How tight is tight enough?

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How tight is tight enough?

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Ser

TI11

W21d

National Research

Conseil national

1 *

1 Council Canada

de recherches Canada

c. 2

B I a G

Institute for

lnstitut de

-

- - - . ,

Research in

recherche en

Construction

construction

How Tight is

Tight

Enough?

by R.S. Dumont

Appeared in

Proceedings Healthy Buildings '88 Conference

Stockholm, Sweden 1988

,

Vol.

I. "State of the Art Reviews"

p.

61

-69

(IRC Paper No. 1571)

Reprinted with permission

NRCC 29769

u'

II

N R C

-

C I S n _I I

I

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f

1

L I B R A R Y

:( 4 t : a

F

EB 20

1989

P

I R C

i'

/

B I B L I O T H ~ Q U E

i

5 1 CNRC - IClST

3

(3)

Le document traite des fuites d'air dans les bltiment et des raisons de les rkduire au maximum. Les valeurs mesurdes au cours des essais d'ttanchCit6

P

I'air de maisons individuelles et de grands immeubles sont rapportCes. Pour les maisons individuelles, les fuites d'air varient de moins de 0.5 renouvellement d'air par heure

P

₅₀_{P a}₂₁_{plus de 50}

renouvellements d'air par heure

P

₅₀_{Pa. Pour les grands immeubles, un plus petit}

khantillonnage indique que le taux de fuite d'air par unit6 de surface &s immeubles variait de 0-6

P

5 ~ s * m 2

P

₇₅_Pa._U_{faut prendre soin, lors de 196tanchement}_{d'un immeuble, de}

veiller B _{ce que les niveaux de ventilation soient bien maintenus. En gtntral, on doit}

(4)

CIB Healthy Buildings

'88

Conf.

Stockholm September

1988

HOW TIGHT I S TIGHT

ENOUGH?

Robert S. Dumont

Institute for Research in Construction

National Research Council of Canada

Saskatoon, Saskatchewan

Canada

S7N OW9

Abstract

The

topic of air leakage in buildings is discussed. Reasons for

minimizing air leakage are presented. Measured values from tests of the

air leakage of groups of both detached residences and larger buildings

are given. ~or'detached

residences, air leakage measurements vary from

less than 0.5 air changes per hour at 50 Pa, to more than 50 air changes

per hour at 50

Pa.

For larger buildings, a small sample of measurements

indicated that the air leakage rate per unit surface area of the

buildings ranged from 0.6 to

5 ~ / s * m ~

at

75 Pa. Care

must be taken when

sealing a building to ensure that adequate levels of ventilation are

maintained.

Most often this is accomplished

by

providing mechanical

ventilation.

There is general agreement among building scientists that it is

desirable to build tight building envelopes, that is, envelopes with a

low air leakage rate. Considerable disagreement, however, can still

be

found on the question "Wow tight is tight enough?"

In the latter part of this paper the question of the appropriate

level of airtightness will

be

discussed in some detail. The following

1. Reasons for airtightness.

2. Different methods of reporting air leakage

of buildings.

3. Comparative air leakage values for

detached residences.

4. Comparative air leakage values for larger

buildings.

(5)

K e n s o ~ ~ s For A i r t i ~ l l t r ~ e s s

--

A ~rtunbcr o f reasoils a r e u s u a l l y c i t e t l f o r buil.ding a low leakage envelope. Usually tlre o n l y r e a s o n otre might choose n o t t o 11ave a t i g l r t envelope i s t o p r o v i d e n a t u r a l c o o l i n g i n a s t r u c t u r e . The u s u a l r e a s o n s f o r p r o v i d i n g a t i g h t envelope i n c l u d e t h e f o l l o w i n g :

1.

Damage t o t h e envelope from c o n d e n s a t i o n e f f e c t s o f a i r - b o r n e c o n v e c t i v e flow o f m o i s t u r e c a n be minimized.

2 . Energy consumption c a n be reduced by l i m i t i n g t h e amount of both s e n s i b l e and l a t e n t heat: t h a t must be provided t o temper t h e incoming a i r .

3 . H e a t recovery d e v i c e s - c a n b e used e f f e c t i v e l y on t h e

v e n t i l a t i o n a i r i f t h e envelope i s t i g h t .

4 . Noise t r a n s m i s s i o n through t h e envelope c a n be reduced.

Yet a n o t h e r advantage o f p r o v i d i n g a t i g h t envelope i s t h a t t h e t i g h t envelope c a n limit t h e e n t r y of d u s t , p o l l e n , and o t h e r a i r - b o r n e a l l e r g e n s and p o l l u t a n t s .

