When to re-roof

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Booth, R. J.

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When to Re-Roof

Booth, R.J.

NRCC-40627-4

Building Better Roofs: IRC Technical Seminar, 11 Cities Across Canada, September 1996-February 1997, pp. 1-19

When to Re-Roof

'Ibis s d a r discusses

d

s

fmn the viewpoist of

tbeir

design and f i m d d

m.

Typical oudast typical mofs and, as a les& mof r m n s m t

~~~

rm&amx,

re@ and the timly replacement d m f h g systems.

In

this p a p wc discuss r ~ m f i a g .

are may di&xent Qpes of low-sloped m f m g systems- This p q e r

-

an r e - m k g & d d n s for con ventional lw-sloped &g these have thamd ins-n

underneath built-up, mdSed bitumen

-pb

-.

The paper is mganidinto four d m :

background s-tics abut m n d o n a l low-sloped rwf systems.

a Estmical background to show why ;and how such rwf systems have changed

fmding mof ,*I blisters in built-up roo&, and steel deck mmsim NEW ROOFS AND RE-ROOFTACG STATIS-

Construdm af bddb&rr in Cansada grew rapidly through the first three quarters of this century and peaked in 1W3.

New

n o n - r e d d d canstnrction b t y ~ E W to U] m o n q u m metres in

];a73 but by 1991 it had

fallen

to 7 million square metres. MjWhg annual e o nstatistics to smooth out qdes

of

economic growth and reassion, new industrid, mmmcial and

~ ~ b a i l d i n g h a s ~ e d b y a b o u t 2 % ~ ~ o v a t b e h t ~ y ~ ~ ~ ] .

~ i g ~ r e

1

s a i c s

i n d i m idmid, cpnrmrrcial and institutional consmaion bas declined ov%r the k t 20'yeam

25- ,- , n = 'Ef Y 5 - Year

In 1991, Censas d stat^ data

w m

I] i m h f d that half

of

the x&&nW dvellingsinCsnadawercc~ostmcf.d~orto 1965,aaddmthalfd~enoa-ddmthlhiIding

stmk was c o n s ~ c t e d prior to 1972, Because of the

Iarge

volume of adsting bnilding stock and the small volume of new no*~sidenthl construction, m-roofing activity accounts for b u t 76%

of mfs h i l t wday.

New r m f s (2% of stuck) = 2 98 old m f s with 15 year life cycle = 98/15 = 6.53

A recent m e y mdmtaken

in

the

US

mkmm21 indi& that re-mfing accounted for 75%

of low slape "commacZ mfing in 1995.

In

this survey, re-rwfmg was further b r o b

down

into replacement (46%) axld recoyer (29%).

A k w dehitims help:

Maintenawe: Ao-active m n i h g aad preventative repair

of

xoofs before p r o b h

arise.

Recovec hying a

new

roof rnembhane

ova

an entire roof, wid^ or without remOYItl of the old roof membraned

&phamm: Complete rum4 of the okl m h g system to mof deck level and

replac.Rment

with a new roofing system.

Reds hcludes both Roof Re-cover and Roof Replac- but not Roof Repair.

O n e ~ ~ o f ~ r 0 0 f i n g i s t h e ~ ~ ~ ~ O I B r 0 0 f s a r e q W ~ u s e o f problems, and when the causes

of

these pmblems ate hciwn and

~~

replacem& roofs

can

be

chsen with a view to overcodng aay w a k w s m that caused the old roofs

f

d

Statistics h m a survey of aver 12,000 roofs in the

US

mfemmce 31 -indime that replacemeat roofs have f e w e r p b k m

d m

raew

m f s . Hwwer this

is

the

m e

only w h the old roofs are fidlyremovled d r e p k d Whm oldroofs a r e r e - c o v d with a rmew mdmm,problems are m p o m d r a h w - b y ~ m .

New

R q h e m a t (tear off & rephe)

lative P I D b Ratio D e r

R d

1.00

U n f m y , the y t a g e of =cover, as

opposed

to complete m m d and rephment of old roofs, has immasd Tkm are good embmmmW reasmu for xemvahg roofs, and re- cwer can alm be the best a m m i c option for

-

roofs when the canses of problems have k p m p e d y ~ z e d m d d e a l t ~ i n t h e n e w r o o f ,

