(0.02 m min.)
Hard protection
Waterproofing of
standard zones Waterproofing of
standard zones
Thermal insulation
Monolithic Vapour barrier Monolithic Thermal insulation
support support
Concrete load- Vapour barrier
(concrete or (concrete or
bearing element Concrete load-
metal curb) metal curb)
bearing element
Horiz. part of angle Horiz. part of 1st layer
reinforcement upstand waterproofing
Horiz. part of Horiz. part of 2nd layer
upstand upstand waterproofing
waterproofing

December 2005 BIIN CEA Practical guide - Flat roofs 56

C – 7) Special works and features (cont.)
„ b) Rainwater discharge
… Rainwater outlets
„ The waterproofing system is connected to the drainage system by rainwater outlets, the base
plate of which is inserted into the waterproofing system.
„ The layout of rainwater outlets should be such that no water will flow more than 30 m on the
waterproofing. Preferably, there should be one outlet for every 100 square metres.
„ All outlets must be fitted with a system to hold back debris that might clog rainwater pipes (e.g.
balloon grating).
„ The diameter of the rainwater pipe will be chosen in accordance with the discharge rate and the
equivalent horizontal surface area drained by the outlet (in France, refer to the tables of code of
practice DTU 43.1; otherwise, refer to the design rules of each country, in accordance with
rainfall statistics).

Key:
1 Gravel barrier
2 Waterproofing
3 Gravel
4 Self-protected waterproofing
5 Balloon grating

December 2005 BIIN CEA Practical guide - Flat roofs 57

C – 7) Special works and features (cont.)
„ c) Drains and gutters
… For the purposes of this guide, a box gutter is defined as a channel for collecting rainfall,
generally rectangular in section, that is installed on a non-trafficable flat roof. It may be
placed between two slopes or at the bottom of a single slope. All falls may be used,
including dead flat.

… For the purposes of this guide, a drainage channel is defined as a channel for collecting
rainwater, generally rectangular in section, that is installed on a trafficable roof and
covered with a removable protective grille (separate units) for easy maintenance and to
ensure safe circulation. Falls of up to 0.5% may be used.
Box gutter Covered drainage channel
width

December 2005 BIIN CEA Practical guide - Flat roofs 58

C – 7) Special works and features (cont.)
„ d) Overflows
Overflows are openings in the horizontal roofing or in parapet walls that
will discharge rainwater in the event of accidental undercapacity of the
normal rainwater discharge system. Horizontal overflows should preferably
be rectangular in section, with the wide side horizontal. The minimum
sectional area is 28 cm².

Key:
1 Overflow
2 Waterproofing system
3 Insulation
4 Vapour barrier

December 2005 BIIN CEA Practical guide - Flat roofs 59

C – 7) Special works and features (cont.)
„ e) Roof penetrations
… Pipes, TV aerial ducts, etc. routed through the roof and connected to the waterproofing
system by means of a baseplate and a sleeve joined together by a watertight weld.
… Pipes may be embedded in a block of concrete. A standard upstand is then applied
around and on top of the block.
… Safety railing posts can be connected in the same way.

Non-metallic ventilation pipe (PVC) with block of concrete for connection to waterproofing system -
Example

Key:
1 Block of concrete
2 Mastic
3 Collar
4 Collar flashing
5 Steel pipe sleeve
6 Top of protection
7 Non-metallic pipe
8 Loadbearing structure

December 2005 BIIN CEA Practical guide - Flat roofs 60

C – 7) Special works and features (cont.)
„ f) Expansion joints
… In general, expansion joints must be located at projecting curbs. Flat joints are
acceptable only for certain types of trafficable roofs when curbs cannot be built
because of the purpose for which the roof is used.

… Joint at double curb

If the waterproofing at a double-curb expansion joint is to be continuous, the
part waterproofing the joint itself consists of a strip of material regulated by a
technical approval certificate folded to form a 'bellows piece" (see diagram
overleaf) whose edges are secured to the curbs on each side of the joint.
The hollow part of the bellows piece must be filled with a suitable sealing
material.
To prevent penetration by foreign objects, the joint must be capped with a
sheet of self-protecting waterproofing material.
A coping (hard stone, concrete, or metal flashing) may be fitted over the entire
system.
Upstands must be applied to the sides of the curbs and may be carried over
the top.

