READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright
Vous avez des questions? Nous pouvons vous aider. Pour communiquer directement avec un auteur, consultez la première page de la revue dans laquelle son article a été publié afin de trouver ses coordonnées. Si vous n’arrivez pas à les repérer, communiquez avec nous à PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca.
Questions? Contact the NRC Publications Archive team at
PublicationsArchive-ArchivesPublications@nrc-cnrc.gc.ca. If you wish to email the authors directly, please see the first page of the publication for their contact information.
NRC Publications Archive
Archives des publications du CNRC
This publication could be one of several versions: author’s original, accepted manuscript or the publisher’s version. / La version de cette publication peut être l’une des suivantes : la version prépublication de l’auteur, la version acceptée du manuscrit ou la version de l’éditeur.
Access and use of this website and the material on it are subject to the Terms and Conditions set forth at
Moisture attack on insulations in protected membrane roofing
Hedlin, C. P.
https://publications-cnrc.canada.ca/fra/droits
L’accès à ce site Web et l’utilisation de son contenu sont assujettis aux conditions présentées dans le site
LISEZ CES CONDITIONS ATTENTIVEMENT AVANT D’UTILISER CE SITE WEB.
NRC Publications Record / Notice d'Archives des publications de CNRC:
https://nrc-publications.canada.ca/eng/view/object/?id=b8a48ace-1ee2-4325-9790-19017a2c2e60
https://publications-cnrc.canada.ca/fra/voir/objet/?id=b8a48ace-1ee2-4325-9790-19017a2c2e60
1 - H e d l i n
MOISTURE ATTACK ON INSULATIONS I?;
P R O T E C T E D MEMBRAXE ROOFIKG C h a r l e s P. Hedlln D i v i s i o n of Building R e s e a r c h , P r a l r l e R e g l o n a l S t a t l o n N a t i o n a l R e s e a r c h Councll of C a n a d a . S a s k a t o o n , S a s k a t c h e w a n , S 7 K O J Y 9 ABSTRACT T h e r ma1 i n s u l a t i o n i n p r o t e c t e d m e m b r a n e r o o f i n g m a y be e x p o s e d t o r a i n and s n o w . Out- d o o r e x p e r i m e n t s w i t h r o o f i n g i n s u l a t i o n s , In- cluding s o m e p o l y s t y r e n e s , p o l y u r e t h a n e s , wood f i b r e , g l a s s f i b r e and p e r l i t e - f i b r e , con- f i r m t h e s e v e r i t y of the p r o b l e m of m o i s t u r e a t t a c k but i n d i c a t e t h a t p r o t e c t i n g i n s u l a t i o n s by s u r f a c e s e a l i n g and p r o v i d i n g f o r m o i s t u r e e s c a p e by e v a p o r a t i o n and d r a i n a g e m a y keep m o i s t u r e contents of e v e n s o m e p o r o u s in- s u l a t i o n s a t low l e v d l s . I1 a r r i v e q u e l ' i s o l a t i o n t h e r m i q u e d e s t o i t s 'a m e m b r a n e p r o t 6 g b e s o i t exposite 'a l a pluie e t 9. l a neige. D e s e x p 6 r i e n c e s e n p l e i n a i r s u r d e s i s o l a n t s pour t o i t s , y c o m p r i s d e s poly- s t y r 8 n e s , d e s p o l y u r b t h a n e s , d e l a f i b r e d e b o i s , d e l a f i b r e d e v e r r e e t de l a f i b r e d e p e r l i t e c o n f i r m e n t l a difficult6 d u probl'eme d e l l h u m i d i t b , tout e n indiquant q u e l a p r o - t e c t i o n d e s i s o l a n t s p a r s c e l l e m e n t s u p e r - f i c i e l , l l b c h a p p e m e n t d e l l h u m i d i t b p a r Bvapo- r a t i o n e t l e d r a i n a g e peuvent a s s u r e r une f a i b l e t e n e u r e n h u m i d i t 6 mSme de c e r t a i n s i s o l a n t s poreux.
2
-
Hedlin IntroductionIn protected m e m b r a n e roofing s y s t e m s , the insulation i s located above the m a i n i m p e r m e a b l e m e m b r a n e . E a c h of t h e s e c o m - ponents p e r f o r m s i t s u s u a l functions but i n a d i f f e r e n t e n v i r o n - ment than i s the c a s e i n conventional f l a t roofing s y s t e m s . F o r m o s t f i e l d applications i n Canada, few if any s p e c i a l mea- s u r e s a r e provided to p r o t e c t insulation i n p r o t e c t e d m e m b r a n e roofing a g a i n s t p r e c i p i t a t i o n . The insulation is placed on the m e m b r a n e and e i t h e r bonded to it o r left unbonded. It i s covered with g r a v e l o r paving s t o n e s to i n t e r c e p t s o l a r r a d i a t i o n , to hold the insulation i n place and, i n s o m e c a s e s , to s e r v e a s a traffic
I s u r f a c e . S o m e of the w a t e r f r o m r a i n o r melting snow p e r c o l a t e s
I down to the m e m b r a n e w h e r e t h e r e may o r may not be a slope t o
p r o m o t e i t s flow to d r a i n s . Under t h e s e conditions, only those insulations t h a t a r e highly r e s i s t a n t t o w a t e r p e n e t r a t i o n can r e m a i n d r y .