If

overed m f s ]Itst sabstaddy k s than removed and replaced

x w f s

rhen both enviTlonnnentaland~csaPFin&safl=~~~~.zheprimaryfocusshouZdberoofp~e, true ~ 0 m y a n d u l ~ ~ s a e w a x d s h i p S t u n f r o m ~ l a s t i n g I O O f s .

ROOF

UFESTA77STYCS

In lW0Stathia C a n a d a i n ~ n e w e s t i m a t e d h k h 4 9 categories of indusaial and h t i t u h d c o m c t i o n 41. AsGording to their m e y of owners, e x p c t d & e e l i v e s ~ b y 2 0 t o 5 U % o v e r t h e b t y y e a r s b 1947to 1987.

The C a d h Standards A w x i a h n S478-95 "Weline on Ducddity h Buildings" suggests

e g n service lives for hddhgs aad h U n g assembljes such as foudahms, walls, raofs, etc. (See Table I) Wertmce 51.

Table I C a w r i a of Design Semi= Life for

B13-

The C- Smndards Assa&icm @Wne listg t h e . M g n sewice bfk for a singbply m e ~ ~ e r r o o f w e r r i g i a i n s u I a t i o n m a ~ c o n ~ ~ k ~ 15y-

S p c d f i ~ ~ s o f ~ e l o o ~ ~ s r e ~ r n b ~ ~ ~ e k ~ d 3 to15gears

(see Table

a,

a

point

that the d fbr

on-

d m a w e . Idbmmion about the

~ s o f ~ a n d ~ e m a i m m a n r e o f ~ s s s c l n b l i e s i s ~ e d i n t h c ~ S t a d a d s Associatitrn gdebe

On

this basis typical medimn life hddhtgs will be mmfed once or twice, and longer life hddhgs wifl be ~le-roded many times.

SoIreplacemymofQ 15 ~ r i g h t ? Wellperfiapsmr & - ~ g i s a n s e s s a r y p a r t o f b d h g mamgment and it s h d d oerer be an koWxi or rmpdiEtable event. Re-m&ng should

~ a f t a p ~ ~ ~ c e b e n a n e s ~ m m a e e n p e a s i c r e m m m e c a r r y i n g m r t o f a new

&.

A mf will last

as

lmg as the owner decides, and it will be re-roofed when the owner

2. Rmfs can last f?om less than one year to m m than sixty years.

3. B m i d y , built-up roof membraxles were expectd to last 15 or 20 years. This expectation was k g e y

based

upon 15 and 20 year w m t i e s provided by manufacturers of 3-ply or $-ply built-up mofing membranes. Records show that 15 and 20 year life expectancies were routinely achieved for Wt-up roofs consttucted up to 1958; the year that xoof bonding tamhated in Canada Ipefermce 6J.

4.

On

average, m f s mnstsucted today do not last

as

long

as

they used to.

Surveys abut roof longevity must k q d because roof roof failure, and m&ng problems are often dehd differently.

Also

roof q h m m e n t periods can be misleading when roofs are r e p l a d for reasons other than lack of pafc- (eg- pmmatarely for building expansim, or tardily because of lack of funds).

A 1985 study of built-up roofs owned by the Ontario Ministry of Housing s h o d a r m f replacement ~ l

of

e12

years

(see Figure 2) ~ I P 71. Facility C ~ managers of some large

Canadian private and pubk wganizations have rep& average roofing replamrent

cycles

between 10 and 15 years. Private communications

from

fmeign roafing organintiom suggest that

US

mfs have similar Life cycles, but Earopean mofs are bought to

Iast

longer.

figure 2 Oatario Housing Capodon study of the age of a r o d whm it was replacd

F h f Age

R m t smisticaI srrrveys on roof pmblems

and

failures W c a t e that 62% of

US

roofs e x p i e n d problems in the first year of life axld 99% of US roofs experienced same problems in the first 10 years (see figure 3) mference 31. Statistics knn the UK indicated that 45% of m f s had some defects within the first year and that dl roofs e x p i a c e d l& a h 20 years (see Figme 4)

W a e n c e

81.

figure 3 NRCA ~tahstics indicating that roof problem

occur

eady (62% in the h t year, 99% in the first 10 yan).