December 2005 BIIN CEA Practical guide - Flat roofs 61

C – 7) Special works and features (cont.)
„ Upstand on skylight curb or „ Expansion joint on concrete
similar double curb
STEEL CURB WITH COLD TACK COAT
PREVAILING WINDS
FLEXIBLE BEAD
TOP LAYER

UNDERLAYER BELLOWS
ANGLE REINFORCEMENT

SECOND LAYER, STANDARD SECTION

UPSTAND
FIRST LAYER, STANDARD SECTION TOP LAYER

THERMAL INSULATION

NB: In the case of single-ply waterproofing, the angle

reinforcement is bonded either to the insulation board (bonded
system) or to the waterproofing sheet (loose system)

December 2005 BIIN CEA Practical guide - Flat roofs 62

C – 8) Maintenance
„ A flat roof must be checked and maintained by a specialist contractor at
least once a year.

„ The inspection will concern the performance of the upstands, joint covers,
ventilation ducts, etc. …

„ … and above all the cleanliness of the roof, for plants are the sworn
enemies of flat-roof waterproofing since their roots can perforate the
membrane.

December 2005 BIIN CEA Practical guide - Flat roofs 63

D) Disorders
„ 1) Design and construction problems for flat roofs with heavy protection
… Disorders in flat roofs with heavy protection involve leakage to the underside of
the loadbearing structure despite protection by a topping of concrete or mortar,
with or without surface finishing (tiling, for instance).

… Symptoms: as a result of variations in humidity levels, the topping expands and

contracts. The waterproofing separates from the support and tears.

… Causes and prevention:

„ Too large a screed: when the screed is laid, it must be remembered to create
movement joints dividing it into areas of less than 10 m² with joints less than 4 m
apart in both directions. They should be 1 to 2 cm wide and filled with a flexible
sealant. They will allow the mortar to expand freely.
„ The screed is bonded to the waterproofing: this should not occur; a separation layer
(sand, polyethylene slip membrane, bitumen felt) should be placed between the
waterproofing and the screed.

December 2005 BIIN CEA Practical guide - Flat roofs 64

D) Disorders (cont.)
„ 2) Upstand design and construction problems
… Most disorders affecting the waterproofing of flat roofs concern special
points of the roofing. Upstands are more particularly affected by either
poor workmanship or a defect in their top protection.

… Symptom No. 1: Upstand debonding

„ Causes and prevention:
… The upstand must be bonded, at the right temperature, to a clean, dry support.
If it is too hot, the bitumen loses its plasticity; not hot enough, and it does not
melt enough and the upstand does not stick to the support.
… The support must be dry when the upstand is applied, and it must stay dry. If
the protection at the top of the upstand is faulty (dislocated fillet, no drips),
runoff will penetrate between the concrete support and waterproofing by
capillary action, and the waterproofing will eventually become debonded.
… If the upstand is not high enough, splashes from falling water can wet the
support.

December 2005 BIIN CEA Practical guide - Flat roofs 65

D) Disorders (cont.)

Upstands repaired and once again debonded because of

insufficient top protection (cracked fillet, drip not wide enough).

December 2005 BIIN CEA Practical guide - Flat roofs 66

D) Disorders (cont.)
… Symptom No. 2: Torn upstand
„ Causes and prevention:
… Large precast parapet wall units can be sensitive to thermal differentials. If they
crack, they damage the upstands applied to them.
… If there is no peripheral movement joint, when the hard protection on the roof
expands, it can cut through the bottom of the upstand, close to the angle.
„ Solutions:
… Upstands must be bonded to a monolithic support and must not cross
expansion or movement joints.
… The top of upstands must be protected by an effective system intercepting
runoff and having a drip to cast off water.
… The materials used must be of good quality and be applied (bonded) with care.
Reinforced materials will better withstand tensile forces, making application
easier.
… At the time of acceptance of the works, it is vital to check that upstands are
properly bonded, are the correct height, and are properly protected at the top.

