Effect of solar heat on moisture gains in building perimeter insulation beneath a paving-stone walkway

Publisher’s version / Version de l'éditeur:

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.

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.

Building Research Note, 1982-09

READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS WEBSITE. https://nrc-publications.canada.ca/eng/copyright

NRC Publications Archive Record / Notice des Archives des publications du CNRC : https://nrc-publications.canada.ca/eng/view/object/?id=909e72cf-a7d7-404d-b99f-8948a91f4a1a https://publications-cnrc.canada.ca/fra/voir/objet/?id=909e72cf-a7d7-404d-b99f-8948a91f4a1a

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.

For the publisher’s version, please access the DOI link below./ Pour consulter la version de l’éditeur, utilisez le lien DOI ci-dessous.

https://doi.org/10.4224/40000519

Access and use of this website and the material on it are subject to the Terms and Conditions set forth at

Effect of solar heat on moisture gains in building perimeter insulation

beneath a paving-stone walkway

BUILDING

RESEARCH

NOTE

EFFECT UF SOLAR HEAT

ON

PERDETER INSULATION EENEATH A PAVING-STONE WALKWAY

by

C'.P. Hedlin and D.G. Cole

Ottawa, September 1982

D i v i s i o n of Building Research, National Research

.--.

-EFFECT OF SOLAR HEAT ON MQISTURE GAINS IN BUILDING

PERIMETER I N S U T I O N BENEATH A PAVING-STONE WALWAY

C.P. HedLin* and D.G. Cole*

The Outdoor Test Buildiug of the P r a i r f e Regional Station,

Division of Building Research, National Research Council, was constructed at Saskatoon in 1966. The facility is u s e d i n studying the performance of building materials and experimental building systems under realistic

service conditi~ns. Included In the construction is a _{1220 mu ( 4 f t )}

w i d e walkway of 58 dtm (2 in.) concrete paving stones d i r e c t l y against the north, east and south s i d e s of the building (Figure 1).

The walkway is underlaid w i t h thermal i n s u l a t i o n , as one way of

applying perimeter I n s u l a t i o n t o the building. As _{one parL of t h e walk}

l i e s along the south side of t h e building and the other along the narth

s i d e , the df fferent exposures affect the amounts of solar heating of the walkway. This would affect water vepour pressure and the s e v e r i t y of

moisture attack on t h e insulatian. Since maisture gain affects the

thermal performance of insulation, measurements were made p e r i o d i c a l l y to

determine i t s moisture content.

At the t h e of construction, extruded polystyrene sheets 51 mm

(2 in.) t h i c k and 618 by 1220 mm (2 x 4 ft) w e r e p l a c e d d i r e c t l y under

the paving atones on the underlying sandy loam soil. In 1974 several specimens of rigid glass ffber were p u t into p l a c e so that their moisture contents emld be observed.

EXTRUDED POLYSTYRENE

The polystyrene had a d e n s i t y of 38.7 kg/m3 (2.4 l b / f t 3 ) . S a m p l e s a p p r o d m a t e l y

lQD

samples were removed and weighed p e r i o d i c a l l y , beginning in 1968. In 1973, periodic weighing of two full sheets (610 >e 1220 mm) was begun,

One of these sheets was located at the d d d l e of the south s i d e and t h e

other an the north aide at the NE corner of the _building.

Results of the p e r i o d i c weighings of polystyrene are shown i n

F i g u r e 2. Moisture contents on the north side are almost unchanged s i n c e 1973; on the east s i d e they continue t o increase and on the south s t d e

rise sharply, with l i t t l e i n d i c a t i o n that the rate of uptake is easing.

To improve the evaluation of moisture, additional 610 x 1220 mm sheets were weighed in 1978. The restilts are s h m in Figure 3 f o r

individual sheets on the north and south s i d e s of the building. Moisture content o f t e n south-s%de sheets ranged from about 5 . 5 to 10.1%. When

five of these were rewefghad in 1979, moisture content (not shown on the

graph) had increased by amounts ranging up t o 1%.

Based on the 1978 weighings, maisture contents of the east-side sheets (not s h m in graph) were 4.1 and 5.1%; on the north s i d e ,

moisture content sf the four specimens ranged from 1.8 to 2.9%.

The presence of moisture combined with temperature gradients can

produce vapour pressure gradients, which d r i v e moisture inta the

insulation through both the upper and lower surfaces. Heat flow out of t h e building produces such a temperature gradient at the bottom surface through the winter. Periodic heating of the paving stones by sunlight ~ $ 1 1 cause mi sture trapped beneath t h e stones to e n t e r the i n s u l a t i o n

through the upper surf ace.

As there is no reason to suppose that the available moisture varies from one side _{of the building} to t h e other, the difference in

insulation maisture content probably stem from the heatiag effect of the sun. On the south side of the building, the paving s t o n e s are exposed ro

d i r e c t sunlight and to radiation reflected by

the

wall. This effect: is less an the east w a l l , and much less on the north w a l l . This is illustrated in Figure 4 , which shows temperatures measured

at t h e interface between stones and insulation .on the three sides during

a sunny day in June.