Statistics on roofs constructed

in

e a s m Canada in 1958 [Reference are &eresting when compand to those of twhyls rmfis. Over the 20 year periwl

from

1958 ta 1978 d y 17% of these

I o o f s h a d ~ a l l W i t h i n t h e ~ l O y e a r s o f ~ . ~ ~ ~ ~ ~ o a :

r ' New rather than remf a p p l h h n s

Egure 4 Statistics fmm

the

T3- Rmmch EstaWshmnt (UK) for buil-up m f s show that 45% aF the mfs had problems within the fmt year and 100% le&d after 20 yews.

Satisfadory BE Defedh H Failed

1-5 yr. 5-1 0 yr. 10-15 yr. 15-28 y. Over 20 yr.

Age of F b f s

HASTORY OF CHANGES IN ROOFING

~ ~ t h e ~ W o f t h e m ~ r o o f a p p h t i m m e t h o d s c h a n g e d b e c a n s e o f t h e i n ~ c r f m w : ~ e q u i ~ b u t d x e d e s i g n a n d ~ i n l o w SlapemdngchangedIlttle.

The nlai0ai.t~ of low-sloped roofs cons- in the 1950s were 0ne.oftwo types. wood&&

2pliesofnaiEedfelt;

3-ply felt and pitch built up roof =bran9

These t w ~ systems a~c~mted

for

q p m h m d y 40% and

204,

m p a h d y , of low-slope roofs

i n e a s ~ ~ W d ~ a c c ~ f o r ~ y 5 5 % 0 f r o o f d e c k s i n e a s t e r n Cads, with

32%

concrete, 3% metal and 8% others. Wood decb wauld likely h e

k e n

m

m o r e p r e v a l e n t i n ~ ~ c a n a d a

TheaverageI.oofshineasternCanadam 1958was r r c l y ~ m ' . ~ t e d d e c k h a d j u s t been intdnced into the madst roofs over steel deck were twice the average size.

Major changes occlnred

in

the s6cond half of the anmy- Initially at last, none of these changes a p p r to have

had

a positive efikct on roof longevity:

ca 1955 RdZM steel roof deck was inlroduced and very Wkly beg= to replace wood and concrete. Being l i m g h t

and

strong it could span widely spaced srrppwts and was

v e r y e c o n o m i c a l , ~ ~ n e x t ~ y e a r s m f s i z e s ~ I & d ~ a c c ~ ~ l ~ l t e d f a r a b o ~ t

70% of new non-residential low-slop roof dech].

Some

dhdvamgt!s of steel mf deck are:

-

tiempaatme induced expansion and ccmtmd011;

-

@ cooling of hot asphalt adhive in ml w e ,

* *

Tbede was pwr mqwhihq b e e n the highly f l m i SEA deck and built-up r o a f i n g ~ ' ~ 3 s , which kcmmrigid and brittle incold weather.

1960's

New single-ply membraoes were inmdr~ced inm,

Canada

With

very

few exc- thesedidmtpedamwell and* wereremovedfm~~the M a n m k e t .

Glass felt W-up &g was h o d m d in#, Canada. Major splitting pbIems in c o d w ~ ~ ~ o fstmmgthuftheearlyglassfiets. t h e ~ 1970's he OPEC oil 1972 M to

in-

~ X X K Y i i ~

thamat

Lighnmight plastic immMo11 foams k a m e mwe popular. TI& r e s M in

less

robust m d m o r e b l i s t e r p n e r o o f s . ~ e i $ h t f ~ a e ~ y 3 % s d i d d 9 7 % gas,

so

they have law strength, and all lightweight foams have M e air pmmabd@ which ~ i t ~ i e r t o entrapmDi~hae Ptadothergasesdufhgroof application.

Poor

adhesion M w a m sbme plastic

fm ~ ~ ~ ~ M o I I s

and

asphalt caused s i m

p r O b ~ ~ d i d ~ ~ t y b f m f o a r n i n d ~ ~ ~ . T h e ~ o f a ~ ~ ~ f o m ~ a n d t b e m c t h g ~ w a s i n ~ c e d t o ~ e

manyofthesepmb1ems.

I n ditmhkm kvds resulted in higher condmdun pomtials and the need for careful^^ tEl co~ltinuous a i r - v a p z -

Two-ply m m k 40 coated f d t

~~

wme intmdud. the perfmations of mrmber 15 felts (or glass felts) these COW felts were more prone to bUem Less hot asphalt was used dmhg application, d m wjnter the thin layeas of hot aqhdt w m rapidly -led by the thicker sheets. The Zply mmbm 40 cowfelt membrane d i d m p f m n w l a n d w a s w i . t M r a w n ~ t h e ~

1980's

By