December 2005 BIIN CEA Practical guide - Flat roofs 67

D) Disorders (cont.)
„ 3) Problems during application.

Care should be taken not to damage the waterproofing as

a result of:
… Allowing traffic on the roof too soon

… Placing (or dropping) materials, scaffolding, or tools on the

roof during the works

Machine
foot
… Placing permanent point loads on the roof without protection
or without checking that the insulation can support the
weight (in general the solution is to increase the contact area
between the baseplate and the roof structure).

… Hailstones

December 2005 BIIN CEA Practical guide - Flat roofs 68

D) Disorders (cont.)
„ 4) Other disorders
There are many other disorders that can affect
roofing membranes. They include:
… Tears, generally due to excessive tensile stress in
the plane of the membrane. This is generally due to
contraction of the material, instability of the support,
or poor workmanship on movement joints.

… Blisters, due to trapped pockets of damp air or

water vapour between different layers of multi-ply
roofing, or between the insulation and the
waterproofing. Blisters form weak points in the
membrane.

… Folds, generally due to poor fixing of the membrane

or too high an expansion factor for the material of
which the membrane is made.

December 2005 BIIN CEA Practical guide - Flat roofs 69

E) Examples of costs and application times
„ The factors affecting the cost of a waterproofing system are chiefly:

… Labour costs
… Local knowhow and availability of roofing materials
… Whether or not screeds to falls are required
… The quantity of upstands (it is longer and more complicated to apply an
upstand in a two-ply system than in a liquid polyurethane waterproofing
system).

December 2005 BIIN CEA Practical guide - Flat roofs 70

E) Examples of costs and application times (cont.)
Examples of average costs EXCLUDING screed to falls and accessories.
„ France
… Self-protected two-ply system with 80-mm-thick polyurethane insulation €35 to 40 / m²
… Self-protected two-ply system (upstand) without insulation €8 to 9 / m
… Two-ply system with gravel protection and 80-mm-thick polyurethane insulation €37 to 42 / m²
(standard surface)
… Inverted-roof asphalt waterproofing with 50-mm-thick extruded polystyrene €38 to 45 / m²
insulation and 60 mm of gravel (standard surface)

„ Turkmenistan
… Two-ply waterproofing system (standard surface) with 60-mm-thick US$17 to 25 / m²
polyurethane insulation and 5 cm topping
… Self-protected two-ply waterproofing system (upstand) without insulation US$6 to 10 / m

„ United Kingdom
… Inverted-roof liquid waterproofing system (standard surface) with 120-mm-thick £38 to 45 / m²
extruded polystyrene insulation and 5 cm of gravel
… Inverted-roof liquid waterproofing system (upstands) without insulation £6 to 11 / m
… Self-protected PVC membrane on steel decking (not included) with 140-mm- £30 to 40 / m²
thick mineral-wool insulation (standard surface)
… Self-protected PVC membrane upstand £17 to 25 / m

December 2005 BIIN CEA Practical guide - Flat roofs 71

E) Examples of costs and application times
„ Average application times (France) for large-area simple flat roofing
systems, excluding special works, added protection, and insulation
… Standard surfaces
„ Two-ply bitumen system: 0.40 h/m²
„ Bitumen system for roof garden (excluding soil): 0.60 h/m²
„ Liquid waterproofing system: 0.12 h/m²

… Upstands
„ Self-protected bituminous upstand: 0.30 h/m

December 2005 BIIN CEA Practical guide - Flat roofs 72

F -1) French standards and regulations
„ French standards can be obtained from the Challenger documentation
centre or by means of the Intranet

„ Code of practice DTU 43.1:

