New roofing materials

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New roofing materials

Baker, M. C.

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'rm

BUILDING

PRACTICE

NOTE

NEW ROOFING PIATERIALS

v

M,C. Baker

Division af Buildfng Research, National Research Council

of

CONTENTS

PAGE INTRODUCTION

ATTACHMENT OF ROOFING HIM8RANES

Loose-laid and B a l l a s t e d Systems Partially Attached Systems

To t a l l y Adhered System Protected Menibrane Systems

TYPES OF ROOFIHG MATERIALS

Synthetllc T h e m p l a s t i cs

Polyvinyl chloride

Po-lye thy1 ene

Polypropylene

Chlorinated polyethylene

Polyisobutylene

Thermosetting Vulcanized Elastomers Polychloroprene

Chlorosulflrnated polyethylene Butyl rubber

Ethylene prapylene diene monomer Modif f ed Bi t m n e

Ho t-applied rubberized asphalt

Modified bftumen or bitumen polymer sheeting~

SELECTING

_AN

NEW ROOFLEJG MATERIALS

by M.C. Baker

ABSTRACT

Several hundred n e w roofing materials have become a v a i l a b l e in the past

two decades. This paper describes the materf als u n d e r three main generic classes: synthetic thermoplastics, thermosetting vulcanized elastomers, and

polymer modif l e d b itmens. Cornparisms are made w i t h conventional roofing materials and techniques, and some considerations necessary for selecting an appropriate roofing sys tern are discussed.

INTRODUCTION

The choice a£ meterfals for roofing is very large. I t includes traditional overlapping w a t e ~ s h e d d i u g materials f o r steeply s l o p e d r o o f s and conventional built-up roofing of felt and bitumen for shallow s l o p i n g

roofs,

In

thermoplastics, vulcanized elastomers and modified bitumens are available in a variety of sheet and l i q u i d forms. The selection process may concern new

b u i l d i n g s or the r e t r o f i t t i n g of o l d e r m e s , qnd owners and designers may be

faced with a great number of options. T h i s paper d e a l s w f t h the

characteristics, a p p l i c a t i o n and performance of several groups of the new materials, and it may h e l p i n reducing the number of o p t i o n s .

The new roofing materials have been classified somewhat d i f f e r e n t l y b y various research and standards w r i t i ~ g agencies, which creates s o m

confueion. A l l the materials are usually referred to as elasto-plastics in the U. S . T h i s f ncludes thermoplastics, elastomers and polymer modified bftumens. Thermoplastic materials are those t h a t can be r e a d i l y formed or changed in shape on the a p p l i c a t i o n of heat. Elastomeric s i m p l y means rubberlike, but an elastomer has been more precisely defined as

a

macrtrrnolec~llat material that can undergo a substantfa1 deformation and return to its o r i g i n a l dimension on removal of the stress. The return t o

the o r i g i n a l dimension is termed the recovery of the material.

Thermosetting materials cannot be reformed or changed in shape on the application of heat.

Synthetic themoplast ics include polyvinyl chloride (PVC)

,

e

(PE) arid polyprdpylene (PP)

,

,

polyisabutylene (FIB). Thermosetting vulcanized elastomers include ethylene

propylene d i m e rnmomer (EPIM)

,

chlorosulf mated polyethylene (CSPE)

.

liquid elastcrplastics available are also p l a s t i c s , rubbers, or p l a s t i c and

rubber modifications of bitumens.

New materials for membrane roofing d i f f e r from the older conventional

(usually 3 or 4 ) of organic or i n o r g a n i c fibre f e l t , b u i l t up on t h e site with layers of bitumen to form a continuous membrane. The p l a s t i c and

rubber sheet roofing materfals are usually a s i n g l e layer of material connected e d g e - t r e d g e on t h e s i t e t o form a continuous membrane. The

m o d i f i e d bituminous sheet materials are usually in two layers t h a t are s t u c k

together and sealed a t the edges on t h e s i t e to form a continuous membrane, The wood f i b r e , asbestos o r glass f e l t s form the reinforcing for t h e bitumen waterproofing in the built-up roofing. For s f n g l p p l y n e w roofing

and modified bitumen roofing, the sheet materials are reinforced i n

manufacture, u s u a l l y with a m a t of g l a s s f i b r e or p o l y e s t e r , and f o r t h i s

reason are sometimes referred t o as prefabricated roofing, even though the

continuous roof t n g membrane s t i l l has t o be produced on t h e s i t e . T h i s i s similar t o conventional r o o f i n g that uses coated asphalt £el t ; t h i s might a l s o b e called p r e f a b r i c a t e d roofing.