1980 a second wave of new madmum had begun to establish itself in the Caaadian marketplace. Some

of

these membmm bronght about radically merent methods of attachment - such as b s e l y hid mcihg systems that were divorced fmm

the smctural deck. US statistics show that new membrane matmiah have had more than their share of prob1ems Ipeference 31.

MakeriaI

a

"Old" Built-up m h g 0.89

"New" M&ed bitumen "New" EPDM

"New"

W C

In addition to the above changes; year-round constnrcticm, loss of W e d labur and a "never mind the quaby, look at

the

prim? attitude has negatively impacted

the

quality of roofs. It is impossible tn idenfify the impact of each of hese f a c t o r s ' ~ ~ y , as they operate in concert. The pace and style crf bddhg m North M c a has led to a higher pacentage of latge area lightweight rwfs compared to Eumpe. A

UK

Bzrilding Research Establishment study indicates that lightweight TOO& might cost as much

as

s2x times mare to maintain compared to havyweight

roofs mference 91. This might acwm for some

of

the

difference

in roof life eqemmies b e m n Empe and North

America.

Climatic dBerences and trade apprentimship schemes are

also sigdhnt differences.

For a &tist, the last 30 years of m b g has been a Eascinating study is &chn010gy. Owners of

mismaut mfs may have had less philosophical auhdes. RE-ROOFING CONSIDERAI'IONS

The

prime function

of

a roof

is

to keep warm out of the hddhg. When a roof leaks it

is

h p m n t to understand what c a d the leak. A leak cased by an abn& event such as an antenna f d h g and puncturing a roof mendmane, does not usually q u i r e actians other h n

n@ring the punchlre and

htm

the anhenna However numerous persistent leaks are often a sign of mare e o n s problems.

While the function of a roof Is to keep water out of a building, the longevity of a mf is hrgcly dependeat upon it keeping water out of h t f . Water

is

the cause of degmdatbn of building envelopes and is especiany trne for roofs. Water within a flat roof

is

usually a prime cause of membrane

weakenin&

m m b m e k t e i n g , M o n damage., i n m e a d h a t loss, and degradation of rosf decks (sp-g of concrete, rotting of wood and d o n

of

metal). Moisture can also play a majar role in mbrane ridging, m a n h e splitting, surface m i o n and poor adhesion.

Sections 1 to 3 contain -datkms in the fodm of W s and lhnrtsw. The text in i f a h explains siome of the rasmhg behind these M o l l s . Not

all

nxmnmendaii0115 will

apply to all rmh or to all situations, but the f b m t &offers clariy.

I. Before

Deciding to

Re-roof

donot re-rdifanrmaZmxintenanceand~costsdoaot

a c e d 5% of thecost of a

new

roof, and ifminm roof leaks are tderabk

At 5% or b&w, it m&s ecomu'c seme to ltuu*ntuin the rmJ M a g n t e m e costs for

,good

ru@r me gpiculiy I to 5% @&ding on size and &w cusrs. Corn can be higher

in aceptionalye~vs, e.g. w b n r eme r e s u $ d .

Do

not entirely replace @ roofs. Spread &e work oat, m e area now,

one a m

next

Y=v=

This

tcsually m*nimiza disnptiom of qer&m and evens OW cashJhv. If

dm

pruvk&s

a good m q to assess w k t b the re-rddfing w s timely and w check w k t k xhe re-

r w n g

scheduk for other seciiuiw SW be

&&.

Do

rigidly ensare that inspections and rce of the roof are carried out each @ng

d m .

The

roof is OW of sight and more visibk items will take prme&me ti&= roof muintenace is rig* ensured. Simple dembg

of&&,

r e d k i n g flashings, etc. can

prevent nqjorjkwe problems. The spring h p m t i o n c a t c h p r o b h k t

b e

arisen

through & winter, and the fail inspecdon provides the oppommiry 10

atmi