Travaux d'étanchéité des toitures-terrasses avec éléments porteurs en
maçonnerie (Waterproofing work on flat roofs with concrete loadbearing structure)
… The main reference document for the design and construction of waterproof
roofing or "flat roofs" on a concrete roof slab used to be two documents: code
of practice DTU 43.1 (NF P84-204), dated July 1994, dealing with roofs with
falls of no more than 5%, and DTU 43.2 (NF P84-205), dated May 1993,
dealing with roofs with greater falls.
… These two documents have been merged into one: DTU 43.1 (NF P84-204),
dated November 2004, dealing with lowland climates, i.e. up to altitudes of 900
metres. The provisions of DTU 43.1 (NF P84-204-1) dated July 1994
concerning mountain areas, at altitudes above 900 m (especially Chapter 9)
still apply, in the absence of a new standard to replace them (currently being
drafted).

December 2005 BIIN CEA Practical guide - Flat roofs 73

F – 1) French standards and regulations (cont.)
„ Code of practice DTU 43.3
Mise en oeuvre des toitures en tôles d'acier nervurées avec revêtement
d'étanchéité (Construction of roofs made from ribbed steel decking with waterproofing system):
… Technical specifications - Approved standard NF P 84-206-1 June 1995.
… Special conditions - Approved standard NF P 84-206-2 June 1995.

„ Code of practice DTU 43.4

Toitures en éléments porteurs en bois et panneaux dérivés du bois avec
revêtement d'étanchéité (Roofs made from loadbearing structural timber and wood-based panels
with waterproofing system):
… Technical specifications - Approved standard NF P 84-207-1, May 1993
… Modification A1 to technical specifications
… Approved standard NF P 84-207-1/A1, December 1995.
… Special conditions - Approved standard NF P 84-207-2, May 1993

„ Code of practice DTU 43.5

Réfection des ouvrages d'étanchéité des toitures-terrasses ou inclinées
(Rehabilitating waterproofing work on flat or sloping roofs)
… Technical specifications - NF P 84-208-1 – November 2002
… Special conditions - NF P 84-208-2 – November 2002

December 2005 BIIN CEA Practical guide - Flat roofs 74

F – 1) French standards and regulations (cont.)
„ CSTB 3502 'E-cahiers ' - April 2004 – Specialist group No. 5, Toitures, couvertures
étanchéités (Roofs, roofing, waterproofing):
… Étanchéités de toitures par membranes monocouches synthétiques en PVC-P non
compatible avec le bitume faisant l'objet d'un Avis Technique ou d'un Document
d'Application - Cahier des Prescriptions Techniques Communes de mise en œuvre

„ French standard NF P 37-418 (November 1993)

accessoires de couverture -- lanterneaux (Roofing accessories, skylights)
… lanterneaux d'éclairage zénithal fixes ou ouvrants, en polyméthacrylate de méthyle ou en
polyester armé de fibres de verre : définitions, spécifications, méthodes d'essai

„ DTU 20.12 :
Gros oeuvre en maçonnerie des toitures destinées à recevoir un revêtement
d'étanchéité (Concrete structural work for roofs to receive waterproofing)
… Technical specifications + modification A1 - NF P10-203-1 – September 1993
… Special conditions - NF P10-203-2 – September 1993

„ Th-U rules: Ponts thermiques - Calcul des ponts thermiques (fascicule 5/5)
(revised in 2004) – (Thermal bridging – Calculation of thermal bridging)

December 2005 BIIN CEA Practical guide - Flat roofs 75

F – 2) International standards and regulations
„ Europe – under development:
… DIN EN 1548: Draft - Flexible sheets for waterproofing - Plastic and rubber
sheets for roof waterproofing - Method for exposure to bitumen;
prEN 1548:2005
… BS/DIN/FR EN 14691 / 14694 : Flexible sheets for waterproofing –
Waterproofing of concrete bridge decks and other concrete surfaces trafficable
by vehicles

„ United Kingdom: no British Standard specifically addressing flat roofs.