The methods of application and fixing u s u a l l y d i f f e r considerably f o r

new roofing materials as opposed to conventional built-up roofing, which

u s e s hot or cold asphalt t o s t i c k the membrane to a deck or to i n s u l a t i o n ,

and t o b u i l d up the layers of t h e membrane. Mherance to t h e substrate m y

be full. or uniform p a r t i a l , and mechanical fastening is required on s l o p e s over 1 :12. S i n g l e p l y n e w materials are frequently l o o s e l a i d on l o w

s l o p e s , but can also be mechanically f a s t e n e d , or partially or f u l l y

adhered. Built-up roofing is l a i d down wirh continuous layers of bitumen

between felts to form the membrane; single-ply materials are joined together by edge l a p p i n g and securing the j o i n t s by adhesive, or by heat or s o l v e n t

welding. M o d i f i e d bitumen sheets a r e adhered w i t h hot bitumen as f o r b u i l t - u p r o o f i n g , or are heated by a flame ( c a l l e d torching) t o produce s e l f - s t i c k i n g .

ATTACHMENT OF ROOFING Ml9BRANES

There are a number of aptions in relation t o the integration o f the

roof fng membrane i n t o a roof iag systea The d e s i g n consideratioas are sowwhat different far the vatlous options, which include loose-laid and

b a l l a s t e d , partially attached, and t o t a l l y adhered sysrems

.

In the loose-laid and ballasted system the membrane is not adhered to t h e substrate at all; it is attached to the roof only at the perimeter and

at penetratfons through the roofing system. The membrane theref ore has t o b e w e i g h t e d down with b a l l a s t f o r protection against wind u p l i f t or membrane

flutter, The _{amount of ballast:} required may be 50-75 kg/m2

(10-15 l b s / f t2) of rounded gravel, or equivalent t r a f f i c surfacing or

landscaping. The b a l l a s t is an extra dead load that mst be allowed far in the design of a n e w roof structure, and must b e carefully considered fn

relation to structural adequacy for any reroofing. Even if the structure

w i l l carry the dead load of b a l l a s t as w e l l as the antfcipated l i v e loads, calculations of d e f l e c t i o n s may be necessary to ensure that

does not cause progressive deflection and p o s s i b l e collapse.

Tmding

Loose-laid medranes are somewhat i s o l a t e d from t h e effects of structural s e t t l e r e n t and movement of the roof deck, because they have

freedom of separate movement, but t h i s a l s o allows them freedom to- s h r h k .

I n some s y s t e m a separator or s l i p sheet may be required to maintain the separation, depending

on

through .the membrane for same materials, but this is probably not very ef f e-cti ye.

Many loose-laid membranes of EPDM are factorylabricated i n t o very large u n i t s , which allows f o r ease of f geld application. The f aetory seams of course are more reliable than f feld seams. In adhered system, these

very large u n i t s are less practical. Partially Attached Systems

A number of techniques are used to secure p a r t i a l l y attached systems.

In

large disc heads of the fasteners.

In

placed over the membrane, and mechanical f a s t e n e r s are driven through holes

in t h e b a t t e n s , through the mzmbrane and i n s u l a t i o n and i a t a Lhe deck. S t r i p s of the membrane are then run over the metal strips to cover and waterproof t h e b a t t e n s and £asteners.

Vertical displacement of the fasteners has t o he considered in r e l a t i o n

t o i n s u l a t i o n board compaction, settlement or other related structural

movement. In some cases t h e fastener heads may push up through t h e

membrane. Partial attachment does not allow t h e c o m p l e t e i s o l a t i o n of the loose-laid system, but it does give adequate freedom for horizontal

movements of the deck and fnsulation, The p o i n t or l i n e attachment g i v e s

resistance to overall wind u p l i f t , but the membrane may still be subject t o f l u t t e r in high w i n d s , resulting in fatigue af the material around the

fastening points. The use of partial attachment by mechanical fasteners,

and a small amount: of ballast is one w a y to prevent this. As with the

loose-laid system, lateral ventlng of trapped moisture f s p o s s i b l e . Totally Adhered Systems

Hat asphalt, cold cut-back asphalt, other cold adhesives, or contact

cement, depending on the material, ar-e used to fully and uniformly adhere the membrane to the substrate in t o t a l l y adhered systems. This method is similar t o that generally used for bi tminous buf l P u p roofing membranes.

For wind or u p l i f t and membrane movement, the totally adhered system is probably best, but local structural movement can cause disruption of the membrane. If a crack occurs in a deck to which a medrane is s o l i d l y

adhered, the membrane w i l l o f t e n crack a s w e l l sfnce there i s not enough unattached material at a crack or j o i n t to absorb t h e mvement. !This can

happen even when the membrane has high elmgation unless the material is thick enough and soft enough t o t h i n o u t , or unless the membrane can shear

away from the substrate near the crack. Whether t h i s becoms a problem w i l l

depend on the total system ef deck, insulation and membrane. Canerally speaking, no membrane should be continuously and r i g i d l y adhered to a

substrate. Closely spaced uniform spot s t i c k i n g is a good compromise

Protected Membrane Systems

In the case of protected membrane roofing systems,2 the waterproof

membrane i s p l a c e d directly on the B tructural deck, either l o o s e l a i d ,

p a r t i a l l y attached or f u l l y adhered, and i s protected by the thermal

insulaticm p l a c e d

on

is exposed; extruded polystyrene f o m appears to do this q u i t e well. The i n s u l a t i o n over the membrane keeps the membrane warm in winter, and protects

it from physical abuse and thermal stress.