to the roof

wore

winrer ~11-RP (repairs in winter me ~ c t d t ) .

Dt, prepare a mfreplacmxmt plan when maintenmw and repair costs exceed 6% a year.

An odd p u with mintmame und repdr cost;s gr- than 6% m*g& be qlakabk.

If

such expenditures am

m&

every yem, the rmf

L

new the end

of

i f s us@ Zfe- 2. After Deciding to

Re-roof

T k

r&ng *try Jms its sbre qf&@Ie k s i g m m and contmctom.

Do

obtain a list of their recent projects and

obtain

refisenax as to their quality

of

work.

A

sperlt mearcking the reputmiom

of

&signem und coniraetors viu p m

projects is well spent. A ptwr M g n or poor q p Z W o n r y p k d l ~ ilpcteases m~1~lnteltmcce

a d rep& c;osrs

a d

&cmuws the us@ lve of

a

raqfby sfacmr of nub.

The

combindm ufpoor &ign &poor qpIi&&rt can

r&

in a dimstrow roM-

3.

Do

not aummtidly take the Iowest bid.

Lowest

I M k s with good refkrams are

e

k

-As one qmlity roofing contractor

said,

W e on@ gef job w h & made a nristake (in

mimuti&." M i d k s s acceptmice

sf

tk bwest cust bid is a recipe for dis-. Ewopems mqy be snuzmr, in mmyjmis&&m they n#mt tkhigh and low bidr h$ore making t k k sekcri01~.

4. Do q l y with the hildhg code, n z m m d e d good m h g practice, and any wkty

and insm;ance requknmk

Cmpliance with the butIUMng code

is

a k g d rquimmnt, as is scgPety. I ~ m s may m e

prerppbm

if

tkk r w m - me nut met, and good rmfi r%sultfiom gobd r o w

p m * c e . The building code and rec- g d r-rtg p m d t x [eg. R@eremm

1 O , l l J we fowki on yams of qmience mrd tqpmh?. T k r e

am

peapk w b b&ve they kmw

h

~

wtd&

,

tkir co@&nce f a r m & their cunptettce.

W&

re-mqL!~tg, o p p d fo

new b

au'wthe , o l y ~ e r has c o r n 2 uver rk room schtduk.

Suweys

of

r@ng probIem show that half of t k p r o b b s t k t

arise

with roofing

me

m u t u b l e fo mrkmmhip [q. ReJwenm 221. Roujing in N o Yk u g h ~ ~Miach only

~~

the p r o k

Succes$ul

applietton of ro- in Carsadicur ~1-~IEKS is

~ d t , a n d s ~ r l a v m & h t ~ ~ .

If

there have been en+el~~~~ve I&- or con&nsation witkin t k old rmJ evdume the deck

for @ling, rutting or corrosibn. Rqm-7 or rep- as rrecessrny.

Do e n m e amtbuity of the air-mpar retarder*

Pay pamicub memhmhon to the roofwd1 c o ~ c f i o n of a i r - v p w retarclers. With loosely

laid single-ply d r - o w steel dmk,

$k

air-mpow retmh- com*ntaz*ty may be

critical ro lrvoid wind upl@ qftk membrane-

Do

ensure that the air-rapom -,

thermal

insubion, fihboard overlay and the mofmgmemhmearedattachedto eachotherandkdysecmdsecllred the stmmd

d e c k ( Z m l e s s ~ s y s t e m i s l o 0 s e l y Z a i d a n d ~ ~ .

Lack

of amhaem i s s m n d only m m b e as

a

pria;me c m e

of

roofing p m b h .

BitumeJe roofing mmbmnes b d d up t ~ iHtwnaI stresses ~ that cnn r d t ~ d

in flashings k i n g p d d from roof edga, intmpb sl&p~rge, m d mmbmne stuinbge, ridging and splitting- M d mm e s must be traqfmred though throof system to

$he snwhvul &ck,

and

~ sm w n ~is requid lfor this to mar.

10. Do b e l o p and dam a roof mrmag.ement plan &e. plan and ensnre that r o d m a h m a n c e i s ~ ) .

A pr-Q &IhW d a m e d ruuf ~ ~ ~ p

can

IW I G a the nw@ ive of

a rod. I&z@catiart of art W mah&mme pmonI even

if

dl me hne by

m i & conwuctofsI d l i s h e s a "point nmn", n b-et mtd the m w d s apectafiom- Dmebp the p h in mqjwdon with the &&d roofing comucmr becawe it is u good

0 p p 0 ~ * i t y rn wain ~ p k h l t ~ ~ e p ~ .

12.

Do

insist that waumty holders p d p a t e in one of &e semi-amnral m f * e

Warranty b a r s h e a vested immsi in

tk

goalp&omame of the roof and s b d d

