Noise Control in Residential Buildings

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Noise Control in Residential Buildings

Ser mlr1 r l . ! J

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no. 23e

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NATIONAL RESEARCH COUNCIL CANADA

DIVISION OF BUILDING RESEARCH

NOISE CONTROL IN RESIDENTIAL BUILDINGS

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T. D. Northwood, H. B. Dickens, and A. T. Hansen

Summary of a seminar presented at the 1966 Annual Convention of the National House Builders Association in Montreal

J a n u a r y 1 1 , 1 9 6 6

AI.i A.LYZE

D

Technical Paper No. ?,30 of the

DIVISION OF BUILDING RESEARCH

OTTAWA F e b r u a r y 1 9 6 7

P R E F A C E

L a c k o f e f f e c t i v e n o i s e c o n t r o l i s c i t e d a s a

rnajor source of tenant complaint in multi-family dwellings and an important factor in the high rate of turnover in some r e n t a l p r o p e r t i e s . T h i s , c o r n b i n e d w i t h t h e c u r r e n t t r e n d t o m u l t i - f a m i l y h o u s i n g , h a s l e d t o i n c r e a s e d e r n p h a s i s b y b u i l d e r s o n t h e c o n t r o l o f n o i s e i n n e w c o n s t r u c t i o n a n d c o r r e s p o n d i n g l y a n e e d f o r r e l i a b l e t e c h n i c a l i n f o r m a t i o n on the subject. T o r n e e t t h i s n e e d t h e D i v i s i o n o f B u i l d i n g R e s e a r c h , w o r k i n g t h r o u g h t h e R e s e a r c h C o m m i t t e e a n d t h e M a n u f a c t u r e r s r C o u n c i l o f t h e N a t i o n a l H o u s e B u i l d e r s A s s o c i a t i o n , p r e s e n t e d a s e m i n a r o n r r N o i s e C o n t r o l i n R e s i d e n t i a l C o n s t r u c t i o n f l at the NHBA annual rneeting in Montreal in January 1966" T h e D i v i s i o n t s c o n t r i b u t i o n s , w h i c h w e r e p r e s e n t e d b y

T . D . N o r t h w o o d , B u i l d i n g P h y s i c s S e c t i o n , a n d H . B . D i c k e n s and A. T. Hansen, Housing Section, forrn the subject rnatter o f t h i s p a p e r .

Ottawa

F e b r u a r y 1 9 6 7

R. F. Legget, D i r e c t o r .

T A B L E O F C O N T E N T S

SOUND AND NOISE

H e a r i n g - the Decibel Scale Sound in Buildings

S o u n d B a r r i e r s

S o u n d T r a n s m i s s i o n C l a s s Irnpact Sound

How Much Sound Insulation is Needed?

SITING AND LAYOUT OF BUILDING

Windows P a g e I

z

6

9

1 0

Control of Indoor Noise Open Planning

Door s

SOUND TRANSMISSION THROUGH Sorne Typical Constructions SOUND TRANSMISSION THROUGH

Sorne Typical Constructions NOISE IN MECHANICAL SYSTEMS

Equiprnent Noise N o i s e i n P i p i n g N o i s e i n D u c t s WALI-S FLOORS 1 1 t 3 l 6 T 7

r 9

CONSTRUCTION PRACTICES THAT DECREASE

NOISE CONTROL iN RESIDENTIAL BUILDINGS b y

T . D . N o r t h w o o d , H . B . D i c k e n s , a n d A . T . H a n s e n

A tenant may be attracted to a new apartment building by the splendid lobby, the sauna bath or the swimming pool, but whether he stays or not will probably depend on less obvious arnenities. One of the rnost important is adequate p r o t e c t i o n f r o m n o i s e . E v e n t h e o c c u p a n t o f a s i n g l e - f a m i l y dwelling rnay yearn for a quiet refuge from the prattle of h i s c h i l d r e n o r o f t h e i r t r a n s i s t o r r a d i o .

Recognizing the irnportance of sound insulation, the National House Builders Association invited the Division of B u i l d i n g R e s e a r c h t o p r e s e n t a s e m i n a r o n t h i s s u b j e c t a t the NHBA Annual Meeting in Montreal in January 1966" T h e s u b s t a n c e o f t h a t p r e s e n t a t i o n i s r e c o r d e d h e r e . T h e p a p e r s c o n s i d e r , s t e p b y s t e p , t h e p r o p e r t i e s o f

typical sounds and how they are transmitted within buildings, the acoustical requirernents for adequate protection of

t h e o c c u p a n t s , a n d t h e p r a c t i c a l m e t h o d s o f d e s i g n a n d c o n s t r u c t i o n t h a t w i l l m e e t t h e s e r e q u i r e m e n t s . A b i b l i o -graphy of other relevant publications has been included at the end of this report.

SOUND AND NOISE

B e f o r e c o n s i d e r i n g a c t u a l c o n s t r u c t i o n d e t a i l s , i t w i l l b e a u s e f u l p r e l i r n i n a r y t o e s t a b l i s h t h e v o c a b u l a r y u s e d in describing sound waves and in evaluating noise control p r o b l e r n s .

A sound wave reaches the ear as a rninute fluctuation i n a i r p r e s s u r e w h i c h c a n b e r e p r e s e n t e d g r a p h i c a l l y a s s h o w n in Figure l" One complete fluctuation of the wave is a cycle, a n d t h e n u m b e r o f c y c l e s p e r s e c o n d i s t h e f r e q u e n c y o r p i t c h of the sound. The rnovernent of a sound wave through air c a n b e c o m p a r e d w i t h a r i p p l e o n t h e s u r f a c e o f w a t e r ; t h e d i s t a n c e f r o m p e a k t o p e a k i s k n o w n a s t h e w a v e l e n g t h .

- z

T h e s i m p l e f l u c t u a t i o n s h o w n i n F i g u r e I r e p r e s e n t s a s i n g l e f r e q u e n c y . M o s t s o u n d s c o n t a i n m a n y f r e q u e n c i e s a n d t h e i r g r a p h s l o o k r n o r e l i k e t h o s e s h o w n i n F i g u r e 2 , but the individual frequency components can be dealt with one at a tirne in acoustical calculations. The relative

i m p o r t a n c e o f t h e v a r i o u s f r e q u e n c i e s i n s o m e t y p i c a l s o u n d s a r e d e p i c t e d i n s o u n d s p e c t r a , a s i l l u s t r a t e d i n F i g u r e 3 . Note that most of the power in spe.ech is around 400 cycles per second. The intelligibility _{of $Eech depends mainly,} however, on a slightly higher frequency band. Footsteps have a somewhat sirnilar spectrum, although for a wood j o i s t f l o o r t h e r e w o u l d b e more low frequency energy than f o r t h e c o n c r e t e f l o o r i l l u s t r a t e d h e r e .

T h e w a v e l e n g t h c o r r e s p o n d i n g t o e a c h f r e q u e n c y is shown at the top of Figure 3, and it will be seen that the wavelengths of interest range frorn ? in. to about l0 ft. Generally the efficiency of a source in radiating sound d e p e n d s o n i t s s i z e r e l a t i v e t o a w a v e l e n g t h . T h u s , a vibrating body only a few inches in diarneter will not radiate much low frequency sound. But if it is attached t o a l a r g e r a d i a t i n g s u r f a c e i t w i l l t h e n p r o d u c e m u c h rrrore low frequency sound.

A s o u n d b e c o m e s a n o i s e w h e n i t i n t e r f e r e s w i t h onecs own activities. If it is too loud, it,rnakes it difficult t o c o n v e r s e w i t h p e o p l e , o r l i s t e n t o m r r s i c , o r s 1 e e p . Even when it is not very loud, it will intrude if it conveys any kind of message. Speech that is intelligible, or nearly so, i s c e r t a i n l y t h e w o r s t o f f e n d e r . F o o t s t e p s a r e a n n o y i n g

because of their sharp impulsive quality, and the directional e f f e c t s a s s o c i a t e d w i t h t h e m . O n e o f t h e c l a s s i c e x a m p l e s i s t h e s o u n d o f o n e s h o e d r o p p i n g ; t h e m e s s a g e i t c o n v e y s i s t h a t t h e r e w i I I p r o b a b l y b e a s e c o n d o n e . H e a r i n g - T h e D e c i b e l Scale F i g u r e 4 i n d i c a t e s t h e r a n g e o f f r e q u e n c i e s a n d s o u n d l e v e l s t h a t c a n b e h e a r d . T h e d e c i b e l s c a l e i s u s e f u l i n t h i s c o n t e x t b e c a u s e i t c o r r e s p o n d s c l o s e l y t o t h e w a y v a r i a t i o n s i n i n t e n s i t y o r l o u d n e s s a r e p e r c e i v e d . T h e e a r r e c o g n i z e s p e r c e n t a g e c h a n g e s r a t h e r t h a n a b s o l u t e d i f f e r e n c e s i n p r e s s u r e . T h e m i n i r n u r r r c h a n g e p e r c e i v e d u n d e r l a b o r a t o r y c o n d i t i o n s i s a b o u t I d B w h i c h c o r r e s p o n d s t o a l 0 p e r c e n t c h a n g e i n s o u n d p r e s s u r e . I n a c t u a l s i t u a t i o n s 2 o r 3 d B i s a v e r y s m a l l c h a n g e ; 1 0 d B i s a s u b s t a n t i a l c h a n g e .