If the membrane or t h e insulation is loose-laid, ballast: is required t o

hold d m the i n s u l a t i o n and membrane, and f l o t a t i o n of the i n s u l a t i o n , as

well as wind uplift, becomes a factor. The amount of ballast required may therefore b e greater than for other b a l l a s t e d system. The b a l l a s t mst b e at least equal in weight t o the flotation force on the insulation

( e - g . 100 mm of polystyrene i n s u l a t i w w i l l require about 100 kg/m2 of

b a l l a s t ) . A p a r t i a l l y or f u l l y attached ~ u t b r a n e should function well in

t h i s system because temperature variations at the deck w i l l b e small and the p o s s i b i l i t y of movement and membrane s p l i t t i n g less. This would a l s o allow

for attachment of the insulation t o the membrane, and cut down on t h e amount o f ballast required. For meuhrslles that do n o t cure completely, such as hot

applied rubberized a s p h a l t , attachment of i n s d a t i m to t h e membrane i s undesirable because insulation movement might damage the membrane. A separation sheet is required in such cases.

TYPES OF ROOFING MATEBIALS~

S y n t h e t i c Themoplastics

Polyvinyl chloride (PVC) is produced in Europe and the United States in rolled sheet form 1 t o 1-5 mm thick (usually 1.2 mrn) and is sold in Canada by a number of companies, Some products are resnfarced w i t h g l a s s f i b r e or

polyester; other products are n m r e i n f arced. The materf a1 has good resistance t o creep and can be easily solvent- or heat-lded t o itself, makzng i t practical f o r field f abrfcation of a roofing membrane. The solvent is tetrahydrofuran.

PVC is often a p p l i e d as a loose-laid system with no attachment t o the roof deck o r insulation. It is kept i n place only by attachments a t the roofing terminatfws and around penetrations through the roof, arid b y a

layer of rounded gravel or other b a l l a s t . The b a l l a s t also protects the underlying membrane from ultraviolet radf atf on and other weathering. Partially attached systems can be used where roof s l o p e or s p e c i a l

c o n d i t i a n s prevent the use of heavy gravel ballast. Attachment is usually by mechanical fastenfngs. For so= systems special fasteners are driven into the deck through plates or discs s e t on top of the insulatfon. The

d i s c s are PVC coated and the PVC membrane can b e solvenFwelcted to t h e m This allows for some membrane movement, but secures the membrane and insulation against u p l i f t and s l i p p a g e down s l o p e s ,

Metal bars can also be placed on t o p of the membrane with f a s t a e r s

passtng through them and through t h e membrane and i n s u l a t i o n t o the deck. The bars and fasteners are then covered w i t h a s t r i p of PVC that is adhered

or welded to the membrane. b t h of these mechanically fastened systems

s t i l l may allow t h e membrane to f l u t t e r between t h e fasteners when wind is blowing over the roof, Where this cannot be tolerated, it may be necessary

to provide f u l l adherance. In t h i s case the e n t i r e membrane is bonded with adhesive t o its substrate. If it is over insulation, it may be mechanically

fastened and bonded as well. The f u l l y adhered system functions l i k e a f u l l y adhered cunventicanal built-up roofing syetem, and can accomodate 6nly a l i m i t e d amount of substrate movement,

Nun-reinf orced

W C

flashing d e t s i l s . Reinforced PVC is mch less likely t o have any shrinkage

problems. Details for any specffic material m e t take t h i s factor i n t o

account. Sometimes a fold of extra matefial is provided at the b u i l d i n g

perimeter before the roofing is turned up and anchored t o the perimeter

d e t a i l . T h i s allows the roofing membrane to contracr inward toward the centre of the building without creating a p u l l i n g force on t h e anchorage

p o i n t s *

The permeance of PVC membranes is claimed to be several hundred times

that of built-up roofing and many times that of modified bituminous

membranes, and i t is also claimed that moisture in a roofing system can dry

out by d i f f u s i c m through the PVC material, For this reason it is

recommended by f ts proponents for use over exfsting w e t roofing systems. Drying through the membrane by diffusion i s l i k e l y to be extremely slow, b u t some a d d i t i o n a l drying might be achieved b y venting t o the space under a

loose laid membrane, i f moisture can move laterally to the vents. Even i f

not much drying occurs, a new menibrane and additional insulation w i l l give same relief from e x i s t i n g problems and b e t t e r energy conservation, and t h i s may be a viable approach, providing full consideration is given to the

possibf l i t y and consequences of further deterioration of the o l d roofing.

The workable temperature m i n l m m for PVC is claiaaed to be -15'C or

lower, Even if t h e material is f l e x i b l e at such l o w temperatures and can

stand the rigors of cold application, there

is

higher temperatures is more desirable. Since human discomfort is involved at the lower temperatures, the level of careful workomship required f o r the assembly of such materials i s unlikely t o be present, unless the work can b e carrfed out under shelter,

FVC has good resistance to weather and chemicals generally, b u t is

adversely affected by coal tar, asphalt, o i l s and animal f a t s . When used

over o l d biturdnous roofs, it

msc

f ram built-up roaf ing below. Oils used f o r servicing equipment during a p p l l c a t i c m , and heatfng, ventflation and air conditioning equipment i n service may a l s o damage the material.