I n

a t i g h t b u i l d i n g , t h e a i r supply f o r t h e s t r u c t u r e c a n be c o n t r o l l e d more r e a d i l y , and i f d e s i r e d , t h e o u t s i d e a i r c a n be t r e a t e d b e f o r e

i t

e n t e r s t h e occupied s p a c e .

A i r Leakape Measurements Over t h e Years

Measurements have beerr made on t h e a i r leakap,e of envelopes and b u i l d i n g components f o r many y e a r s . The A i r I n f i l t r a t i o n and V e n t i l a t i o n C e n t r e ( A I V C ) h a s produced a s u b j e c t index ( 1 ) of p a p e r s on t h e a i r l e a k a g e of b u i l d i n g s . I n t h e i n d e x , t h e r e a r e 238 p a p e r s on t h e a i r l e a k a g e o f b u i l d i n g s , spanning t h e y e a r s from 1924 t o 1986. A graph showing t h e number o f papers w r i t t e n over t h e y e a r s on t h i s s u b j e c t i s shown i n f i g u r e

1.

A s c a n be s e e n , t h e r e c e n t y e a r s have s e e n a v e r y l a r g e amount of i n t e r e s t i n t h i s t o p i c , w i t h a peak of 38 papers p u b l i s h e d i n 1980. I n t h e A I V C s u b j e c t index d a t a b a s e t h e r e i s a l s o a breakdown of t e c h n i c a l p a p e r s on t h e a i r l e a k a g e of v a r i o u s b u i l d i n g components. A p i e c h a r t summarizing t h e d a t a i s g i v e n i n f i g u r e

2 .

A s c a n be s e e n , t h e s u b j e c t o f windows h a s been t h e most p o p u l a r t o p i c , w i t h 55% o f e l l t h e p a p e r s .

Measur

inn

A i r t i g l ~ t n e s s -

There a r e many d i f f e r e n t ways t h a t t h e a i r l e a k a g e of b u i l d i n g s have been r e p o r t e d . A summary o f d i f f e r e n t s t a n d a r d s f o r measuring t h e a i r '

leakage o f b u i l d i n g s and b u i l d i n g components i s c o n t a i n e d i n a 1984 document by Thompson ( 2 ) . Values of a i r l e a k a g e a t

1

p a s c a l , 4 p a s c a l s , 1 0 p a s c a l s , 50 p a s c a l s , and 75 p a s c a l s can a l l be found i n t h e l i t e r a t u r e . Leakages have been r e p o r t e d i n e q u i v a l e n t leakage a r e a s a t 10 p a s c a l s , e f f e c t i v e l e a k a g e a r e a s a t 4 p a s c a l s , a i r f l o w s , a i r flows p e r u n i t s u r f a c e a r e a , and a i r flows p e r u n i t volume.

(6)

done on smaller buildings such as detached residences. An equation of

the following form can be used to describe the air leakage:

where

Q

-

volumetric air flow (m3/s)

C

-

constant depending on size of

the openings (m3/s .pan)

~p

-

pressure difference (Pa)

n

-

exponent, ranging-between

0.5

and

1.0

On most pressure tests done on buildings, the index of determination

(

R

'

)

on the best fit linear regression of equation

(1)

can be measured

to 0.98 or better. Readings are usually taken over the range from about

5 pascals to about 100 pascals. Care must be taken during a pressure test

of

a component not to induce too great a positive or negative pressure on

I

the building, as some components can distort or fail under higher

'

pressure levels.

Perhaps the most comnon air leakage parameter that is reported for

houses and small buildings is the air changes per hour at 50 pascals.

Researchers in Sweden appear to have been the first to popularize this

number. This ntunber is convenient in that it is an air leakage number

normalized by the building volume. Comparisons between one building and

another can be readily made. A second advantage is the air leakage at

50

Pa is readily achievable in houses; a fan with a capacity of about 3 m3/s

can pressure test most houses to the

50

Pa level. Another advantage of

the 50 pascal number is that it can be used to estimate the approximate

air change of the building under natural conditions. Liddament(3) makes

the following observation: "Numerous experimental tests have shown that

the approximate air infiltration rate (in the absence of mechanical

ventilation) will be of the order of one twentieth of the measured air

change rate at

50 Pa

...

This provides a useful 'rule

of

thumb' should

pressurization test data be available."

A

disadvantage of the air changes per hour at 50 pascal number is

that the parameter is not a very useful one for larger buildings. In a

large building, the volume to surface area ratio is much larger than in a

detached residence, and the envelope leakage parameter that is of greater

value is the air leakage per unit surface area of the building. A more

popular parameter that has been used to report the air leakage of larger

buildings is the air flow per unit surface area at

a

pressure difference

of 75 Pa.