advise the ontlter IjC repaits are - M p p r o p d or w u U void their warranty. Temwurk shouldnutersdtkmht@q&r&r@isWa

3. For Re-cover

Remove many d meus of ruqfdom to the &c;R, e p i u l l y in areas where wnm en^

k s omtwtd.

If

m y cumpmm of the m gs y a m (imlwiing tk

&&I

is found rn be

mound, increase the d rof samples until you are co@&nt that dl w o u n d mw

W e

been fd. Repair or r e p k e m u t e M as necessary.

Flashings

are

a

lnojor source for warn enby arad t h y g e d b d m e ~ r u t e f m r t h themembrane. The rkr'cRnars inmeare

of

rte

re-cmwed roofing system requires m wrmd &rs at rmf edges to accmww&e the nav m u m i d s and to s u p p ~

w u n t e ~ h h g s JR@krmce 151.

15.

Do

not &me the new m gmmibam to the old m & g mmbme, Always proviide a

separation layer.

A fibrous b a d is prt$md a ventiw k s e sheet. I l l ~ ~ a r e d i m w o n should be

comid~ed* Mechdcal fastening

of

the

new

i d a t i o n s andlor the fibrous

layer

is

pn$eW

as

it b mr re& on u d h a b n of thold roofing s y s m . Slicing tkold

membrane p n m m it =ring mb

a

s e c o d q wpow r m & r -

~ ~ t h a t 7 5 % a f a l l r o o f ~ a r i s e ~ r a o f m d e q u i p ~ partidar@ amdendon fmnHVdC units and badly mdkeddpenemiom

~ ~ g ~ ~ i s ~ ~ ~ ~ ~ ~ ~ c e d ~ g c o n t t a c t r a ~

crews are especially v & a b when it .tto t o g lab Non-desrmtible analysis such

as

h l h - d lknmgraphy, capacitance meters, nenmn a b s q t h gauges, or

-

w

dewdunmethods

can k

employed.

h ~ ~ r ~ a r e u s e f n l t o ~ t h e ~ a r e a o f r o o f ~ a n d t o v ~ t h a t r h a i s a roof leak as

opposed

to adensation

or

plumbing pPobI=. Roof lmb over -4 steel deck

can be misleading because the deck flutes act as gumn and water can flow a considerable disnrncebefcrreentakgthe~.Atleastitisa 'I-

I s e m c h d a f e w ~ h o l e s can Usuany help bxte w brhe water is penetrabg the air-vqmm remder.

B m

IN

BUILT-UP RddFS

T I d s ~ t h e m o s t c o m m o n ~ w i r h h o t a p p ~ ~ t - n p m g m m . It apprsthaxas lung as thme has

k

built-up roohng mernhranes there have h e n roof bWm. Fornmately the causes a n d c l m e s o f r o o f ~ b ~ arewellandersbood.

Analysis of over 10,000 buibup

roof

samples has shown that blistm can only develop if initial v o i d s , o r m ~ ~ , ~ p r e s e n t ~ ~ - ~ ~ w n c e l 6 J .

It has k e n demonstrated that a perfect void-free rwf m o t be laid even unda ideal mnditions 1 7 - Voids can result from skips m binmen ampping, entrapped debis, =led felts,

I unevenmbmam,andfram ~ m i s t m ~ t h e m f m h i n t h e ~ t o e n t r a p p e d ~ s

and bitumen bubbling

B l h n rarely develop if the total area of voids per intebply is less than 5% of &e hstalled are^^ Theoretically mi& less than 19 mm .in length will not grow into Histers [Rehence 151. O w e

~ g r o w , ~ ~ w i l l g r o w r a p i d l y ~ e ~ ~ e c a u S i n g t h e b l i s t e r m g r a w i n ~ s ~ ~ volume

(

e

s q u a d ) wherm bbnd strength at the p i p h a y CFF the b l h r in- with

chcnmference (diatne&r to the power of one).

B ~ g ~ w ~ p o c ~ d a i r a a d ~ t r a p p e d ~ n t h e p k o f t h e m e m ~ a r the m m h n e and subsmte, e mm the sudden heat of the sun and displace tbe mmhme to

farm a small blister. T%e bkm will d y be farmed when the marmiah have Iow p m d h y ;

. .

~ t h e s e ~ s ~ ~ h rheat noftbe t hmcanTisetaa qukklyfortqpd e air and water vapom to eswlpe. Ressures will then develop

in

the air puckets and dis can cause a

d i s p ~ t a n d ~ o f t h e r o o f ~ p r a d u c i n g a n ~ i n t h e ~ o f ~ ~

mm-.