- 3

T}:.e zer o on the sound level scale is arbitrarily set to about the minimum one can hear in a very quiet laboratory

environment. More typically, even in quiet situations, there is usually a background level of noise amounting to

a t l e a s t 1 0 o r l 5 d B , r r r o r e o f t e n 3 0 t o 4 0 d B . C o n v e r s a t i o n a l s p e e c h a v e r a g e s a b o u t 7 0 d B . A s u c c e s s f u l c o c k t a i l p a r t y can approach 85 dB but this is still below the threshold of p a i n w h i c h i s a r o u n d 1 3 0 d B .

Sound in Buildings

The sound level in a roorn depends not only on the

power of the source, but also on the amount of sound absorption i n t h e r o o m . A b s o r p t i o n m a y b e p r o v i d e d b y f u r n i s h i n g s ,

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

rnaterial. This is a good point at which to consider how rnuch one can accomplish by absorption treatment in the source r o o r n i t s e l f . T o a c h i e v e a I 0 d B r e d u c t i o n i n s o u n d I e v e l , the absorption must be multiplied by a factor of 10. Perhaps this can be done in a kitchen or bathroorn or a particularly bare playroom, but in a reasonably furnished bedroom or living room, it will be difficult even to double the absorption w h i c h w o u l d r e d u c e t h e n o i s e b y o n l y 3 d B . A n o t h e r p r o b l e m with this approach to noise control is the fact that some types o f n o i s e s o u r c e s a d a p t t h e m s e l v e s t o t h e i r s u r r o u n d i n g s . F o r e x a m p l e , t h e n o i s e l e v e l p r o d u c e d b y a r a d i o o r T V s e t is deteri'nined by the listener and the volume control rather than by the amount of absorption in a roornc

S o u n d B a r r i e r s

The most effective means of controlling the propagation of sound in a building is to erect walls and floors that act a s g o o d b a r r i e r s t o s o u n d " T h e f i r s t r e q u i r e m e n t o f a b a r r i e r is that it be impermeable. A wall built of porous block,

for example, is not very effective because the sound actually t r a v e l s t h r o u g h t h e p o r e s o f t h e r n a t e r i a l , u n l e s s t h e y a r e sealed at some point in the path by plaster or heavy paint. T h e n e x t d e s i r a b l e v i r t u e i s w e i g h t : t h e s o u n d t r a n s m i s s i o n loss of a single wall increases by roughly 5 dB when the weight is doubled. The top curve in Figure 5 illustrates what one can achieve with a f -in. brick wall. This is about the practical lirnit that can be achieved by weight alone.

- 4

Another approach is to use a multiplicity of walls with a minimurn o f c o u p l i n g b e t w e e n t h e m . A t y p i c a l s t u d w a l l c o n s i s t s e s s e n t i a l l y o f t w o w a l l s , b u t t h e y a r e c o n n e c t e d t o s o m e e x t e n t b y a s t u d

f r a r n e w o r k a n d a l s o b y t h e a i r c o n f i n e d b e t w e e n t h e m . C o n s i d e r a t i o n will be given later to the effects of these two types of coupling

o n t h e p e r f o r r n a n c e o f s t u d w a l l s .

In addition to weight and impermeability, the other factor of importance in a wall is its flexural stiffness.

Unfortunately, stiffness is not usually a virtue. In the case of thin panels or lightweightTeasonry, stiffness is responsible for what is known as a rrcoincidence dipil in the transmission loss curve. The perforrrrance of a lightweight masonry wall shown in Figure 5 exernplifies this with a bad rnid-frequency s l u m p i n p e r f o r m a n c e . S i m i l a r l y , t h e p l a s t e r l a y e r s o f t h e stud waII show a very characteristic coincidence dip in the high frequency range.

S o u n d T r a n s r n i s s i o n C I a s s

Another point to observe in Figure 5 is that the

t r a n s m i s s i o n l o s s v a r i e s m a r k e d l y o v e r t h e f r e q u e n c y r a n g e . ClearIy, there is a problem in cornparing the insulation

p e r f o r m a n c e s t o b e e > c p e c t e d fr o m t h e s e t h r e e w a l l s . I n t h e o l d d a y s i t w a s c u s t o m a r y t o t a k e a s i m p l e a v e r a g e o f m e a s u r e m e n t s m a d e a t c e r t a i n s t a n d a r d f r e q u e n c i e s . T h i s m a y b e r a t h e r m i s l e a d i n g , h o w e v e r , i f t h e t r a n s r n i s s i o n l o s s v a r i e s i r r e g u l a r l y a s i n d i c a t e d b y t h e b r o k e n c u r v e " T h e a v e r a g e o f t h e t r a n s m i s s i o n l o s s m e a s u r e m e n t s f o r the lightweight masonry wall appears good because of the

s a t i s f a c t o r y p e r f o r m a n c e a t v e r y h i g h f r e q u e n c i e s , b u t this says nothing about its poor performance in the important middle frequency range. The other difficulty about averages is that about 57 kinds of averages have been used, by various p e o p l e a t v a r i o u s t i r n e s . O n e m u s t , t h e r e f o r e , b e c a u t i o u s i n i n t e r p r e t i n g a v e r a g e f i g u r e s i n t r a d e l i t e r a t u r e .

Acoustical experts now rely on a new type of rating w h i c h p r o v i d e s a m o r e r e l i a b l e f i g u r e o f m e r i t f o r t h e c o m m o n sound insulation applications -- Sound Transmission Class (STC). The classification procedure involves comparing the actual

t r a n s m i s s i o n l o s s c u r v e w i t h a s e t o f S T C c o n t o u r s s i m i l a r to the one shown in Figure 5. In effect, the procedure is t o c o n s i d e r o n l y t h e l o w p a r t s o f t h e t r a n s r n i s s i o n l o s s c u r v e relative to this contour.

- 9 Impact Sound S o f a r t h e d i s c u s s i o n h a s b e e n r e l a t e d p r i m a r i l y t o a i r b o r n e s o u n d s , t h a t i s , s o u n d s , s u c h a s v o i c e s , t h a t t r a v e l t h r o u g h t h e a i r b e f o r e t h e y i m p i n g e o n t h e b o u n d a r i e s o f a r o o r r r . A n o t h e r e q u a l l y i m p o r t a n t c a t e g o r y i s i m p a c t s o u n d s s u c h a s f o o t s t e p s , w h i c h o r i g i n a t e a s v i b r a t i o n s i n t h e s t r u c t u r e i t s e l f . T h e a s s e s s r n e n t o f i r n p a c t s o u n d s i s n o t a s c u t a n d dried as one would like, but there is an international standard t e s t , a n d s e v e r a l r a t i n g s c h e m e s s i r n i l a r t o t h e S T C s y s t e m . T h e I m p a c t N o i s e R a t i n g ( I N R ) d e v e l o p e d b y t h e U . S . F e d e r a l H o u s i n g A d m i n i s t r a t i o n , w h i c h i s n o w w i d e l y u s e d i n t h e U n i t e d S t a t e s , w i l l b e r e f e r r e d t o l a t e r i n c o r n p a r i s o n s o f d i f f e r e n t f l o o r c o n s t r u c t i o n s . H o w M u c h S o u n d I n s u l a t i o n i s N e e d e d ? I n p r i n c i p l e a t l e a s t o n e c a n c o n t r o l t h e s o u n d s p r o d u c e d i n o n e l 6 o w n d w e l l i n g , s o t h i s d i s c u s s i o n w i l l c o n c e n t r a t e o n p a r t y w a l l s a n d f l o o r s i n m u l t i p l e d w e l l i n g s . Ideally, the arnount of sound insulation should at least equal t h e d i f f e r e n c e i n n o i s e s p e c t r a b e t w e e n t h e n o i s y a p a r t m e n t a n d t h e q u i e t o n e . T h e n t h e n o i s e t h a t p e n e t r a t e s t o t h e q u i e t s i d e w i l l n o t b e h e a r d . O n t h e n o i s y s i d e t y p i c a l n o i s e s w i I I b e T V , v o i c e s , a n d s o o n . l n t h e m o s t c r i t i c a l c a s e s t h e b a c k g r o u n d l e v e l o n t h e q u i e t s i d e w i l l c o n s i s t o f a r a n d o r n c o l l e c t i o n o f n o i s e s t r a n s m i t t e d f r o m o u t d o o r s a n d from distant parts of the building. Incidentally, a Swedish survey showed that if a building fronts on a busy thoroughfare, the people who overlook the street cornplain about traffic noise but not about their neighbours; but the people at the back of the building cornplain about the neighbours.