T h i s a r r a n g e m e n t l e a v e s t h e insulation o p e n to e n t r y of m o i s t u r e through the top and bottom s u r f a c e s and the edges. Any water that f a l l s o n the top s u r f a c e may p e n e t r a t e the i n s u l a t i o n o r e v a p o r a t e , if conditions p e r m i t , c a u s i n g l i t t l e or no d a m a g e . Water m a y stand i n t h e hutt joints, F o r insulations w i t h fibre ends a t the edges this r e p r e s e n t s a p a r t i c u l a r l y v u l n e r a b l e a r e a . M o i s t u r e t h a t finds i t s way between t h e insulation and t h e mem- b r a n e i s l a r g e l y i s o l a t e d f r o m e v a p o r a t i v e and d r a i n a g e f o r c e s if the r o o f i s flat. I t i s likely to r e m a i n t h e r e f o r a long period of t i m e , p o s s i b l y until i t is r e p l e n i s h e d b y f u r t h e r precipitation. (Fig. 1).
3 - Hedlin 8 1
,
I , ( I ) I , T O ' 1 1' .
, 1 1 1 1 ! , I , I , I ' t l ' 1 I l l 1 # I,
I D R A I N S 1 # I , , , TOP C O V E R / i N s u L A T I o Nd
--MEMBRANE \ D E C K FIG. 1 Water flow in a p r o t e c t e d m e m b r a n e roofing s y s t e mT h e m o i s t u r e a t the insulation-membrane i n t e r f a c e constitutes a particularly s e r i o u s t h r e a t not only b e c a u s e of the prolonged ex- posure but because the t e m p e r a t u r e a t the bottom of the insula- tion i s usually higher than a t its top s u r f a c e . This s e t s up a vapour p r e s s u r e gradient which d r i v e s m o i s t u r e into the insula- tion and toward the colder s u r f a c e . If the top s u r f a c e i s open, s o m e of it may condense i n the insulation and some will e s c a p e to the outside. If the top s u r f a c e i s c o v e r e d s o that e s c a p e is inhibited, m o r e i n t e r n a l condensation will o c c u r with a n i n c r e a s e d probability that the insulation will become wet.
A v a r i e t y of protective m e a s l i r e s can be applied. T h e i r efficacy will depend on t h e c l i m a t e and on the n a t u r e of the insulation. T h e s e m e a s u r e s include s e a l i n g the insulation s u r f a c e s t h a t a r e most vulnerable to m o i s t u r e e n t r y , sloping the deck, a r r a n g e - m e n t s to f a c i l i t a t e u n d e r - s i d e and top-side drainage, and the use of top-side ventilation to aid escape of m o i s t u r e f r o m the insula- tion.
E x p e r i m e n t a l Work
Studies have been c a r r i e d out a t the P r a i r i e Regional S t a t i o n of the Division of Building R e s e a r c h a t Saskatoon with a v a r i e t y of insulations on protected m e m b r a n e r o o f s . In 1966, r i g i d f o r m s
4
-
Hedlinof g l a s s f i b r e , ( a b b r e v i a t e d G F in T a b l e I ) , wood f i b r e ( W F ) , u r e t h a n e s ( P U ) , e x t r u d e d p o l y s t y r e n e ( E P ) , bead p o l y s t y r e n e ( B P ) , c e l l u l a r g l a s s ( C G ) , polyvinyl c h l o r i d e ( P V C ) , c o r k ( C K ) and p e r l i t e - f i b r e ( P - F ) , w e r e placed on t h e roof of a n outdoor e x p e r i m e n t a l building. D e c k s l o p e w a s nominally 1 i n 48. They w e r e s u p p o r t e d on a 0 . 0 2 5 - m - t h i c k l a y e r of pea g r a v e l ( O G ) f o r d r a i n a g e , o r r e s t e d d i r e c t l y on the r o o f i n g m e m b r a n e ( O D ) . T o p
2
c o v e r s i n c l u d e d 0 . 6 m x 0. 0 5 m t h i c k c o n c r e t e p a v i n g s t o n e s r e s t i n g on the top s u r f a c e s of the i n s u l a t i o n s (SD). S a m p l e s of s o m e of t h e i n s u l a t i o n s w e r e weighed p e r i o d i c a l l y d u r i n g a 3 - y e a r p e r i o d . C e l l u l a r g l a s s and two p o l y s t y r e n e s w e r e e x p o s e d for up to s e v e n y e a r s . Some r e p e a t t e s t s w e r e begun w i t h p o l y s t y r e n e s i n 1971.