~~~n about Mismsis that they arept&dy:xxdd Ifthis were the case b&ms

w o u l d ~ g r o w ~ r h e ~ ~ ' d i c r a t e d b y ~ g a s ~ ~ ~ l ~ t i n ~ e b l i s m d t h c ~ smfacemnpemmeofthemof, In apdedyclosed andelastic symmavbidwithinamufwill

grow due to h e e x p u s h of airand/orwa~~wpwbyday, h t i t d s a b s i d e to its o r i g i d

dimensions st mghL

Built-up mfmg mmhams are not perfectly elastic, they expand d ywhen ttrey are warm but

~ s t i f f ~ I . e s i s t ~ t a ~ ~ ~ w h e n t h e y ~ c o b l d A n y ~ t Mmwimof themeoabmewillcmateavacuumwi~theMistaaud airwillfinditswayinm

t h e e n e l a s e d ~ ~ u g h ~ c r a c k s j n b i t u m e n ~ g s , a I q ~ e ~ , a r ~

the s a , b ~ t o ~ ~ t h e o r i g i n a l ~ k e t ofair. me blisterisnow d i f l y ~ i n s i m , tapped up with

p s m e and

m d y to start auother cycle of develqmmt when the mzn a

Egare 5 R w f ~ ~ m b blisters.

Pocket of trapped

air and moisture Pocket of

trapped oir

and moisture

Rapid expansion o f Vapour pressure rises trapped air and too fasf for escape moisture forms through dense dec small blister

NIGHT

Pclrtial vacuum af night draws additional air and water vapour into blister from deck

Padial vacuum at night draws additional air and water vupour through micro cracks

Blisters gmw when:

I, the volume of air sucked into them at night exm& the volume of air h e d out of thw by day,

An haeased ocmmam of blism between cellular foam hdatim and roof m m h a n a was iniihly thought to be due to gases escaping the & of thtxe hadahm. Although there is fitde evidence fa this, it is clear that the h n p ~ m ~ I e mtmc of cellular foam iasuhions cm ~ U ~ d a e t c , t h e i r M ~ t 6 m t ~ M * g ; a n d * m f applicaticm.The use of a

-us

covehard ( w d g h ~

h

or pZite

board)

over cellular insulations

is

recrrmmeraded m d a c e the ocammce

af

blisbers h built-up roofs Befhmces 19,

201.

B ~ g o f f e l t s a s ~ ~ l a i d i n t o h ~ ~ t i s ~ t o ~ i n ~ e c o n t a c t ~ ~ Ebbs a d between the ~ I B and the snbsttate, thereby reducing the size and m m k of voids built

into tbe rwf.

S 7 E L ROOF DECK CORROSION

W o n of steel-f d e c k i s a t o j i c a l p r o b h i n k ~ i n d u s t z y . 7lme are some stmightfbmard aspects to steel roof deck c d o n and ;~ame not so -strai-

I f w a m & s m e n ~ a d ~ ~ & ~ k ~ k b S t ~ y . S ~ r o o f ~ k

~ O X dues X not wcm without water. If water enters a loof dmugh membrane leaks or

exinme c o w o n then,

trased

on

labarataay

tess,

a d k k s s Zoss of 0.02 to 0.10 mm ptz

y e a t c a n b e ~ C i i v ; e a t h a t ~ u s e d Z F 0 7 5 ~ d e c k i s 0 . 7 6 m m ~ ~ k , t h i s c c m s p n d s t o a 2 ~ 13%lossofdeckthiclamessperyear.

F ~ ~ n c e ~ ~ s ~ d e c k ~ ~ ~ i s m a r e c o m p h c a i d , andthatroofsthat have -cant and m q a k d leaks can exhibit pin-holed S& deck kt abont

3

years.