F o r t y p i c a l n o i s e s a n d b a c k g r o u n d c o n d i t i o n s , a b o u t t w o - t h i r d s o f t h e t e n a n t s w i l l b e s a t i s f i e d m o s t o f t h e t i m e i f a n i n s u l a t i o n o f S T C 5 0 i s p r o v i d e d b e t w e e n c r i t i c a l a r e a s s u c h a s b e d r o o m s o r l i v i n g r o o r n s . T h i s , b y t h e w a y , w i l l s t i l l b e i n a d e q u a t e f o r s e p a r a t i n g , s a y , k i t c h e n s f r o m b e d r o o m s . I n R e s i d e n t i a l S t a n d a r d s * t h e r n i n i m u r n r e q u i r e m e n t i s S T C 4 5 , but about half the occupants of such a building will sometimes

f i n d i t i n a d e q u a t e ; f o r l e s s t h a n S T C 4 5 , t h e p e r c e n t a g e a n d d e g r e e o f d i s s a t i s f a c t i o n i n c r e a s e s v e r y r a p i d l y . A t t h e u p p e r e x t r e m e , the practical maximum that can be achieved in a waII is about S T C 5 5 , a n d t h i s r e q u i r e s g r e a t c a r e i n c o n s t r u c t i o n d e t a i l s . 'l Residential Standards,

National Building Code

Suppl.ernent No. 5 to the o f C a n a d a 1 9 6 5 , N R C 8 2 5 I .

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T h e r e i s c o n s i d e r a b l y I e s s i n f o r m a t i o n a v a i l a b l e a b o u t i m p a c t n o i s e , b u t i t a p p e a r s t h a t a r e c o m m e n d e d v a l u e of the Impact Noise Rating would be zer o or better. An INR o f - 1 0 s h o u l d b e r e g a r d e d a s t h e r o c k - b o t t o m m i n i m u m , about equivalent to the airborne requirement of STC 45.

SITING AND LAYOUT OF BUILDING

The location and interior layout of a building can g r e a t l y i n f l u e n c e t h e n o i s e p r o b l e m a n d i t i s i r n p o r t a n t t o b e g i n n o i s e c o n t r o l a t t h e p l a n n i n g s t a g e .

Flexibility in site layout is often limited but where o u t d o o r n o i s e l e v e l s a r e h i g h t h e f o l l o w i n g c a n a s s i s t i n r e d u c i n g t h e i r e f f e c t :

L o c a t e t h e b u i l d i n g a s f a r f r o m n o i s e s o u r c e a s p o s s i b l e . T h e n o i s e l e v e l d r o p s a b o u t 6 d B e a c h t i m e t h e d i s t a n c e i s d o u b l e d . Take advantage of hills, highway cuts or

o t h e r b u i l d i n g s t o p r o v i d e s o u n d b a r r i e r s . Note that trees or shrubs are of little value a s b a r r i e r s t h o u g h t h e y m a y p r o v i d e s o m e a b s o r p t i o n o f s o u n d . L o c a t e n o n c r i t i c a l a r e a s s u c h a s c o r r i d o r s , k i t c h e n s , b a t h r o o m s , e l e v a t o r s a n d s e r v i c e s p a c e s o n t h e n o i s y s i d e a n d c r i t i c a l a r e a s s u c h a s b e d r o o r n s a n d I i v i n g s p a c e s o n t h e q u i e t s i d e . 4 . K e e p w i n d o w s a w a y f r o m t h e n o i s y s i d e o f a b u i l d i n g w h e r e v e r p o s s i b l e . Windows W i n d o w s a r e t h e w e a k e s t p a r t o f e x t e r i o r w a l l s i n t e r m s o f s o u n d c o n t r o l . T h e i r e f f e c t i v e n e s s i s d i r e c t l y related to the over -all air tightness of the installation. T h i s i s t h e r e a s o n w h y f i x e d w i n d o w s a r e b e t t e r f o r s o u n d c o n t r o l t h a n o p e n a b l e w i n d o w s . F i x e d s i n g l e glazing is about as good acoustically as openable double glazing (Figure 6). Most fixed double gLazing is in the r a n g e o f S T C 3 0 t o 3 5 a n d t h i s i n c r e a s e s a s t h e s p a c e

t .

z.

- 7 b e t w e e n t h e p a n e s i s i n c r e a s e d . F o r a r e l a t i v e l y h i g h d e g r e e o f s o u n d c o n t r o l ( a n S T C o f o v e r 4 0 ) i t i s n e c e s s a r y t o p r o v i d e t w o p a n e s o f g l a s s s e p a r a t e d b y a t l e a s t a n 8 - i n . s p a c e n o t a v e r y p r a c t i c a l s i t u a t i o n i n m o s t c a s e s . T h e r e i s a f u n d a r n e n t a l d i f f e r e n c e i n t h i s r e g a r d b e t w e e n h e a t a n d n o i s e control. For thermal insulation there is little advantage in an air space larger than 3/4 in.

s u m m a r y : K e e p w i n d o w s o n n o i s y s i d e o f b u i l d i n g s t o a m i n i m u m Z . U s e s e a l e d u n i t s w h e r e v e r p o s s i b l e In

t .

Make sure that movable windows are well w e a t h e r s t r i p p e d t o r e d u c e a i r l e a k a g e . I n d o o r N o i s e

Much can be done with the interior layout of buildings t o c o n t r o l n o i s e i n t h e m o r e c r i t i c a l a r e a s .

In apartment buildings the stacking of identical units o n s u c c e s s i v e f l o o r s o n e a b o v e t h e o t h e r s o t h a t k i t c h e n s a r e o v e r k i t c h e n s a n d b a t h r o o m s a r e o v e r b a t h r o o m s c a n a i d c o n s i d e r a b l y i n n o i s e c o n t r o l . T h e s e a r e n o t o n l y n o i s y a r e a s b u t f r e q u e n t l y h a v e h a r d s u r f a c e f l o o r s w h i c h t e n d t o i n c r e a s e t h e p r o b l e m o f i r n p a c t s o u n d t r a n s m i s s i o n w h i c h i s a s o u r c e of frequent complaints in existing apartrnents. Such problems a r e c o s t l y t o c o n t r o l b y c o n s t r u c t i o n m e t h o d s .

The floor problem can be minimized between units in apartment buildings by placing each apartment unit on two floors with the bedroorns of each on the lower level below their own living areas" This could still result in

some impact noise problerns within the unit itself but a t l e a s t c o n f i n e s t h e p r o b l e m t o o n e o c c u p a r l c y w h e r e t h e o c c u p a n t s c a n e x e r c i s e s o m e d e g r e e o f c o n t r o l .

For all apartrnents, except perhaps the small efficiency type, the layout of each floor can usually be planned so that quiet areas in one apartrnent ate separated

- B s t a i r w a y s , h a l l s a n d k i t c h e n s . I f t h i s i s d o n e t h e S T C 4 5 p a r t y w a l l m a y b e a d e q u a t e . W h e r e t h i s a r r a n g e r r r e n t i s n o t p o s s i b l e t h e b e s t a l t e r n a t i v e i s t o p l a c e q u i e t a r e a s s u c h a s b e d r o o m s a d j a c e n t t o s i m i l a r a r e a s i n t h e n e x t a p a r t m e n t a n d t o p r o v i d e a n S T C 5 0 p a r t y w a l l b e t w e e n . T h e w o r s t a r r a n g e r r r e n t i s t o p l a c e n o i s y a r e a s o f o n e u n i t next to quiet areas of the neighbouring unit (for example, k i t c h e n s n e x t t o t h e n e i g h b o u r s l b e d r o o m ) . I n t h i s c a s e even an STC 50 wall would probably be inadequate.