I n 1969 e x p e r i m e n t s w e r e b e g u n w i t h f o u r i n s u l a t i o n s and com- b i n a t i o n s of s e v e r a l p r o t e c t i v e d e s i g n f e a t u r e s . G l a s s f i b r e , wood f i b r e , p e r l i t e - f i b r e and a p o l y u r e t h a n e w e r e used. The
I p u r p o s e w a s t o study t h e e f f e c t i v e n e s s of s e a l i n g b o t t o m and edge I s u r f a c e s , t h e u s e of t o p - s i d e v e n t i l a t i o n a n d the e f f e c t i v e n e s s of a g r a v e l d r a i n a g e l a y e r i n p r e v e n t i n g m o i s t u r e a c c u m u l a t i o n in the i n s u l a t i o n s . 2 2 S a m p l e s 0. 15 m x 0 . 0 5 m t h i c k w e r e c u t f r o m 0. 6 - m s p e c i m e n s of e a c h i n s u l a t i o n . T h e b o t t o m and e d g e s u r f a c e s of s o m e of both s i z e s w e r e c o v e r e d w i t h coated b a s e s h e e t a d h e r e d with hot a s p h a l t (S). T h e top s u r f a c e w a s l e f t u n s e a l e d in a l l c a s e s . A l s o , s p e c i m e n s w i t h no s e a l e d e d g e s w e r e u s e d a s c h e c k s ( U S ) . Some w e r e p l a c e d o n a g r a v e l d r a i n a g e l a y e r a n d o t h e r s on t h e mem- b r a n e . T o p c o v e r s c o n s i s t e d of paving s t o n e s s u p p o r t e d about 0 . 0 2 m a b o v e the i n s u l a t i o n s u r f a c e by s t r i p s of wood to provide v e n t i l a t i o n (SU) o r a t o p c o v e r of 0 . 0 2 - m - d i a m e t e r g r a v e l was used
(UG)
( F i g . 2).5
-
HedlinFIG. 2
Design f e a t u r e s used i n tests: SD
-
stone on insulation s u r f a c e ; SU-
stone up (ventilated); UG-
under g r a v e l ;S
-
s e a l e d on bottom edges; U S-
unsealed; OD-
on membrane; OG - on gravel d r a i n a g e l a y e r .The 0. 15-mL specimens w e r e usually weighed three t i m e s a year
-
in s p r i n g , s u m m e r and f a l l-
to d e t e r m i n e whether they had gained moisture. (Annual precipitation f o r the a r e a a v e r a g e s2
0. 35 m . ) The 0 . 6 - m s p e c i m e n s w e r e a l s o weighed but l e s s frequently. On a v e r a g e , they reached m o i s t u r e contents about 50% lower than their s m a l l e r counterparts. This i s probably due, a t l e a s t in p a r t , to their s m a l l e r a r e a / v o l u m e ratio.
R e s u l t s and D i s c u s s i o n
Average and maximum m o i s t u r e contents f o r most of the tests a r e given in T a b l e I. S e v e r a l s e t s of r e s u l t s were plotted to i l l u s t r a t e continuing o r .short,-term t r e n d s o r to show the effect of different t r e a t m e n t s . P o i n t s in Fig. 3 a r e averages f o r three to six s p e c i m e n s . F i g u r e 4 i s for single 0. 15-mL s p e c i m e n s Undue e m p h a s i s should not b e given to individual r e s u l t s because, i n many c a s e s , they w e r e obtalned with single specimens and wide variations can occur d u e to local conditions on the roof. Also, r e s u l t s f o r a given g e n e r i c type should not be taken a s applicable to a l l products of that type, s i n c e formulations and manufacturing methods may significantly change the c h a r a c t e r - i s t i c s of m a t e r i a l s . The main purpose of the studies w a s to test concepts, to identify a r r a n g e m e n t s that might work and to a s c e r -
T A B L E I
A v e r a g e (A) and Maximum (M) M o i s t u r e Contents
(70
of g r o s s volume) of Insulations. P e r i o d s of E x p e r i m e n t : above double l i n e 1966-69 e x c e p t E P 1966-73and s o m e B P 1971-73; below double line 1969-73
T r e a t m e n t CK P V C P U E P B P G F W F P-F P U S D O D U S A 1 6 11 19 2.0 Fig. 3 4 5 4 8 10 M 33 1 8 37 4 . 4 59 90 2 1 S D O C U S A 9.2 3.5 9 . 6 0 . 3 F i g . 3 12 1 8 2 . 1 M 20 6. 2 18 0 . 6 17 4 5 4 . 3 S U O G S A M U G O D S A M U G O G S A 29 1.7 0 . 4 0 . 5 M 7 7 4.0 0 . 8 0. 6
7
-
Hedlint a i n the g e n e r a l effects of the different design features both in- dividually and in combination.