Is There a Universal Goal for Air Leakage for BuildingsZ

In this paper the author will not argue for a universal goal for air

leakage for buildings. Differing energy prices and climates often make it

(7)

i m p o s s i b l e t o s u g g e s t a s i n g l e s t a n d a r d f o r one c o u n t r y , l e t a l o n e f o r a l l c o u n t r i e s . Yet a n o t h e r confounding v a r i a b l e i s t h e use t o which t h e b u i l d i r ~ g is p u t . B u i l d i n g s w i t h moderate t o h i g h i n t e r i o r r e l a t i v e h u m i d i t i e s i n c o l d c l i m a t e s need t o be much b e t t e r s e a l e d t o l i m i t

c o n d e n s a t i o n problems t h a n do b u i l d i n g s w i t h low i n t e r i o r h u m i d i t i e s . I n s t e a d o f s u g g e s t i n g a u n i v e r s a l g o a l of a i r t i g h t n e s s , t h e a u t h o r w i l l p r e s e n t some measured v a l u e s o f a i r l e a k a g e f o r b o t h houses and l a r g e r b u i l d i n g s , and from t h e s e measurements one c a n g e t a f e e l i n g f o r tile a i r l e a k a g e v a l u e s t l l a t a r e a c h i e v a b l e under f i e l d c o n d i t i o r r s .

A i r Leakage Values f o r Residences

For d e t a c h e d r e s i d e n c e s , a l a r g e number o f a i r l e a k a g e measurements have been made. P e r s i l y ( 4 ) p r e s e n t s p r e s s u r e t e s t r e s u l t s from

11

d i f f e r e n t groups o f houses t e s t e d i n t h r e e c o u n t r i e s i n t h e Northern Hemisphere. The ..values a r e shown i n f i g u r e 3. A s mentioned e a r l i e r , t h e v a l u e s a r e commonly r e p o r t e d a s a i r changes p e r hour a t 50 Pa ( n 5 0 ) . A s may be s e e n from t h e f i g u r e , ' t h e n50 v a l u e s range from l e s s t h a n 0 . 5 t o

more t h a n 50 a i r changes p e r hour a t 50 Pa. ( I t s h o u l d be n o t e d t h a t 50 I p a s c a l s i s a l a r g e p r e s s u r e compared t o t h e p r e s s u r e t h a t

i s

e x e r t e d on a I l o w - r i s e b u i l d i n g by wind and - s t a c k e f f e c t s

.

For average c o n d i t i o n s t h e

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

l e s s t h a n about 5 p a s c a l s . ) A s c a n be s e e n from t h e f i g u r e , most of t h e _I groups of houses have average v a l u e s l e s s t h a n about 15 a i r changes p e r

hour a t 50 Pa, w i t h t h e e x c e p t i o n o f t h e group of 204 "low-income" houses i n t h e United S t a t e s . Houses i n t h e samples of Swedish and Canadian

houses b o t h e x h i b i t much lower v a l u e s o f a i r l e a k a g e . S i n c e 1977, new

i

detaclred houses i n Sweden have had a maximurn a l l o w a b l e a i r leakage r a t e

o f 3 . 0 a i r changes p e r hour a t 50 p a s c a l s . I n Canada, a f e d e r a l government sponsored v o l u n t a r y program ( t h e R-2000 program) f o r energy- e f f i c i e n t new houses h a s a maximum a l l o w a b l e a i r l e a k a g e r a t e o f 1 . 5 a i r changes p e r hour a t 50 P a . For program c o n t r o l p u r p o s e s , each i n d i v i d u a l house i n t h e Canadian R-2000 program is checked f o r compliance t o t h e a i r l e a k a g e s t a n d a r d by h a v i n g a p r e s s u r e t e s t done.

A s i l l u s t r a t e d by t h e s e t e s t r e s u l t s , i t i s p o s s i b l e t o reduce r e s i d e n t i a l a i r l e a k a g e v a l u e s t o l e s s t h a n

3

a i r changes p e r hour a t 50 Pa on a widespread b a s i s , a s i s t h e c a s e i n Sweden. Under a program of t r a i n i n g and q u a l i t y c o n t r o l , i t i s p o s s i b l e t o f u r t h e r reduce t h e a i r l e a k a g e v a l u e s t o l e s s t h a n 1 . 5 a i r changes p e r hour a t 50 Pa.