An example of a poorly planned unit is shown in Figure 7. In this layout the bedroom, which should be a q u i e t a r e a , i s n e x t t o t h e e l e v a t o r a n d a l s o a d j a c e n t t o t h e n e i g h b o u r t s k i t c h e n . T h e c h o i c e s t a r e a s w h i c h a r e b u f f e r e d f r o m t h e n e i g h b o u r i n g n o i s e a r e o c c u p i e d b y the bathroorn and kitchen which are noncritical roorrrs. In contrast Figure 8 shows a well-planned layout with the noncritical areas such as kitchen and bathroorn a c t i n g a s b u f f e r s a g a i n s t u n w a n t e d n o i s e .

The plumbing fixtures serving kitchen and

b a t h r o o m s a r e p a r t i c u l a r L y f t o u b l e s o r n e s o u r c e s o f n o i s e . T h e p r o b l e m c a n b e r n i n i m i z e d b y p l a c i n g k i t c h e n s a n d b a t h r o o m s o f a d j a c e n t u n i t s b a c k - t o - b a c k a n d o n e a b o v e t h e o t h e r w i t h t h e s e r v i c e s i n a w a l l a w a y f r o m t h e c r i t i c a l r o o r n s . M e t h o d s o f h a n d l i n g t h e s p e c i a l n o i s e p r o b l e m s a r i s i n g f r o m m e c h a n i c a l a n d e l e c t r i c a l s e r v i c e s w i I I b e d i s c u s s e d l a t e r . I t i s p a r t i c u l a r l y i r n p o r t a n t i n p l a n n i n g , h o w e v e r , t o l o c a t e f u r n a c e s , p u r r t p s , c o r r t p r e s s o r s , fans, and laundry equipment away from quiet areas such as b e d r o o r n s " I n h i g h - r i s e a p a r t m e n t s t h e l o c a t i o n o f e l e v a t o r s a n d i n c i n e r a t o r c h u t e s s h o u l d b e g i v e n c a r e f u l c o n s i d e r a t i o n . E l e v a t o r s a r e a s p e c i a l p r o b l e m s i n c e t h e y m a y c a u s e n o i s e or vibration throughout the entire building.

T h e p l a n n i n g p r i n c i p l e s u s e d i n t h e c o n t r o l o f n o i s e b e t w e e n a p a r t m e n t s c a n a l s o b e e f f e c t i v e i n c o n t r o l l i n g n o i s e w i t h i n a s i n g l e o c c u p a n c y . _{T h i s i s i l l u s t r a t e d i n F i g u r e 9 .} N o t e t h a t : I . T h e n o i s y a r e a s , b a t h r o o m s , s t a i r s , k i t c h e n s a n d b a c k e n t r a n c e s , a r e g r o u p e d a n d t h e b a t h r o o m s a r e b a c k t o b a c k "

9

-The comrnon bathroom partition or the bathr oom -kitchen partition allows t h e p l u m b i n g s t a c k t o b e i s o l a t e d frorn the quiet areas.

S l e e p i n g a n d l i v i n g a r e a s a r e s e p a r a t e d , with the bedroom on the lower left b e i n g t h e q u i e t e s t r o o m .

C l o t h e s c l o s e t s a r e a r r a r a g e d t o a c t a s s o u n d b a r r i e r s .

5 . S l e e p i n g a r e a s a r e s e p a r a t e d f r o m l i v i n g a r e a s by an extra door in the hallway.

With care in planning the partitions within a dwelling p l u s o n e o r t w o e x t r a d o o r s w i I I s e r v e a s s o u n d b a r r i e r s to divide the dwelling into zones of acoustical privacy. T h e t y p i c a l s t u d p a r t i t i o n i s a f a i r l y a d e q u a t e n o i s e b a r r i e r within a dwelling (but not between dwellings) provided it is not made ineffective by heating ducts, openings around e l e c t r i c a l f i x t u r e s , o r b y p o o r l y f i t t i n g d o o r s .

Open Planning

The trend to open planning in house layout is a trend a w a y f r o r n a c o u s t i c a l p r i v a c y . F o r t h e c o n t r o l o f n o i s e there is no substitute for a wall or a door. As a minimum the open plan should be rnodified by separating off one quiet

z o n e s u c h a s t h e b e d r o o r n a r e a f r o m t h e r e r n a i n d e r o f t h e h o u s e ( F i g u r e 9 ) . W i t h i n t h e o p e n p l a n o n e c a n t e m p e r n o i s e p r o b l e r n s b y s u i t a b l e s p a c e a r r a n g e m e n t a n d b y a j u d i c i o u s u s e o f acoustical materials. T r a n s r n i t t e d n o i s e l e v e l s w i l l n o t u s u a l l y b e r e d u c e d b y m o r e t h a n 5 o r l 0 d B by this rneans, but at least the sharp edge can be taken off s o u n d s s u c h a s t h e c l a t t e r o f d i s h e s . T h e k i t c h e n , i n f a c t , i s a g o o d p l a c e t o c o n s i d e r t h e a p p l i c a t i o n o f a c o u s t i c a l m a t e r i a l . A n o t h e r u s e f u l a r e a i s a h a l l w a y o r f o y e r s e p a r a t i n g n o i s y f r o m c r i t i c a l z o n e s " T h i s i s e s p e c i a l l y h e l p f u l i f a d i r e c t l i n e o f s i g h t t o t h e n o i s e s o u r c e i s a v o i d e d . D o o r s D o o r s a r e g e n e r a l l y t h e w e a k l i n k i n t h e c o n t r o l o f s o u n d b e t w e e n r o o m s a n d c o n s e q u e n t l y t h e y d e t e r m i n e t h e d e g r e e o f s o u n d p r i v a c y t h a t c a n b e a c h i e v e d . A t y p i c a l d o o r rpay have an S T C l 5 t o 2 0 c o m p a r e d w i t h S T C 3 0 t o 3 5 f o r a s t a n d a r d s t u d p a r t i t i o n w i t h d r y w a l l . w h e r e d o o r s a r e u s e d i n a w a l l t h e r e i s

z .

- l 0 n o a d v a n t a g e i n i n c r e a s i n g t h e S T C o f t h e p a r t i t i o n . T h e s i t u a t i o n c o u l d b e i m p r o v e d b y u s i n g a h e a v i e r ( s o l i d c o r e ) d o o r a n d p r o v i d i n g g a s k e t i n g t o c o n t r o l a i r l e a k a g e a l t h o u g h t h i s w o u l d b e o f r e d u c e d v a l u e w h e r e t h e d o o r m u s t b e u n d e r c u t t o a l l o w f o r r e t u r n a i r f l o w i n h e a t i n g o r v e n t i l a t i n g s y s t e m s . A g a s k e t i n s t a l l e d b e t w e e n t h e d o o r a n d j a m b c a n a l s o a s s i s t b y s o f t e n i n g t h e i r n p a c t w h e n t h e d o o r i s s l a m m e d . T h i s i s a p a r t i c u -I a r -I y u s e f u l t r e a t r n e n t f o r d o o r s t o a p a r t m e n t s f r o m c o r r m o n h a -I l s . W h e r e v e r p o s s i b l e d o o r s t o s u c h h a l l s s h o u l d b e o f f s e t s o t h a t n o i s e i s n o t r a d i a t e d d i r e c t l y a c r o s s f r o m o n e d o o r t o a n o t h e r . T h e u s e o f c a r p e t s o n t h e f l o o r a n d a c o u s t i c t i l e o n t h e c e i l i n g w i l l a i d i n sound control within the corridor and rnake it a useful buffer zone b e t w e e n a p a r t m e n t s .