FIG. 3
Moisture contents in cellular g l a s s ( C G ) and a bead-type polystyrene (BP). T e s t s
s t a r t e d in 1966,or 1971, a s indicated.
Moisture gains varied widely depending on the type of insulation. As expected, the open p o r e insulations r e a c h e d higher moisture contents than the closed cell types. The s e v e r i t y of the moisture s t r e s s imposed on insulations that a r e sandwiched between the membrane and paving s t o n e s is'iLlustrated by the high moisture contents r e a c h e d by many of them, including even bead-type polystyrene and cellular g l a s s . (Fig. 3)
T h e moistur'e contents of unsealed insulations resting d i r e c t l y on the m e m b r a n e exceeded that of insulations on a g r a v e l drainage
8
-
Hedlin FIG. 4 2 Moisture c o n t e n t s in 0. 1 5 - m p e r l i t e - f i b r e insulations s u b j e c t e d to d i f f e r e n t t r e a t m e n t s l a y e r . F o r a l l r e s u l t s t o g e t h e r ( r e g a r d l e s s of o t h e r t r e a t m e n t s ) the r a t i o w a s a p p r o x i m a t e l y 2 to 1. A s i m i l a r r a t i o o c c u r r e d when r e s u l t s with a g r a v e l c o v e r w e r e c o m p a r e d w i t h t h o s e for paving s t o n e s r a i s e d t o p e r m i t ventilation.When g l a s s f i b r e i n s u l a t i o n w a s s e a l e d , m o i s t u r e c o n t e n t s w e r e higher t h a n when i t w a s not sealed. Apparently t h e net effect of s e a l i n g w a s t o impede outward d r a i n a g e of moisture. F o r wood f i b r e insulation, the a v e r a g e m o i s t u r e content f o r a l l unsealed p i e c e s w a s 3070 by volume; f o r a l l s e a l e d ones it w a s 1. 770. F o r
9
-
Hedlinp e r l i t e - f i b r e the corresponding r e s u l t s w e r e 14 and 0. 4%. For polyurethane sealing a p p a r e n t l y caused a reduction 1 1 , a v e r a g e m o i s t u r e content f r o m 2. 2 t o 0. 470.
Moisture gains by wood f i b r e , p e r l i t e - f i b r e and polyurethane insulations s e a l e d in this way appear to be small. H o w e v e r , it should be recognized that the m o i s t u r e is concentrated n e a r the upper s u r f a c e and this portion of the m a t e r i a l may undergo s e v e r e m o i s t u r e s t r e s s .
Conclusion
T h e s e a r r a n g e m e n t s t o p r o t e c t insulations i n protected m e m - b r a n e roofing s y s t e m s a r e b a s e d on t h e concept that w a t e r should be prevented f r o m e n t e r i n g the insulations but, in c a s e it does, a means of e s c a p e should be provided.
T h e r e s u l t s d o not give a comprehensive picture of the effect of different a r r a n g e m e n t s on m o i s t u r e movement in the roofing s y s t e m . They do provide s o m e information, however, about the r e l a t i v e ability of different d e s i g n f e a t u r e s to provide protection f o r insulations. The r e s u l t s appear t o s u p p o r t the concepts put forward in the introduction ahd to d e m o n s t r a t e , experimentally a t l e a s t , that protection can keep m o i s t u r e contents low e v e n in s o m e f a i r l y porous insulations.
F u r t h e r work is being done. T h e effect of deck s l o p e , underside fluting and top-side flashing a r e being studied. M e a s u r e m e n t s on dimensional stability and m o i s t u r e gain i n s e v e r a l s e a l e d insulations a r e being o b s e r v e d by the Division of Building Re- s e a r c h i n the wetter c l i m a t e a t Ottawa.
Acknowledgements
T h e author wishes to r e c o g n i z e the s p e c i a l contribution of D. G. Cole i n the planning a n d conduct of t h e e x p e r i m e n t a l p r o g r a m .
1 0
-
HedlinA p p r e c i a t i o n i s a l s o d u e G. 0 . H a n d e g o r d , G. K. G a r d e n , and J. T. Makohon f o r t h e i r contributions to t h i s study, T h i s paper i s a c o n t r i b u t i o n f r o m the D i v i s i o n of Building R e s e a r c h of the N a t i o n a l R e s e a r c h Council of Canada and i s published w i t h the a p p r o v a l of t h e D i r e c t o r of t h e Division,