Each manufacturer produces an agrément certificate (BBA -British Board
of Agrément):
… European Liquid Roofing Association: Code of Practice for the Specification
and Use of Liquid Waterproofing Systems
… Flat Roofing Alliance: Roofing Handbook

„ United States:
… ASTM C981: Standard Guide for Design of Built-Up Bituminous Membrane
Waterproofing Systems for Building Decks
… ASTM 04.04: Roofing and Waterproofing

December 2005 BIIN CEA Practical guide - Flat roofs 76

G - 1) The industry world-wide - Manufacturers
„ Various entities of the group manufacture waterproofing systems:
… Smac Acieroid: bituminous waterproofing membranes, asphalt, and polymer-based
synthetic membranes: http://www.smac-acieroid.fr/
… Axter (subsidiary of Smac Acieroid): for all kinds of bituminous membranes using
modified-bitumens (single-ply and two-ply systems): http://www.axter.fr/
… Resipoly (subsidiary of Screg): liquid waterproofing systems: http://www.resipoly.fr/
„ Other major manufacturers of waterproofing systems include:
… Siplast: http://www.siplast.fr
… Soprema: http://www.soprema.fr
… Meple: http://www.meple.fr
… Sika: http://www.sika-trocal.fr
… Liquid Plastics (UK): http://www.liquidplastics.co.uk/
… Sarnafil: http://www.sarnafil.fr
… Derbigum: http://www.performanceroofsystems.com/ / www.derbigum.fr
… Metactylics (USA): http://www.metacrylics.com/
… Icoper (Italy) – Self-protected liquid waterproofing system used extensively in Cuba:
www.icobit.com
… Bitum (Israel) – Self-protected liquid waterproofing system used extensively in Ukraine:
www.bitum.co.il

December 2005 BIIN CEA Practical guide - Flat roofs 77

G - 2) The industry world-wide - Industry statistics

„ French market
Répartition
Breakdown des
ofprocédés enFrance
systems in Franceinen 2001
2001
(source
(source:magazine SYCODES)
Sycodes magazine)

étanchéité
blown bitume
bitumen oxydé
systems
2%
0% modified bitumen
étanchéité bitumesystems
modifié
10%

12% polymer-based membranes

membranes à base de
polymères
étanchéité
asphalt asphalte
systems

système
liquid d'étanchéité
waterproofing liquide
systems

76%

December 2005 BIIN CEA Practical guide - Flat roofs 78

G - 2) The industry world-wide - Industry statistics (cont.)

„ European market
Surface
Area ofde toiture étanchée
waterproofed roofs en Europein
in Europe en2002
2002
TOTAL
Total == 304
304 million
millionsm²m²

membranes à base
polymer-based
de polymères
membranes
4%
24%
étanchéité
blown bitume
bitumen
oxydé
systems
modified
étanchéitébitumen
bitume
modifié
systems
others
autres (liquid,
(SEL,
asphalte)
asphalt)
7%

65%

December 2005 BIIN CEA Practical guide - Flat roofs 79

G - 2) The industry world-wide - Industry statistics (cont.)

„ Bituminous membranes in Europe

Area of
Surface deroofs waterproofed
toiture étanchée with bituminousBitumineuse
en Membrane membranes inen
Europe
Europe,
enin2002
2002- -Total
Total == 218
218 millions
million m²m2

10%
blown bitumen
étanchéité systems
bitume oxydé
35%

SBS modified
étanchéité bitumen
bitume modifié
SBS
systems
étanchéité
APP bitume
modified modifié
bitumen
APP
systems
55%

December 2005 BIIN CEA Practical guide - Flat roofs 80

G - 2) The industry world-wide - Industry statistics (cont.)

„ Plastic membranes in Europe

AreaSurface
of roofsdewaterproofed
toiture étanchéewith plastics plastique
en Membrane membranes in Europe
en Europe,
en 2002 - TOTAL = 74 millions m²
in 2002 - Total = 74 million m²

PVC
ECB
6% EPDM
6%
TPO
17%
EVA
others
autres

53%

12%
6%

December 2005 BIIN CEA Practical guide - Flat roofs 81

 Architectural trades team

Curtain walling

Laura Doumandji
05214

December 2005 BIIN CEA Practical guide - Flat roofs 82