SOUND TRANSMISSION THROUGH WALLS

T h e e f f e c t i v e n e s s o f a s i n g l e l a y e r w a l l , s u c h a s u n i t m a s o n r y , c o n c r e t e o r s o l i d g y p s u r n , i n r e s i s t i n g s o u n d d e p e n d s m a i n l y o n i t s weight. Other things being equal, doubling the weight increases the t r a n s m i s s i o n l o s s b y a b o u t 5 d B . O n e m u s t , h o w e v e r , c o n s i d e r a l s o t h e s t i f f n e s s o f a w a l l w h i c h i s r e s p o n s i b l e f o r a d r o p i n t r a n s m i s s i o n l o s s i n a c e r t a i n f r e q u e n c y r a n g e . T h i c k e n i n g a w a l 1 , t h e r e b y i n c r e a s i n g b o t h w e i g h t a n d s t i f f n e s s , t h e r e f o r e w i l l n o t n e c e s s a r i l y i r n p r o v e i t i f t h e s t i f f n e s s e f f e c t i s b r o u g h t i n t o a r n o r e c r i t i c a l f r e q u e n c y r a n g e . A m a s o n r y w a l l o f g i v e n w e i g h t p e r s q u a r e f o o t w i l l p r o v i d e b e t t e r p e r f o r m a n c e i f i t i s c o n s t r u c t e d a s a c a v i t y w a l l r a t h e r t h a n a s a s i n g l e h o s p o g e n e o u s l a y e r . T h e n t h e s y s t e m b e c o m e s t w o r n a s s i v e l a y e r s c o u p l e d t o g e t h e r o n l y b y t h e c o m p r e s s i b i l i t y o f t h e c o n f i n e d a i r s p a c e . T h e i r n p r o v e m e n t d u e t o t h e a i r s p a c e m a y b e s p o i l e d , h o w e v e r , i f t h e t w o l a y e r s a r e c o n n e c t e d b y a l a r g e n u m b e r o f r i g i d t i e s . T i e s s h o u l d b e u s e d a s s p a r i n g l y a s possible and should be relatively flexible. Coupling through the air

s p a c e m a y b e s u b s t a n t i a l l y r e d u c e d b y i n t r o d u c i n g a b s o r p t i v e m a t e r i a l s u c h a s m i n e r a l w o o l .

The typical frarne wall is another example of a cavity wall, a n d a l l t h e a b o v e c o n s i d e r a t i o n s a p p l y . T h e o v e r a l l p e r f o r m a n c e depends on the weights of the surface layers and the coupling through t h e a i r s p a c e o r t h r o u g h t h e s t u d s , w h i c h e v e r i s t h e m o r e i m p o r t a n t . U s u a l l y t h e t h r e e f a c t o r s a r e n o t i n d e p e n d e n t , a n d i t i s d i f f i c u l t t o p r e s e n t a s i m p l e a n a l y s i s . G e n e r a 1 l y , i n c r e a s i n g t h e m a s s o f t h e s u r f a c e l a y e r s r e d u c e s a i r - s p a c e t r a n s r n i s s i o n , b u t i n c r e a s i n g t h e i r s t i f f n e s s i n c r e a s e s s t u d t r a n s m i s s i o n ; m i n e r a l w o o l i n t h e s p a c e r e d u c e s a i r t r a n s m i s s i o n ; r e s i l i e n t c o n n e c t o r s o r s e p a r a t e s t u d s r e d u c e s t u d t r a n s m i s s i o n . T h e o v e r a l l p e r f o r m a n c e r n a y d e p e n d in a corylplicated way on each factor.

- 1 l

In walls with a positive break in the sound travel path, s u c h a s w i t h s t a g g e r e d s t u d s , t h e s o u n d r e s i s t a n c e c a n b e i m p r o v e d b y i n s t a l l i n g a s o u n d a b s o r b i n g m a t e r i a l s u c h a s m i n e r a l w o o l i n t h e s p a c e . S o u n d r e s i s t a n c e i s i m p r o v e d b e c a u s e t h e t r a n s m i s s i o n f r o r n o n e s i d e o f t h e w a l l t o t h e other is through the air space and not through the structure its elf.

T h u s , t h e f a c t o r s t h a t a f f e c t t h e s o u n d t r a n s m i s s i o n o f a w a I I a r e t h e m a s s o f t h e w a l l , t h e s t i f f n e s s , t h e c o n t i n u i t y of the sound transmission path through the wall, and in some c a s e s t h e s o u n d a b s o r p t i o n w i t h i n t h e s p a c e .

S o m e ' I y p i c a I C o n s t r u c t i o n s

T h e s i g n i f i c a n c e o f t h e s e f a c t o r s c a n b e b e t t e r appreciated by an examination of the constructions shown i n F i g u r e 1 0 . T o s i m p l i f y c o r n p a r i s o n , *-ir,. gypsurn w a l l b o a r d h a s b e e n a s s u m e d t h r o u g h o u t . T h e S T C v a l u e s given in this figure are typical numbers only and can vaty w i t h i n d i v i d u a l t e s t s .

T h e s i m p l e s t w a I I w i t h w o o d s t u d s a t 1 6 i n . c e n t r e s a n d I / Z t t p l a s t e r b o a r d o n e a c h s i d e h a s t h e l o w e s t r a t i n g - S T C 3 3 . When this wall is constructed with staggered studs on a 6 in. plate S T C 4 0 i s a c h i e v e d . H e r e t h e i n c r e a s e d a i r v o l u m e ( a n d r e d u c e d a i r c o u p l i n g ) i s h e l p f u l . W h e n m i n e r a l w o o l i s i n t r o d u c e d t h e d i s t i n c t i o n s b e t w e e n s t u d s y s t e m s b e c o r n e m o r e o b v i o u s . T h u s , w i t h s t u d s a t l 6 i n . c e n t r e s t h e i r n p r o v e m e n t i s o n l y f r o m S T C 3 3 t o 3 6 , w h e r e a s w i t h s t a g g e r e d s t u d s t h e i m p r o v e m e n t i s f r o r n S T C 4 0 t o 4 8 " T h i s e f f e c t i s e v e n m o r e p r o n o u n c e d w i t h t h i c k e r s u r f a c e s s i n c e i n t h e s e c a s e s t h e d e g r e e o f s t u d c o u p l i n g b e c o r n e s r n o r e i m p o r t a n t . S t u d c o u p l i n g c a n a l s o b e r e d u c e d b y u s i n g f e w e r s t u d s ( w o o d s t u d s a t 2 4 i n " c e n t r e s ) , o r more flexible ones (steel channels) o r b y i n t e r p o s i n g s o f t o r r e s i l i e n t l i n k s b e t w e e n s t u d a n d p l a s t e r b o a r d . D o u b l i n g t h e w e i g h t o f t h e s u r f a c e s ( l a t h a n d p l a s t e r o r d o u b l e l a y e r s o f p l a s t e r b o a r d ) i r n p r o v e s t h e p e r f o r m a n c e b y a b o u t 3 d B . R e s i d e n t i a l S t a n d a r d s r e q u i r e w a l l s b e t w e e n o c c u p a n c i e s t o h a v e a n S T C 4 5 a n d a l s o t o p r o v i d e a I - h r f i r e r e s i s t a n c e . W o o d - f r a m e w a l l s m e e t i n g t h e s e r e q u i r e r n e n t s a r e s h o w n i n F i g u r e I 1 .

The diagrarn on the right shows the most cornrnonly used arrangetnent of staggeted studs. In this case lath and p l a s t e r f i n i s h p r o v i d e s t h e r e q u i r e d s o u n d a n d f i r e r a t i n g without the addition of insulation. The wall with S/S -in. d r y w a l l r e q u i r e s i n s u l a t i o n i n t h e c a v i t y t o s a t i s f y t h e r e q u i r e m e n t o f S T C 4 5 . T h i s a p p l i e s a l s o t o t h e d i a g r a m

- L Z

on the left which shows resilient clips or channels, Lath and plaster finish will give an STC 45 without insulation whereas the wall with 5/8 -in. wallboard requires insulation to obtain this value. A n S T C 4 5 w a l l h a s b e e n c r i t i c i z e d a s b e i n g t o o l o w a n d n o t p r o v i d i n g a s h i g h a s t a n d a r d o f s o u n d r e s i s t a n c e a s m a n y p e o p l e w o u l d d e s i r e . A n S T C 5 0 w a l l w o u l d p r o v i d e a s i g n i f i c a n t i n c r e a s e i n o c c u p a n t s a t i s f a c t i o n a n d c a n b e o b t a i n e d w i t h a r e l a t i v e l y m o d e s t i n c r e a s e i n c o s t .