Two

US

mnufachmn and me of three ~snadisn rmnufadurmd Plxmok foam insuhiun have made to theindustry which

warn

of thepQkmtial for a c o e ~ ~ curmsim of s l d roof deck. The armomcement In ranadsl is limited ho nwfk which have beexl installed with Domtar phenolic h s u h h n witboat vaponr

retarders over

steel nmf deck m p e a n matlufaamm of

p h e m i c ~ h a v e ~ n o s n c h m w ~

The psmce o f p h d c foam inadatinn has no accelerating .dkct u pcorrosion in a dry roof.

A n o ~ ~ ~ w h ~ p h e n o l i c ~ ~ ~ h o w e n o ~ a p o n ~ e ~ o f g a l v ~ steel deck d m

is

when there are massive m f l e a k G m h ~ and Eumpean rmf decks are

the s i t m t b

is

diffmm~in the

US.

Solongasvapwzrretamlashavebeeninsralledaadmf leaks arerepaidin a timelyfahion, it

a p ~ t h a t ~ i s ~ d ~ a f c ~ o n ~ a n y p a r t i c u l a r ~ t y l p e .

~ d ~ ~ t h a t a l l ~ o f ~ c a n ~ d w o f ~ r o o f d e c k

'Ihebest~ya,pnv~nramekraredcmsionofsteelroofd~istoplrevent wamfbmenking the mf.

"Candata Building Statistics", National -8 Swthams Cmmwtion Infcnmation Smites, 1969 on&.

Useful summak of t b e ~ e data are presented

in

"Canadata A n n d & e o n Forecasts" d the United Nations "Cwsmction Statistics YmrhoY-

2. Kane, K, "How was 1995?" R o f d m l Rding Magazine,

US.

National R 6 g ~ m c t u r s A s s m a m & * * March 1996.

" " F i x e d ~ F 1 0 ~ ~ a n d S t o c k s - M e ~ 1 0 g ~ ~ u ~ - N ~ W e a l t h a n d Capital Stock Selecticm" Investment and QIM S W Division, Statistics Canada, 1990.

CSA S478-95,

"m

. .

in in

B

-

Strnctures @esignjn, Stadads hsmiation, December 1995,

Booth,

R

3, 'Zife &tory of Built-up Rmfs Bonded by DomEar in 1958", Domtar Reseanh Me-- July 1979.

W

dmmmt is not openly maihble. Excerpts p v i d e d with p m i s i o n of

h m r

h.]

Zdanuwh, A., IFht Roof

Pafonnanoe",

hceaihgs of Third Confixelm on Bidding Science a d Techaology, Gumdim S* far Civil Enghexhg, November 1985.

"Asphalt

and

hilt-up felt m-: dumbility'', UK Building

Research

Staim Digest 144, Angust 1972.

Wolmes, R el al, nMabtenance GUS&

of

flat roofst', Bddhg Fkmd~ Es-t,

U K ,

C m a t paper448 1,1981.

"Roofing Specikahm", Canadian Rwfing Associatun, Updated a n n a y .

'NRCA -g

and

waproofing Manual, Folrrth Edition", National R e g Conaactlws

,

-

A

U.S.,

1995.

'Manual for

Trlspection

d MaMmance

of

Built-Up

and

Mdified Bimmm R o d

Sysoems: A Guide For Bddhlg Owners", Mhdt R d g

~~

A ~ 8e m

National R&g Conmctm

Associatiw,

1996,

'Manual of Roof

~~,

Maintenance, and Emagwcy Repair

for

Ekthg SmgbPIy R m h g Sys~ems", ShgbpIy

R d g

Insritnte & N a t i d Roofing &nmmrs

15. GxBm, C.W. &

m,

R.L.,

'The Manual

of

low-5lo]pe Roof Systemsn, Third E d i t h , -w-Hill, 19%.

16. Dwight, F. & J d g ~ , P.E., '?kve&lg M i s d bdt-UP w ~ s " , Second

In

-

symposinm

on

Roofii and Roofing, London Society

of

the Chemical Indusuy (1981). 17. M e n , W.C, "The P a f a Rmf:

Can

It Be Buitt'?'', R o o k g '87, NRCA, (1987).

18. Horhonen, C dk Charest,

B.,

'Rod Blisters, Can= mi k",

US

Axmy Corps of Engineers, Cold Regi~xls R-h & En-g L a m ,

R

w

95-19, July (1995). 19. 'WRCA S m e n t w P o l y i s o q a u ~ , hlytmthane and P k & c Foam Rmf