Polyethylene is used in roofing but is difficult to adhere, and i s

normally n o t a p r i n c i p a l material in roofing system, It does form p a r t of several composite sheet roof 3ng system as a reinforcing, a carrier or a

Polypropylene is the polymer used

far

asphalt systeum. T h i s is usually t h e a t a c t i c type, - - . whfch is a residue from

the manufacture of isatactfc pol$propylene. It is also used in the

production of roofing fabrics i n sheet form, f o r s l i p sheets or stone separators fa protected membrane roof systems.

Chlorinated polyethylene is composed of high molecular wefght and low density polyethylene that has been chlortrtated to give - it good - weathering -

and chemical resistance t o acids. CPE normally does a o t require a

plasticizer t o g i v e it flexibility, as do som of t h e other materials, such as PVC, 'It is used as a a i n g l e p l y roofing sheet in thicknesses from 1 to 2.2 mm. S i n c e most CPE does n o t have a plasticizer, it f s compatible w i t h

bitumen, and has better weather resistance than materials havfng

p l a s t i c i z e r s . It i s applied 1 o o s e l a i d , adhered, and Wchanically fastened. Seams are generglly heat-welded.

Polyisobutylene (PIB) i s a thermoplastic copolymer composed of isoprene, isobutylene, carbon black and aging protectors. It is more

soluble and rubbery than polyethylene and polypropylene, and general1 y has b e t t e r weather resistance and more l o w temperature f l e x i b i l i t y . FIB is

vulnerable to creep unless reinforced wlth a backer or compounded w i t h o t h e r

polymers. It is n o m l l y available w i t h a non-woven polyester fleece backing, which serves as a reinforcing and also as a cushion when applied aver rough s u b s t r a t e s . The PIB is usually about 1.5 mm t h i c k , w i t h backing

about 1 mm, and is used as a single-ply roofing sheet, I a p s are sealed w i t h a bonding tape, ar by solvent welding, It can b e used as a l o a s e l a i d

system or as an adhered system using hot biturnen or bituminous-based cold adhesives.

Thermosetting Vulcauized Elastouers

Plastic-like materials consisting of individual hydrocarbon chains can

be changed t o elastomers by t r e a t i n g them w i t h sulfur, heat and pressure, a

process called vulcanization. Vulcanization makes t h e polymers e l a s t i c and

eliminates creep. Chemical bands are f o m d by the curing and once set, t h e materials retain their original shape, even after heating. They a l s o are

insoluble and very d i f f i c u l t to adhere to. To improve the adherence, some materials in this c l a s s are p a r t i a l l y cured in manufacture, and full cure is

completed by aging and weathering in use. Since they are v e r y strong and

tough and do not creep, the thermosettfng materials are not usually

rein£ orced.

P o l y c h l o r o p r w e ~ better knom by its trade name "neoprene", c o n s i s t s of

hydrocarbon molecules w i t h some chlorine atoms present. A whole group of

t h e chloroprene

'mere

'

,

polychloroprene polymer.

In

as the base pblymer in 'contact' cement and it is also formed i n t o partially cured sheet material to be u s e d as flashing. It gradually cures when

exposed to heat In use t o become a f u l l y vulcanized material. Fully

v u l c a n i z e d roofing membrane sheets are a l s o produced. T h i s synthetic rubber

has good resistance to petroleum oils, s o l v e n t s and weathering, Since it is usually black, a protective and colour coating of chlorosulf mated

polyethylene is recommended by some manufacturers. Neoprene s h e e t

thicknesses range from 0.75 t o 3 mm, but those used f o r roofing a p p l i c a t i o n s

They are applied loose-laid, mechanically fastened, or f u l l y adhered. The sheets are l a p joined with contact adhesive, and contact adhesive is also used in the f u l l y adhered system for attachment to a deck or to

i n s u l a t i o n . &cured neoprene sheeting is used f o r flashings because the uncured material w i l l conform and adhere t o sharp bends, which the cured material wf 11 n o t do. Complete curing can take place with aging, Thorough and complete sealing of a l l lap j o i n t s and flashings i s c r i t i c a l and fn order t o achieve good adhesion, the laps nust b e clean, which f o r some

systems w i l l require solvent cleaning. Although neoprene materials

t h e o r e t i c a l l y can b e a p p l i e d a t cold temperatures (below 5 * ~ ) , i t I s not practical to work at much less than 1 5 ' ~ . Cleaning solvents and l a p joint cements are flammable, making smoking or open f i r e s a high hazard during

application.