Two exarnples of wood-frame walls which give STC 50 a n d a l s o p r o v i d e a l - h r f i r e r a t i n g a r e s h o w n i n F i g u r e 1 2 . A g a i n t h e s e i n v o l v e a s t a g g e r e d s t u d w a l l a n d a w a l l u s i n g r e s i l i e n t m o u n t i n g s . T h e d i f f e r e n c e s b e t w e e n t h e s e w a l l s a n d t h o s e i n F i g u r e 1 l a r e t h a t j - i " . l a t h i s u s e d i n s t e a d o f . 3 / 8 - i n . l a t h f o r t h e p l a s t e r e d w a I I a n d t w o l a y e r s o f 3 / 8 - i n . g y p s u r n b o a r d a r e u s e d i n p l a c e o f a s i n g l e l a y e r o f . 5 / 8 - i . n . b o a r d f o r t h e d r y w a l l . I n b o t h c a s e s i n s u l a t i o n i s r e q u i r e d b e t w e e n t h e s t u d s . T u r n i n g n o w t o m a s o n r y w a l l s , c o n s t r u c t i o n s p r o v i d i n g S T C 4 5 a n d a I - h r f i r e r a t i n g a r e i l l u s t r a t e d i n F i g u r e I 3 . T h e s e i n c l u d e w a l l s c o n s t r u c t e d f r o m 8 - i n . d e n s e c o n c r e t e b l o c k o r 4 - i n . b l o c k w i t h p l a s t e r o n b o t h s i d e s . I f l i g h t w e i g h t b l o c k s a r e u s e d , 8 - i n . b l o c k s m u s t have the surfaces sealed by painting both sides or by applying a c o a t o f p l a s t e r o n a t l e a s t o n e s i d e . O t h e r w i s e t h e r e i s sound leakage through the pores, and the wall will not meet the STC 45 requirement. Alternatively, the application of a s e p a r a t e w a l l f i n i s h o v e r f u r r i n g w i l l p r o v i d e t h e n e c e s s a r y s e a l .

M a s o n r y c o n s t r u c t i o n s p r o v i d i n g S T C 5 0 a r e i l l u s t r a t e d in Figure 14. The top diagrarn illustrates a cavity wall which u t i l i z e s b o t h m a s s a s w e l l a s d i s c o n t i n u i t y o f t h e s o u n d t r a v e l p a t h t o r e d u c e s o u n d t r a n s m i s s i o n . I n t h e c a s e o f s o l i d m a s o n r y with the plaster or drywall finish attached by resilient fasteners the concrete block need only be 6 in. thick if made with dense

aggregate and 8 in. thick when cinder aggregate is used. If r e s i l i e n t f a s t e n e r s a r e n o t u s e d a n d t h e f i n i s h i s a p p l i e d o v e r f u r r i n g a n 8 - i n . d e n s e a g g r e g a t e b l o c k w i l l p r o v i d e a n S T C 5 0 r a t i n g .

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SOUND TRANSMiSSION THROUGH FLOORS

T h e p r i n c i p l e s d e s c r i b e d f o r w a l l s a l s o a p p l y t o f l o o r s a s f a r a s a i r b o r n e s o u n d i s c o n c e r n e d . A s h a s b e e n e x p l a i n e d t h e f a c t o r s t h a t d e t e r m i n e a i r b o r n e s o u n d r e s i s t a n c e a t e w e i g h t , s t i f f n e s s , b r e a k s i n s o u n d t r a v e l p a t h s , a n d s o u n d a b s o r p t i o n w i t h i n t h e s p a c e . T r a n s m i s s i o n o f i r n p a c t s o u n d t h r o u g h f l o o r s i s a n a d d i t i o n a l p r o b l e m a n d r e s u l t s w h e n t h e f l o o r i s s e t i n v i b r a t i o n t h r o u g h d i r e c t m e c h a n i c a l c o n t a c t . T h i s n o i s e i s t r a n s m i t t e d t h r o u g h t h e f l o o r s t r u c t u r e a n d r a d i a t e d t o t h e r o o r r l b e l o w . This type of noise can lead to rnore cornplaints than airborne s o u n d . I n t h i s c o u n t r y t h e r e a r e a s y e t n o e s t a b l i s h e d b u i l d i n g regulations governing impact noise transmission although the R e s i d e n t i a l S t a n d a r d s d o p r o v i d e a g u i d e f o r r a t i n g t h e i m p a c t n o i s e r e s i s t a n c e o f a n u m b e r o f f l o o r c o n s t r u c t i o n s .

T h e m o s t e f f e c t i v e m e t h o d o f r e d u c i n g i r n p a c t n o i s e t r a n s m i s s i o n i s b y t h e u s e o f a s o f t f l o o r c o v e r i n g s u c h a s a c a r p e t a n d p a d . C o r k t i l e i s a l s o o f v a l u e b u t i s l e s s effective than a carpet. Other so-called resilient floor c o v e r i n g s s u c h a s v i n y l , I i n o l e u m , o r r u b b e r t i l e a r e o f Iittle value in controlling impact noise. Another method of c o n t r o l i s t o p r o v i d e a f l o a t i n g f l o o r s u r f a c e . T h i s c a n b e d o n e b y s e p a r a t i n g t h e f i n i s h f l o o r f r o m t h e f l o o r s t r u c t u r e b y m e a n s o f a r e s i l i e n t l a y e r s u c h a s f i b r e b o a r d , S i m i l a r l y t h e c e i l i n g r n a y b e s u s p e n d e d b y t h e u s e o f r e s i l i e n t c l i p s w h i c h p a r t i a l l y i s o l a t e t h e c e i l i n g f r o m t h e f l o o r s t r u c t u r e . A l t e r n a t i v e l y , t h e c e i l i n g r n a y b e s u p p o r t e d b y a s e t o f j o i s t s s e p a r a t e f r o m t h o s e s u p p o r t i n g t h e f l o o r . T h i s p r o v i d e s i n e f f e c t a s i t u a t i o n m u c h l i k e t h e s t a g g e r e d s t u d a r r a n g e m e n t . With such constructions sorne further reduction in impact n o i s e t r a n s m i s s i o n c a n b e a c h i e v e d b y p l a c i n g a s o u n d a b s o r b i n g l a y e r o f m i n e r a l w o o l i n s u l a t i o n w i t h i n t h e j o i s t s P a c e " S o m e T y p i c a l C o n s t r u c t i o n s T h e v a r i o u s m e t h o d s u s e d i n r e d u c i n g i r n p a c t n o i s e t r a n s r n i s s i o n a r e i l l u s t r a t e d i n F i g u r e 1 5 . A g a i n , f o r e a s e o f c o m p a r i s o n , a c e i l i n g f i n i s h o f ) - i n . g y p s u r n b o a r d i s u s e d t h r o u g h o u t . T h e f i n i s h f l o o r c o n s i s t s o f j - i n . h a r d w o o d o n a * - i " . s u b f l o o r .

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A s i n d i c a t e d i n t h e u p p e r l e f t d i a g r a m o f F i g u r e l 5 a s i r n p l e w o o d j o i s t f l o o r s y s t e m h a s a n i m p a c t n o i s e r a t i n g or INR of -18. As e><plained previously, an INR of less than - 1 0 i s c o n s i d e r e d p o o r , a r a t i n g b e t w e e n - 1 0 t o z e r o i s o n l y f a i r , a n d a r a t i n g o f z e r o o r o v e r i s g o o d . T h e S T C o f t h i s particular system is 32. If the ceiling finish in this construction w a s o m i t t e d , a s i n t h e c a s e o f a n u n f i n i s h e d b a s e m e n t , t h e S T C w o u l d b e r e d u c e d t o 2 5 a n d t h e I N R t o - 2 8 .

By p"oviding a floating floor as shown in the lower l e f t d i a g r a m ( F i g u r e l 5 ) t h e S T C i s r a i s e d f r o r n 3 2 t o 4 6 a r . d t h e I N R i n c r e a s e d f r o m - l B t o a b o u t - 9 " T h e f l o a t i n g f l o o r i s f o r m e d b y p l a c i n g a l a y e r o f f i b r e b o a r d o v e r t h e s u b f l o o r , gluing strapping to the fibreboard and installing another sub-floor and finish sub-floor on this strapping. About the same i m p r o v e m e n t i n S T C a n d i n I N R c a n b e a c h i e v e d b y p r o v i d i n g a r e s i l i e n t m o u n t i n g f o r t h e c e i l i n g o r b y s t a g g e r i n g t h e j o i s t s a s i n d i c a t e d i n t h e d i a g r a m s o n t h e r i g h t ( F i g u r e 1 5 ) .