I t s h o u l d be n o t e d t h a t i n b o t h t h e newer Swedish houses and i n t h e . Canadian R-2000 programs t h a t t h e use o f c o n t r o l l e d mechanical v e r l t i l a t i o r l f o r r e s i d e n c e s i s a l s o mandated. A house w i t h an n50 v a l u e of 1 . 5 would t y p i c a l l y have a n a t u r a l a i r change r a t e l e s s t h a n about 0 . 1 a i r changes p e r h o u r , and t h i s i s about 1/3 t o 1/5 o f t h e recommended v e n t i l a t i o n r a t e f o r d w e l l i n g s . I n t h e absence of mechanical v e n t i l a t i o n , such t i g h t houses would be s e r i o u s l y u n d e r - v e n t i l a t e d .

(8)

detached houses is that such houses will be under-ventilated if

mechanical ventilation is not used. Although continuous mechanical

ventilation of larger buildings is very common in most countries these

days, continuous mechanical ventilation is not widespread in detached

residences in most countries.

For well-sealed houses that use a balanced mechanical ventilation

system with a heat recovery device such as an air to air heat exchanger,

it would seem prudent for energy conservation reasons to limit the amount

of uncontrolled air flow through the envelope.

If

the envelope is

tiglltened to an n50 value of 1.0, the approximate value of the

uncontrolled infiltration will be about 0.05 air changes per hour, or

approximately 1/10 of the total ventilation rate supplied (usually about

0.5 air changes per hour) by the heat recovery ventilator system. An

unbalanced heat recovery ventilator system as used in Swedish houses also

requires that the building envelope be tightly sealed. The slot vents

that are used on the windows rely on a relatively uniform negative

pressure throughout the house. If the envelope is leaky, under-

ventilation of some rooms can occur.

Air Leakage Values for Commercial Buildin~s

Far fewer measurements have been made of the air leakage rates of

buildings larger than detached residences. The U.S. National Association

of Arcllitectural Metal Manufacturers specifies a maximum leakage rate of

0.3 ~/s.ln~

at a pressure difference of 75 Pa for wall systems, exclusive

of leakage througl~

operable windows.

Such

a

low rate has rarely been

measured in actual buildings.

Measured air leakage in eight Canadian

office buildings (5) with sealed windows (assuming a flow exponent of

0.65 in equation 1) ranged from 0.61 to 2.4 ~ / s . m ~

at 75 Pa. More recent

measurements (6) in eight U.S. office buildings ranged from 1.1 to

5 ~ / s - m ~

at

75

Pa.

I

Tamura and Shaw (5) list typical air leakage values as follows:

L/s.m2 at 75 Pa

Tight

0.51 Average

1.5 Loose

3.1 For comparison purposes, a detached residence of size

8

x 12.5 x 5 m

(volume

-

500 m3; surface area

-

405 m2) with an air change rate of 1.0

air changes per hour at 50 Pa would have a leakage rate of 0.44 L/s m2 at

I

75 Pa. (assuming an exponent of 0.65 in equation 1.) Such a residence.

I

would be considered very well'sealed, and it is interesting to note that

I tl~e

envelope would also

be

considered tight using the above criteria

suggested by Tamura and Shaw (5).

Measurements indicate that large variations exist in the measured

air leakage rates of buildings.

(9)

For detached r e s i d e n c e s , t h e most commonly quoted v a l u e is t h e a i r changes p e r hour a t 50 p a s c a l v a l u e . Measured v a l u e s o f n50 range from l e s s that1 0 . 5 t o Inore than 5 0 . Programs i n Sweden have shown t h a t i t i s

p o s s ~ b 1 . e t o llroduce detncllcd 11ouses on a widespread b a s i s tllnt: have 1150 v a l u e s l e s s t h a n 3 . 0 .

For l a r g e r b u i l d i n g s , a r e l a t i v e l y common v a l u e t h a t i s quoted i s

t h e a i r l e a k a g e p e r u n i t s u r f a c e a r e a a t 75 p a s c a l s . Measurements on a s m a l l sample

01

b u i l d i n g s i n Canada and t h e United S t a t e s have been i n t h e range £;om 0 . 6 t o 5 L/s a m 2 . a t 7 5 Pa.

Care must be t a k e n w i t h t i g h t b u i l d i n g s t o e n s u r e t h a t adequate v e n t i l a t i o n i s m a i n t a i n e d . I n w e l l s e a l e d b u i l d i n g s , some form o f

mechanical v e n t i l a t i o n i s normally r e q u i r e d . I n such b u i l d i n g s , h e a t r e c o v e r y and t r e a t m e n t of t h e v e n t i l a t i o n a i r i s p o s s i b l e .

L i s t o f References

I.