Chl~rosulfonated polyethylene is a chlorinated polyethylene containing chlorcrsulphmyl groups combined with high m o l e ~ u l a r weight, low density polyethylene. Better known by i t s trade name "hypalon", it is used in

liquid form as a colour coating f o r other conpatible materials. 'It is also produced in roofing sheets about 1 mm thick, including an tntegral backing

sheet or reinforcing core. It can be used a s a t o t a l l y adhered system with

appropriate a d h e s i v e s , o r with mechanical fasteners only. Laps are s e a l e d by hot-air or solvent welding. Solvent welding has temperature limitations, and the material weathers by 'chalking', which could be objectionable.

Butyl rubber is obtained by blendfng 'mers' of isoprene with 'mers' of fsobutylene and vulcanizing the blend. Pure i s o b u t y l e n e and polyisobutylene cannot be vulcanized. Butyl rubber was produced some years ago as a sheet roofing membrane, b u t i s n o t widely used today. Many e a r l y f a i l u r e s

occurred with lap joining using rubber adhesives. Chemically unlike natural

rubber or o t h e r s y n t h e t i c elastomers, b u t y l rubber is inherently resistant

to ozone and corrosive chemicals. It is used as a b l e n d i n g agent in some of the EPW sheets to improve t h e i r b o n d a b i l i t y and seam strength.

Ethylene propylene diene monomer (EPDM) is compounded from ethylene and

propylene hydrocarbons, which are copolymerized with d i m e s so that they can

be &lcanized i n t o a f u l l y cured rubber. The EPDMrs are especially

resistant t o ozone and u l t r a v i o l e t l i g h t , and consequently have an advantage

over some other elastomers, which can b e degraded f a i r l y rapidly by ozone

and u l t r a v i o l e t . Most of the EPDM membranes used in roofing are 1 or 1.5 ma! in thickness, w i t h the thinner material used for ballasted loose-laid

system, and t h e thf cker material for adhered exposed systems. EPDM is n o t usually reinforced and sheets are normally b l a c k . The material is r e s i s t a n t to many corrosive chemtcals, b u t n o t t o petroleum products. It cannot be

solvent- or heat-welded, and the sheets must be j o i n e d together at l a p

j o i n t s with contact cement or with uncured EPDM rubber rapes. In the

adhesive method, t h e material =st be cleaned of all talc or d u s t , and then

b o t h surf aces to be joined must b e coated with adhesive. When t h e s o l v e n t in the adhesive has escaped, the l a p is mated and p r e s s e d together t o form

t h e j o i n t . When the sheets are being adhered t o a deck or i n s u l a t i o n , a technique of folding has to be worked out so that the adhesive can be

applied to the EPDM and substrate and t h e EPDM worked smoothly back into position. The material can be factory fabricated into very large sheets t o

cut down on or e l i m i n a t e field lapping, b u t t h i s introduces a d i f f e r e n t handling problem for t h e system, It would be more advantageous for a

for winter construction, where heated protection would only have to be provided

for

The EPDM may be loose-laid and ballasted, it may be p a r t i a l l y attached by mechanf cal fastenings in a variety of system, or it may be f u l l y

adhered. Metal bars are coarrmonly placed on Cop of the membrane, w i t h

fasteners penetrating the membrane and fnsulatlan, t o fasten into the deck.

A strip of EPDM covers the bars and is adhered to the membrane. Other

systems of fastening with bars a n d buttons do not require penetration of the membrane. 'Ln t h e mechanically fastened systems, t h e membrane will still be subject t o fluttering under wind c o n d i t i o n s , and it may be necessary t o u8e

some combination of mechanical fastening, adherence and ballast. Flashings are constructed using the same material as the membrane or using p a r t i a l l y

cured EPDM or neoprene,

Modified Bi tu- s

The term bitumen describes resldues from the processing of petroleum, called asphalts, and residues from the distillation o f coal, called coal tar pitches, Host of the modified bituminous materials are based an asphalt.

A l l asphalt used in raoflng is modiffed to some extent, bemuse straight run

asphalt is not suitahle for roofing as it comes from the petroleum

processing. It has t o o l o w a softening point: and would be a poor binder, with t o o mch flow at t h e high temperatures that occur on roofs; it 5 s a l s o

very b r i t t l e at l o w t emperaturas. The useful teqerature i n t e r v a l for bitumen can be Increased by s t a b i l i z i n g the marerial b y oxidation

cross-linking. T h i s technique is called blowing with eteam, and b 1-

bitumen w i t h several ranges of softening p o i n t s is used i n traditional roofing systems. A s p h a l t s have also been modifled w i t h f i l l e r s , which

greatly affect the flow properties. Combinations of fillers and s o l v e n t s

produce asphalt cement far f l a s h i n g s , and a variety of roof coatings.

E m l s i f i e d asphalts use small p l a t e l i k e particles of mineral such as d c a or bentonire clay with a water or chemical carrier, AT1 of these

traditional modifications t o asphalt have increased the u s a b i l i t y and

weatherability of the materials.