Batt-type insulation within the joist space would improve t h e p e r f o r r n a n c e o f a l l t h e s e s y s t e m s t o s o m e e x t e n t w i t h r e s p e c t t o b o t h a i r b o r n e a n d i m p a c t n o i s e . T h e m o s t n o t i c e a b l e e f f e c t w o u l d b e a c h i e v e d w i t h t h e s u s p e n d e d c e i l i n g a n d s t a g g e r e d j o i s t s y s t e m s . A d d i n g a c a r p e t a n d p a d t o a n y o f t h e s e c o n s t r u c t i o n s w o u l d a l s o c o n s i d e r a b l y i m p r o v e t h e i m p a c t r a t i n g . W h e n s e p a r a t i n g d w e l l i n g u n i t s b y s o u n d - r e s i s t a n t f l o o r s , f i r e a s p e c t s a l s o s h o u l d b e c o n s i d e r e d . F i g u r e l 5 i l l u s t r a t e s s o m e t y p i c a l w o o d f l o o r s y s t e m s t h a t p r o v i d e a 1 - h r f i r e s e p a r a t i o n a n d a l s o g i v e S T C 4 5 . T h e s e p r o v i d e a f a i r I N R r a t i n g o f b e t w e e n - 1 0 a n d z e r o . A s c a n b e s e e n t h e s e d i a g r a r n s a r e q u i t e s i m i l a r t o t h o s e i n F i g u r e 1 5 e x c e p t t h a t S / e - t n . f i r e - r e s i s t a n t g y p s u r n b o a r d o r l a t h a n d p l a s t e r h a v e b e e n u s e d f o r t h e c e i l i n g f i n i s h . T h e l a t h a n d p l a s t e r w i l l h a v e s u p e r i o r s o u n d r e s i s t a n c e t o tine 5/B-tn" wallboard. A s m e n t i o n e d p r e v i o u s l y , S T C 4 5 i s a m i n i r n u m s t a n d a r d a n d i t i s o f t e n d e s i r a b l e t o p r o v i d e S T C 5 0 t o a c h i e v e a h i g h e r p e r c e n t a g e o f o c c u p a n t s a t i s f a c t i o n . I n t h e c a s e o f f l o o r s , h o w e v e r , o c c u p a n t s a t i s f a c t i o n a l s o d e p e n d s o n g o o d i m p a c t r e s i s t a n c e , a n d this will require a construction having an INR of zeto or greater.

- t 5 F i g u r e 1 7 i l l u s t r a t e s t w o f l o o r c o n s t r u c t i o n s t h a t p r o v i d e S T C 5 0 o r b e t t e r a n d a t t h e s a m e t i m e p r o v i d e g o o d i m p a c t n o i s e r e s i s t a n c e . I n t h e s e c o n s t r u c t i o n s a f l o a t i n g f l o o r i s c o m b i n e d w i t h a s u s p e n d e d c e i l i n g o r s t a g g e r e d j o i s t s t o a c h i e v e t h e d e s i r e d r e s u l t . I n a d d i t i o n , i n s u l a t i o n h a s b e e n a d d e d b e t w e e n t h e j o i s t s t o i m p r o v e p e r f o r m a n c e . T u r n i n g t o n o n c o m b u s t i b l e c o n s t r u c t i o n , F i g u r e 1 8 i l l u s t r a t e s t h r e e c o m m o n c o n s t r u c t i o n s o f t h i s t y p e w h i c h w i l l p r o v i d e S T C 4 5 w i t h a f a i r r e s i s t a n c e t o i m p a c t n o i s e . W i t h t h e s i m p l e c o n c r e t e s l a b f l o o r i t i s n e c e s s a r y t o i n s t a l l s o m e t y p e o f s o f t f l o o r c o v e r i n g o n t h e s l a b ( u p p e r d i a g r a r n ) or provide a resilient Layer between the slab and the finish f l o o r ( m i d d l e d i a g r a m ) t o a c h i e v e a f a i r i m p a c t r a t i n g . A c a r p e t c o m b i n e d w i t h a r e s i l i e n t p a d d i r e c t l y o n t h e s l a b w o u l d p r o v i d e g o o d i m p a c t r e s i s t a n c e . T h e l o w e r d i a g r a m i n F i g u r e 1 8 i l l u s t r a t e s a n o t h e r n o n c o m b u s t i b l e f l o o r u s i n g b a r j o i s t s . H e r e a g a i n , t o a c h i e v e a f a i r r e s i s t a n c e t o i m p a c t n o i s e , e i t h e r a s o f t s u r f a c e r n u s t b e p r o v i d e d o r a r e s i l i e n t l a y e r p r o v i d e d b e t w e e n t h e f l o o r f i n i s h a n d t h e s l a b . T h e 5 / 8 - i n . f i r e - r e s i s t a n t g y p s u m b o a r d o n t h e c e i l i n g w i l l p r o v i d e a c o n s t r u c t i o n h a v i n g a I - h r f i r e r e s i s t a n c e . F i g u r e 1 9 s h o w s t h r e e f l o o r s t h a t w i l l p r o v i d e g o o d i m p a c t n o i s e r e s i s t a n c e a n d S T C 5 0 o r o v e r . T h e s l a b ( u p p e r d i a g r a m ) h a s b e e n i n c r e a s e d t o a 5 - i n . t h i c k n e s s c o m p a r e d w i t h 3 i n . i n F i g u r e 1 8 . A c a r p e t a n d p a d w o u l d s t i l l b e n e c e s s a r y t o o b t a i n a g o o d i m p a c t r a t i n g . A l t e r n a t i v e l y , t h e f i n i s h f l o o r c a n b e s u p p o r t e d o n f u r r i n g s t r i p s c e m e n t e d t o t h e s l a b a s s h o w n i n t h e m i d d l e d i a g r a m . T h e f i n i s h i n t h i s c a s e c o u l d b e t i l e o n e r ]-in. underlay supported by a subfloor.

T h e l o w e r d i a g r a r n i n d i c a t e s a b a r j o i s t s y s t e m i n w h i c h t h e c e i l i n g f i n i s h i s s u p p o r t e d o n r e s i l i e n t c l i p s t o o b t a i n a g o o d impact rating. In addition, mineral wool rnust be installed in t h e j o i s t s p a c e w h e n a d r y w a l l c e i l i n g i s u s e d . T h e a d d i t i o n o f a carpet and pad would further improve the irnpact rating.

I n s u m m a r y , t h e r n e t h o d s o f a c h i e v i n g c o n t r o l o f n o i s e t r a n s m i s s i o n t h r o u g h f l o o r s i n c l u d e p r o v i d i n g a r e s i l i e n t l a y e r between the finish floor and the floor structure, suspending t h e c e i l i n g o n r e s i l i e n t c l i p s o r c h a n n e l s , o r u s i n g s t a g g e r e d

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j o i s t s . _{T h e s e m e a s u r e s w i l l n o t o n l y r e d u c e a i r b o r n e n o i s e} transrnission but will improve impact perforrnance as well. T h e p r o v i s i o n o f a c a r p e t a n d p a d a d d s l i t t 1 e t o t h e r e s i s t a n c e to airborne noise but is very effective in improving the impact p e r f o r m a n c e .

NOISE IN MECHANICAL SYSTEMS

M e t h o d s o f n o i s e c o n t r o l i n p l u m b i n g a n d h e a t i n g

systems are less weII established than the rnethods for control of airborne and impact sound through building elements,

S o m e g e n e r a l g u i d e l i n e s c a n b e l a i d d o w n , h o w e v e r , a n d t h e s e will be illustrated with examples from known trouble areas.

N o i s e f r o m m e c h a n i c a l s y s t e m s m a y b e e i t h e r v i b r a t i o n o r i r n p a c t n o i s e , o r a i r b o r n e n o i s e . T h e n o i s e r r t a y a r i s e within the mechanical equipment such as fans, motors, and pumps, or be generated by the flow of air in drrcts or the flow of water in pipes. In addition, the ducts themselves rnay act as a channel to transmit noise frorn one roorn to another. Equipment Noise

Equipment noise rnay be reduced in the following ways: l. Locate the equipment as far away as possible

from the quiet areas

C o n f i n e t h e n o i s e b y s u r r o u n d i n g t h e e q u i p m e n t w i t h s o u n d - r e s i s t i v e c o n s t r u c t i o n o r b y p r o v i d i n g b u f f e r z o n e s s u c b a s c o r r i d o r s ,

s t a i r w e l l s o r s t o r a g e r o o m s .

Line equipment enclosures with sound-absorbent m a t e r i a l s " S u c h t r e a t m e n t i s n o t a s u b s t i t u t e f o r s o u n d - r e s i s t i v e c o n s t r u c t i o n b u t w i l l h e l o b y r e d u c i n g t h e n o i s e l e v e l .

Look for rtquietn equipment and appliances. In the case of equipment this may mean a quieter

operating pump, or a motor that has been s p e c i f i c a l l y d e s i g n e d t o c o n t r o l v i b r a t i o n . S o m e a p p l i a n c e s s u c h a s d i s h w a s h e r s a n d g a r b a g e d i s p o s a l u n i t s a r e m a r k e t e d u n d e r s o - c a l l e d I t r e g u l a r t t o r l r q u i e t r t m o d e l s . 7.. 3 . 4.

T 7

I n a d d i t i o n , s o r n e w a t e r c l o s e t s o p e r a t e at a lower noise leve1 than others.