Top surface m o i s t u r e gain can be reduced by ventilation above the insulation. This has

a

( 2

air c i r c u l a t i o n over the top surface of the insulation. Three others where the s t o n e s had n o t been raised were used a s controls. As s h m in Figure 5, those with no ventilation continued t o gain moisture while

those with ventilation lost moisture.

These results paralleled those obtained in simflar tests on insulation in protected membrane

roof s1

GLASS FIBER

In 1974 two polystyrene sheets were removed f r o m the south sZde

and t w o from the north s i d e ; these were replaced by r i I d glass fiber sheets 49 im (2 in.) t h i c k . with a d e n s i t y of 150 bg/mf ( 9 i b , f r 3 ) . Some

of _these had asphalt impregnated s h e e t i n g on one surface while the others

had no surface protection.

After three and a _{half years the glass fiber sheets reached}

moisture contenes ranging u p t o 7.1% by volume ( T a b l e 1). They f l u c t u a t e

This material is much more subject t o seasonal variations in moisture

cantent than the polystyrene.

Both kinds of insulation are penetrated by grass roots. In t h i s case i n d i v i d u a l roots have penetrated up t a _{200 mm o r m o r e . Root}

penetration d i d not appear to cause serious damage t o the i n s u l a t i o n .

CONCLUSIONS

Extruded polystyrene of 38.7 kg/m3 d e n s i t y placed on sail under concrete paving stones adjacent to north-, east- and south-facing walls of a building showed moisture gain over a 13year period. It was least along the north-facing wall, greater along the east-facing wall, and

highest along the south-facing wall. This is attributed to differences

in paving stone temperature and, p o s s i b l y in soil temperatures beneath

the insulation.

These temperature differences w i l l occur due to differences in solar radiation reaching the paving stones e i t h e r d i r e c t l y or by

reflection from the adjacent walls. Its effect _{on moisture gain occurs}

because the vapor pressure of rain water, trapped between the paving stone and t h e fnsulation, rises w i t h temperature. The resulting increase

fn vapor pressure gradient accelerates the accumulation of moisture in the insulation. The effect will be greatest where the solar heating is

g r e a t e s t - along the south s i d e .

A secondary effect may exllst. If the solar g a i n warms the soiL beneath the insulation, increased vapor p r e s s u r e w i l l accelerate

moisture gain through the bottom surface of the insulation. Top surface v e n t i l a t i o n causes a reduction in moisture content; observatsions have

not been carried on long enough t o determine what the f i n a l level of

maisture content will be.

Moisture contents of rigid glass fiber i n s u l a t i o n under the p a v i n g stones fluctuated, and ranged up to a rraaximum of 7 . 1 X by volume.

1, Hedfin, C.P. Moisture Content in Protected Heabrane Roof Insulations

-

b t e r i a l s , STP 603, 1975, pp, 36-50.

2. Hedlin, C.P. Moisture Gains by Foam P l a s t i c Roof Insulations Under

Controlled Temperature Gradients. J. Cellular Plastics, Sept. / o G ~ . 1977, 313-19, 326.

TABLE 1

Moisture contents of glass fiber specimens under p a v i n g s t o n e s (Percentage by volume).

SOUTH SIDE NORTH S I D E

(300 x 1200 x 50 mu) (600 x 1200 x 50 mrn) Sampling

Dates

A B C D

coating1 Coating N o t Not

UP Down Coated Coated

E F

Coated Nor

Coated

~ - - ~ -

Specimens placed under paving stones

lcoating estimated to be 2 nun t h i c k

2610 x 1220 wn specimen removed and r e p l a c e d w i t h t w o

300 x 1200 mm specimens-Ell) with coating up, E ( 2 ) w i t h c o a t i n g

E D G E

OF

E D G E OF B U I L D I N G

T

100 x l M mm AND PARENT 610 x 1220 rnm SHEETS.

I

PIECES

610 x 1220

nm

SINCE

1973

T TEMPERATURE MEASURWENT LOCATION ( SEE FIG. 4 1

P L A N OF O U T D O O R T E S T B U I L D I N G , I N S U L A T E D W A L K W A Y , AND L O C A T I O N O F I N S U L A T I O N T E S T P I E C E S

h

1 1 1 1 1 1 1 1 1 1 1 1

A

a LARGE (1 .SPEC.I

A SMALL IAVG, FOR 4 SPEC. I

-

SMALL tAVG. FOR 2 SPEC. I

0 LARGE I 1 5PEC.I

- SMALL IAVG. FOR 4 SPEC. I

- L

-

CHAWGES I N MOISTURE COIUTENT IN E X T R U D E D P O L Y S T Y R E N E UNDER PAY I NG 'STONES

OSCrUTH S l D E OF B U I L D I N G N O R T H S l D E OF B U I L D I N G 1

I

-

i

7

I

I

!i 12 16 TIME OF D A Y . b

O U I S IDE A I R TEMPERATURES A N D TEMPERATURES A T INTERFACE

---

" P

w 12

-

z TOP VEhlTllArlON STARTING c I

13 MARCH 1979 pD- -- --d'

1

F I G U R E 5