More recently asphalt has been modified by the addition of polymers t o

produce materials with better resistance to f l a w , high elongation, and better fatigue resistance. In the coxpounding of modified asphalts,

polymeric networks are created w i t h i n the bitumen, which markedly change the characteristics of the materials, The polymer systems used by different

producers vary from natural rubber to more conplex synthetic s y s t e m such a s

b l o c k c o p a l p r s and polymer b l e n d s .

The polymers used at: this time include styrene butadiene styrene (SBS),

atactie polypropylene ( A P P ) , ethylene v i n y l acetate (EVA), styrene butadiene rubber (SBR), ethylene propyleae rubber (EPR) or (EPDM) and neoprene. The

t w o p r i n c i p a l modifiers f o r sheet materials, however, are SBS and AFP, _They are quite different, and produce quite d i f f e r e n t products, even though they

appear to be similar. F i l l e r s and process oils are used to extend and s t i f f en the products, to give increased mechanical strwgth and improved f l o u resistance, or t o improve workability in processing, and special additives may b e included t o impart parefcular properties. Most sheet materials are a l s o reinforced with glass or p o l y e s t e r fleece, and some are manufactured with carriers such as p l a s t i c films, mats or f o i l s . The

modified materials do not have s i g n i f i c a n t l y b e t t e r weather resistance than

unmodified bitumens, and many therefore use a surface t r e a t m e n t on the cap

sheet for the system; t h i s may be granular material o r metal f o i l . For materials without surfacing, it I s necessary t o a p p l y gravel o r other protective cover.

Hot-applied rubberized asphalt is a b l e n d of rubber, asphalt and fillers t h a t is a p p l i e d about 4-5 mm t h i c k t o f o m a continuous adhered

membrane without reinforcing, except for f l a s h i n g s a t details, Joints i n t h e substrate and flashing d e t a i l s n e e d r e i n f o r c i n g such as nylon o r

polyester, or elastomeric sheet material snch as b u t y l , EPDM or chloroprene

rubber. The h o t material is poured o u t o n t o a deck and manually s p r e a d to

the required thickness to g i v e a totally adhered continuous membrane.

Rubberized asphalt of t h i s t y p e is d e t e r i o r a t e d by exposure to s o l a r

radiation, and its use 1s confined t o the protected membrane mode, where it

is p r o t e c t e d by t h e i n s u l a t i o n and g r a v e l or other surf a c i n g above i t .

The material remains q u i t e s o f t , so it can s t r e t c h a n d thin o u t to

accornodate crack or joint movements. I n s u l a t i o n a p p l i e d over i t , however,

may adhere, and subsequent f l o t a t i o n or movement of t h e i n s u l a t i o n can damage the membrane. For this reason a separation sheet i s g e n e r a l l y u s e d

to ensllre t h a t the insulation does n o t s t i c k . The insulation must b e h e l d in p l a c e by a b a l l a s t of gravel, t r a f f i c surfacing or landscaping.

If there is any dampness on the roof during application, the h o t material will foam, which can lead to pinholing on the cured material. A

primer is used cm the deck, but it doesn't always achieve complete coverage, and of course d o e s n o t prevent moisture from b e i n g deposited on t h e primed deck surface. The e x t e n t of the pinhole problem depends on the amount of

moisture, and m3ld foaming might n o t even be n o t i c e d by the a p p l i c a t o r s . P i n h o l e s can be closed b y t h e weight of i n s u l a t i o n and b a l l a s t on top, b u t this does n o t necessarily happen i f these are placed some t i m e a f t e r t h e a p p l i c a t i o n is finished.

The rubberfzed asphalt, as a f u l l y adhered membrane, has the advantage

t h a t any d r i p p i n g from a l e a k w i l l l i k e l y b e d i r e c t l y below t h e defect on

the roof a n d can be e a s i l y located. This applfes to any f u l l y adhered

protected membrane a s compared to l o o s e l a i d or a b o v ~ i n s u l a t i o n conventional membranes, where a d r i p i n s i d e the building mag be from a

membrane or system d e f e c t at a cansiderable d i s t a n c e from the d r i p .

Modified bitumen or bitumen polymer s h e e t i n g s are produced in rolled sheet form and are u s e d t o f i e l & f a b r i c a t e s i n g l e or t w o - p l y roofing membranes. A base sheet of conventional bituminous felt may be used w i t h

some system. They are mostly r u b b e r m o d i f i e d asphalts o r as phalt-mod1 f i e d rubbers, reinforced with glass or polyester mats, a l t h o u g h some have u s e d

treated j u t e , and some have a carrier of polyethylene, and surfacings o f granules or metal f o i l . The finished f e l t s are f a i r l y s u b s t a n t i a l , with

thicknesses ranging from 1 t o 4 mm. The polymer modification increases tensile strength of t h e newly manufactured felts. Ritumen polymer membranes may have t h r e e times the strength of organic f e l t b u i l t - u p r o o f i n g , and have

much greater flexibility, with an e l o n g a t i m before breaking from several

times t o several hundred t i m e s t h a t f o r conventional f e l t s . These v a l u e s ,

however, may he much less for some materials, a f t e r a short aging time, than

e l o n g a t i o n t o break for APP modified asphalt may drop o f f considerably w i t h

aging, and cracking of the material may be a problem at cold temperatures.