B l a c k n e l l , J . "A s u b j e c t a n a l y s i s of t h e A I V C ' s b i b l i o g r a p h i c database--AIRBASE," T e c h n i c a l Note

A I V C

2 2 ,

A i r

I n f i l t r a t i o n and V e r i t i l a t i o n C e n t r e , Old B r a c k n e l l Cane West, B r a c k n e l l , B e r k s h i r e

R G 1 2

ItAll, G r e a t B r i t a i n , 1987.

2. Tllompson, C . "A review of b u i l d i n g a i r t i g h t n e s s and v e n t i l a t i o n s t a n d a f d s , " T e c h n i c a l Note A I C 1 4 , A i r I n f i l t r a t i o n and V e n t i l a t i o n C e n t r e , Old Brackrlell Lane West, B r a c k n e l l , B e r k s h i r e , RG12 4All, Grcnt B r i t a i n , 1984. 3. L i d d a m e n t

,

M . " A i r irlf i l t r a t i o n c a l c u l a t i o n techrriques-An a p p l i c a t i o n s g u i d e . " A i r I n f i l t r a t i o n and V e n t i l a t i o n C e n t r e , Old B r a c k n e l l Lane West, B r a c k n e l l , B e r k s h i r e , RG12 4N1, G r e a t B r i t a i n , 1 9 8 6 .

4 .

P e r s i l y , A . K . "Measurements of a i r i n f i l t r a t i o n and a i r t i g h t n e s s i n passivtt s o l a r homes." Measured

A i r

Leakage of B u i l d i n g s , ASTM STP 904, H . R . T r e c h s e l arld P . L. Lagus, e d . P h i l a d e l p h i a : American S o c i e t y f o r T e s t i n g and M a t e r i a l s , p . 4 6 , 1986.

5 .

Tamura, G.T. and Shaw, C . Y . " S t u d i e s on e x t e r i o r w a l l a i r t i g h t n e s s and a i r i n f i l t r a t i o n of t a l l b u i l d i n g s . " ASHWE T r a n s a c t i o n s , Vol 82, P t . 1 , p122, 1976.

6 . G r o t , R . A . and P e r s i l y , A . K . ,

"

Measured a i r i n f i l t r a t i o n and v e n t i l a t i o n r a t e s i n e i g h t l a r g e o f f i c e b u i l d i n g s . " Measured A i r Leakage of B u i l d i n g s , ASTM STP 904, H.R.Trechse1 and P.L. Lagus, e d . P l l i l a d e l p h i a : A~nerican S o c i e t y f o r T e s t i n g arld M a t e r i a l s , p . 151, 1986.

(10)

(11)

PERCENTAGES OF

AIR

LEAKAGE PAPERS

ON VARIOUS BUILDING COMPONENTS

Total

number

of

papers

=

121

F i g u ~ e

2 .

P e r c e n t a g e s o f a i r l e a k a g e ? a ? e r s o n v a r i o u s b u i l d i n g c o n p o n e n t s .

(12)

P a s s i v e s o l a r houses

6 9 I

-

_-

_Townhouses,

_{1 9 7 2} I 1

-

Detached homes, v a r i o u s a g e s

-

I I I 1 I I

I

w---

Freehold, Mid-1960's

w ~ o n v e n t i o n a l w ,

v a r i o u s a g e s

I

M ~ n e r g y - e f f i c i e ~ l t "

v a r i o u s

a g e s 2 0 4

l~Low-incomew homes

I

50

V)

8

4 0

low-energy detaciled

$ 2

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C o n s t r u c t i o n . A l i s t of b u i l d i n g p r a c t i c e and r e s e a r c h p u b l i c a t i o n s a v a i l a b l e from t h e I n s t i t u t e may be o b t a i n e d by w r i t i n g t o t h e P u b l i c a t i o n s S e c t i o n , I n s t i t u t e For R e s e a r c h i n C o n s t r u c t i o n , N a t i o n a l Research C o u n c i l of C a n a d a , Ottawa, O n t a r i o ,

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I n s t i t u t de r e c h e r c h e en construction. On p e u t o b t e n i r tlne l i s t e d r s p u b l i c a t i o n s d e 1 ' I n s t i t n t p o c t a n t s u r l e s t r c h n i q ~ r e s ou l e s r e c h e r c h e s e n matitre d e b z t i m e n t e n G c r i v a n t

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La S e c t i o n d e s p u b l i c a t i o n s , I n s t i t u t d e r e c h e r c h e e n c o n s t r u c t i o n , C o n s e i l n a t i o n a l d e r e c h e r c h e s du Canada, Ottawa ( O n t a r i o ) ,

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