Most systems were d e s i g n e d as two-ply roofing, and when used in t h i s

manner the f i r s t p l y is a non-surfaced sheet, of t e n thinner and l i g h t e r than the cap or weather p l y , which usually has granule or metal foil surfacing. Some manufacturers reverse the approach and make t h e base sheet t h e thicker one, More r e c e n t l y many o f these materials are being promoted and sold as single-ply systems, Since they are b a s i c a l l y bituminous, they can b e embedded in hot bitumen or biturnfnous mastics, bur since they are also thermoplastic, they can be heat-welded. They can b e corqounded to b e

self-adhering, or can be self-adhered by heating w i t h hot air o r a flame.

Application by s e l f - s t i c k i n g or torching, or a combination o f t h e two, has

considerable advantage for roof c o n s t r u c t i o n in cities, where g e t t i n g

materials to the site may be d i f f - l c u l t or where pollution from asphalt

h e a r i n g kettles could be a problem. The greater hazard from using torches

on the roof has to b e considered and a p p r o p r i a t e s a f e t y precautions taken.

The h e a t i n g can be critical, and underheating or overheating may result in

an unsatisfactory edge a r end l a p . APP modified a s p h a l t i s the r y p e most commonly used f o r torching.

Although modiffed bitumens are usually solidly adhered to the

substrate, they can a l s o be applied a s l o o s ~ l a i d system with b a l l a s t or in

t h e protected membrane mode with i n s u l a t i o n and b a l l a s t . The self-adhesive,

p r e s s u r e s e n s i t i v e sheets are very t a c k y , and will s t i c k to themselves or to

a clean substrate when the paper backing that prevents s t i c k i n g in t h e roll

is removed. T h i s has been d e s c r i b e d as 'ban&aid' t y p e roofing, and i t s u f f e r s from the same problems that 'band-aids' have. &ithex w i l l s t i c k t o

d i r t y , wet o r frozen surfaces. Preparation of the deck or other substrate

t o provide a clean, dust- and moisture-free surface is of great importance.

F o r such systems a torch may be used for s o m e of the f l a s h i n g work a r

details.

While reinforced m o d i f i e d bituminous sheets appear t o b e a d e f i n i t e

improvement over previous m o i s t u r ~ s e n s 2 t i v e f e l t s used f o r conventional b u i l t - u p bituminous roofing, they do n o t have an e n t i r e l y problem-f ree

record. S l i p p a g e in bitumen adhered jobs has occured, presumably because of

an _{improper choice of bitumen. Also unsealed edge or end laps have allowed}

water penetration, Sometimes t h e l a p s were n o t sealed during a p p l i c a t i o n , and sometimes the l a p s f a i l e d i n service. Systems u s i n g metal foil weather

s u r f a c i n g have had corrosion from c h e d c a l s , and p e e l i n g and puncturing have

occured. Contaminants such as o i l for roofing equipment during a p p l i c a t i o n , and r o o f t o p heatlng, ventilating and a i r conditioning equipment In s e r v i c e , as well as a c i d s and sealers have affected the material on some roofs.

Flashings are generally similar in detail to those in b u i l t - u p roofing, and

s u b j e c t to the same deficiencies of design and application.

SELECTING AN APPROPRIATE ROOFING SYSTEM General Consfderations

Most of the new roofing materials are s u p e r i o r in some ways to

conventional bituminous materials, b u t many also have sonre l i m i t a t i o n s . In choosing an appropriate material and system it is necessary to consider

economics, quality, aesthetics, application and service l i f e . Piany of t h e s e considerations are f nterrelated. Ease of a p p l i c a t i o n and e a s e of repair have a d e f i n i t e effect on the overall economy and m l i f e c y c l e cost ( t h e

i n i t i a l c o s t p l u s maintenance over the service 11 fe of t h e material).

Smooth surfaced roofing is generally easier t o repair than roofing coveted with gravel or other surfacing. Aesthetics is a relative consideration and

will be very m c h affected b y deterioration and ease of repair. Many of the new roofing materials are easily repaired by parching, b u t if t h e roof is

v i s i b l e it may lose its aesthetic advantage when covered with patches,

Service l i f e needs particular consideration, and new materials s h o u l d n o t b e

s i m p l y compared t o conventional materfals. Bnything less than t e n years fs

obviously not a s a t f s f a c t o r y service l i f e and even t h e twenty years a s c r i b e d to c o n v e n t i o n a l roofing is still well below t h e f i f e of an average building or even the term of its mortgage.

Costs of materials and systems vary with geographic location, and t h e complexity of the b u i l d i n g d e t a i l s . Tn general t h e f frst: cost of many o f

the new roofing materials and systems is greater than for an equivalent conventfonal bituminous b u i l e u p roofing system S o m e are much more

expensive. Single-ply elastomeric roofing and modified bituminous roofing s y s t e m as s i n g l e p l y s are approximately t h e same, or only slightly hfgher in cost, than b u i l t - u p roofing. Experfence with modified bituminous roofing

in Canada seems t o i n d i c a t e t h a t s i n g l e - p l y applications of this material

are not as dependable as two-ply systems. Hot-applied rubberized asphalt

used i n a protected membrane roof on a concrete deck may b e cheaper than b u i l t - u p roofing. So Ear t h e r e has been very little reported assessment of

the l i f e cycle costing, but some of the new roofing systems have g i v e n many

problems in t h e first: few years of use, and some have been replaced after a few y e a r s of troublesome service.

Most new roofing materfals are factory finished sheets referred t o as prefabricated roofing; they appear t o be of much h i g h e r q u a l i t y than asphalt soaked f e l t s , which are merely t h e reinforcing for t h e f i e l d - a p p l i e d asphalt

used t o b u i l d up a r o o f i n g membrane. Ia general the d e w factory produced membranes do have good strength and elasticity in particular, but some are a l s o e a s i l y punctured, c u t , burnt or deteriorated by common cmtamfnants.

Hany of the new roofing materials are aesthetically pleasing when smooth

surfaced and coloured, and this may b e a d e f i n i t e consideration when a roof

is exposed and h i g h l y v i s i b l e . It is not a consideration when the material is used in a ballasted or protected membrane roofing s y s t e m

There are a p p l i c a t i o n advantages for almost all of t h e new roofing materials. S i n g l e p l y roofs have obvious advantages over m l t i p l c p l y

roofs. A roll-on or spray-on l i q u i d roofing has an advantage on

unusually-shaped roofs. S e l f - a d h e s i v e or torckon systems also o f t e n have

advantages over systems that require asphalt heating and d i s t r i b u t i o n on the

roof. There may, hawever, b e limitations in some of these a p p l i c a t i m procedures. There is no margin for error in a slngle-ply system. The

material, j o i n t s and details must be perfect t o start with, and s t a y perfect in service. The level of careful workmanship required, however, does seem

t o b e a v a i l a b l e i n the industry. Dust, c o n t d n a n t s and moisture can a f f e c t the self-adhesive materials, and under- or over-heating, t h e torch-on

system. If s i n g l e laps are n o t s e a l e d or e a s i l y separated, the roof will

Building considerations

When a new building is being designed the selection of the roofing material is n o t as d i f f i c u l t as for an e x i s t i n g b u i l d i n g being retrofitted. For the new building, d e t a i l s can b e prepared that

are

stiffness .and load carrying capacity of

the

aspects of the building can be eaaily planned or m o d i f i e d during the design

stage. An analysis of t h e requirements in relaticm to the c o q l e t e system and t h e particular environment can determine what properties are of

particular 1mport.auce to the choice of materials and systern. T h i s analysis should include a consideration o f the compatibility between separate

materials i n the rooffng system.

An existing b u i l d f n g can seldom be modlf ied w i t h regard to load

carrying capacf t y and other d e t a i l s ; thus the choice of roofing system is much more l i m i t e d . Sometimes even the o r i g i n a l drawings, 8pecf f ications and d e s i g n calculations are n o t avaflable to determine the load carrylag

capacity of the structure, which is a critical cmsideration for b a l l a s t e d

systelrrs of any sort. For many existing b u i l d i n g s t h i s may e l i m i n a t e a p r o t e c t e d membrane roof system or a loose-laid ballasted membrane,

In

cases the o l d roofing should b e coqletely tom o f f and a new I i g h F w e i g h t

smooth surfaced roofing system a p p l i e d t o the cleaned structural deck. If

the roof ponds water, b e t t e r drainage should be an a i m I n any r e t r o f i t ,

although t h i s may not always be practicable, The only way to achieve a

s l o p h g roof in that case may be t o use t a p e r e d ineulaticm. F i l l s can be used, but there is greater a p p l i c a t i o n hazard and greater weight, and they are s e l d o m s u i t a b l e when the exfsting roofing is left i n place.

An existing roof with a history of splits due t o b u i l d i n g or membrane

movemnt may b e a candidate for one of t h e l o o s e l a i d elasromeric system*

If the roof cannot carry the weight of b a l l a s t required, it may be p o s s i b l e t o use a mechanically fastened type. When an existing roof has been damaged

by physical abuse such as heavy maintenance or other t r a f f i c over the roof, the abuse can be restricted by the use of a proper walkway system f o r the

new roof, Otherwise, any new roofing membrane may suffer damage s i m i l a r to t h a t on the o l d roofing. Where a protected membrane roof is practicable, it provides a great degree of protectfon t o any r o o f i n g membrane.

1, The Supplement to the National Building Code of Canada, 1980.

Commentary I

-

Code, National Research Council Canada, O t t a w a , NRCC

17124,

2. M.C. Baker and COP. Hedlin, 1972. Protecte&Hembrane Roofs. Canadian Building D i g e s t 150, Mvision of Building Research, Watimal Research Council Canada, Qt tawa.

3. Index to S i n g l e Ply S y s t e m , The Roofer' e Magazine, D & fi Publications