T o p r o v i d e a b a s i s f o r s e l e c t i o n , n o i s e level ratings should be obtained if available s o t h a t t h e p e r f o r m a n c e o f t h e d i f f e r e n t m o d e l s c a n b e c o m p a r e d .

Isolate the equipment from the structure b y s u p p o r t i n g o n r e s i l i e n t p a d s "

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

T h e s e l a s t t w o p r i n c i p l e s a r e i l l u s t r a t e d i n F i g u r e 2 0 . The upper figure shows a purnp on resilient pads and connected t o t h e c i r c u l a t i n g s y s t e m b y a l e n g t h o f f l e x i b l e h o s e . T h e l o w e r f i g u r e s h o w s a n e l e c t r i c a l a p p l i a n c e s u p p o r t e d o n r e s i l i e n t p a d s a n d w i r e d w i t h f l e x i b l e c a b l e t o p r e v e n t d i r e c t t r a n s m i s s i o n o f v i b r a t i o n t o t h e s t r u c t u r e . N o i s e i n P i p i n g N o i s e p r o b l e m s a l s o a r i s e f r o m w a t e r f l o w t h r o u g h piping. The turbulence of the flow creates whistling or

gurgling sounds and causes pipe vibration" Contraction and e x p a n s i o n o f p i p e s d u e t o t e r n p e r a t u r e c h a n g e s m a y c a u s e creaking at the supports.

Three significant factors that affect noise in plumbing s y s t e m s a r e t h e w a t e r p r e s s u r e , w a t e r v e l o c i t y , a n d t h e number of valves and fittings. For good noise control the s t a t i c w a t e r p r e s s u r e i n t h e s y s t e r n s h o u l d n o t e x c e e d 3 5 t o 4 5 p s i " I f i t i s r n o r e , a p r e s s u r e - r e g u l a t i n g v a l v e s h o u l d b e i n s t a l l e d . I n c r e a s i n g t h e d i a m e t e r o f t h e s u p p l y p i p i n g will also reduce the velocity but this is less effective than r e d u c i n g t h e p r e s s u r e t o c o n t r o l n o i s e i n p i p e s .

Owing to water turbulence, valves and fittings can p r o d u c e c o n s i d e r a b l y m o r e n o i s e t h a n s t r a i g h t r u n s o f p i p e . T e s t s o n |-in. steel pipe have shown that valves can produce n o i s e l e v e l s v a r y i n g f r o m Z 0 t o 3 0 d B d e p e n d i n g o n t h e t l p e of valve and whether or not it is fully open. Sirnilar noise l e v e l s a r i s e w i t h m e t e r s a n d o t h e r f i t t i n g s t h a t c r e a t e s o m e discontinuity of flow within the 1ine. Globe valves are

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

5 .

- l 8

if valves are to remain fully open rnost of the time a gate valve is quieter. In general the fittings in the system should be kept few in number by designing the layout with a minimum o f b e n d s .

Piping must be isolated frorn the building structure t o c o n t r o l t h e t r a n s m i s s i o n o f n o i s e o r i g i n a t i n g i n t h e s y s t e m . \ M h e n p i p e s a r e r i g i d l y a t t a c h e d t o a l a r g e s u r f a c e b y h a n g e r s , c l i p s o r s t r a p s , t h e w h o l e s u r f a c e w i l l r a d i a t e s o u n d a n d g e n e r a t e n o i s e t h r o u g h o u t t h e s t r u c t u r e . A l a y e r o f r e s i l i e n t m a t e r i a l b e t w e e n t h e s u p p o r t a n d t h e p i p e w i l l g r e a t l y r e d u c e t r a n s m i s s i o n o f n o i s e i n t h i s w a y . T h e n u m b e r o f p i p e s u p p o r t s

should be kept to a rninimum and the straps or hangers attached t o t h e m o s t m a s s i v e s t r u c t u r a l e l e m e n t a v a i l a b l e . I t i s b e t t e r , f o r e x a m p l e , t o f a s t e n t o r n a s o n r y w a l l s t h a n t o f l o o r j o i s t s . It is most important to avoid fastening to light panel surfaces which will readily amplify the sound.

A frequent source of noise is the flow of waste water from a water closet or bathtub. As a first step in the control of this problem the drain piping should be kept away frorn walls o f q u i e t a r e a s s u c h a s b e d r o o m s . S e c o n d l y , w h e r e v e r t h e p i p e p a s s e s t h r o u g h o r i s a t t a c h e d t o t h e b u i l d i n g s t r u c t u r e , r e s i l i e n t m a t e r i a l s h o u l d b e u s e d t o p r e v e n t d i r e c t c o n t a c t ( F i g u r e 2 L ) . A resilient mounting should be used to support the pipe at the

end of a long vertical run as indicated in the bottom diagram o f F i g u r e 2 1 " T h i s i s o f p a r t i c u l a r i m p o r t a n c e i n m u l t i - s t o r e y b u i l d i n g s w h e r e t h e u s e o f r e s i l i e n t s u p p o r t s f o r p l u m b i n g s t a c k s w i l l d o m u c h t o r e d u c e i r n p a c t s o u n d t r a n s m i s s i o n ,

R e s i l i e n t m a t e r i a l a t t h e s u p p o r t s w i l l a l s o p e r m i t hot water piping to rnove without binding due to expansion and c o n t r a c t i o n . T e r n p e r a t u r e d i f f e r e n c e s o f I 0 0 ' F m a y o c c u r in these lines causing copper piping to expand or contract as much as I in" in an 80-ft run. To allow for this rnovement, swing arm offsets or loops should be provided in all long straight runs of piping. Insulating the pipe will help to

maintain a more even temperature in the Pipe, thus minirnizing e>cpansion and contraction.

Another problem with piping is water hammer. This occurs when water is turned on and off quickly, producing a s h o c k w a v e i n t h e s y s t e m w h i c h c a u s e s t h e p i p e t o v i b r a t e .

_ L 9 H i g h p r e s s u r e , h i g h v e l o c i t y , a n d q u i c k c l o s i n g v a l v e s c o m b i n e t o p r o d u c e t h e w o r s t w a t e r h a m m e r c o n d i t i o n s . T h e p r o b l e r n c a n b e p a r t i c u l a r l y s e v e r e i n e q u i p m e n t , s u c h a s a u t o r n a t i c w a s h e r s , t h a t u s e e l e c t r i c a l m e a n s o f s h u t - o f f . W a t e r h a m m e r c a n b e c o n t r o l l e d b y i n s t a l l i n g a i r c u s h i o n s t o a c t a s s h o c k a b s o r b e r s i n t h e s y s t e m ( F i g u r e Z Z ) . T h e s e r n a y e v e n t u a l l y I o s e t h e i r e f f e c t i v e n e s s a s t h e a i r i n t h e m b e c o r n e s a b s o r b e d i n t h e w a t e r . T h e s y s t e m m u s t t h e n b e d r a i n e d t o l e t a i r b a c k i n . S p e c i a l a i r c h a m b e r s a r e a v a i l a b l e w i t h a d i a p h r a g m t o p r e v e n t t h e i r b e c o m i n g w a t e r - I o g g e d . b y : I n s u m m a r y , n o i s e i n p i p i n g s y s t e m s c a n b e c o n t r o l l e d 1 . R e d u c i n g w a t e r p r e s s u r e Z " I n c r e a s i n g t h e s i z e o f p i p i n g M i n i m i z i n g t h e u s e o f f i t t i n g s , p a r t i c u l a r l y q u i c k - c l o s i n g v a l v e s Isolating pipes and fixtur es frorn

t h e s t r u c t u r e w i t h r e s i l i e n t ' o a d s Keeping drain pipes away from walls

o f q u i e t a r e a s

P r o v i d i n g a i r c u s h i o n s t o c o n t r o l rn'ater hamrner

M a k i n g p r o v i s i o n f o r m o v e m e n t d u e t o expansion and contraction

N o i s e i n D u c t s

D u c t w o r k c a n a l s o g i v e r i s e t o n o i s e p r o b l e m s " A rnetal duct acts like a speaking tube on a ship and readily t r a n s f e r s s o u n d f r o r n o n e a r e a t o a n o t h e r . T h i s c a n l e a d t o a n n o y i n g n o i s e p r o b l e r n s t h r o u g h t h e s h o r t - c i r c u i t i n g o f s o u n d b a r r i e r s b e t w e e n a p a r t m e n t s a n d t h r o u g h t h e t r a n s f e r of equipment noise throughout the living space. Sound does not only enter or leave a metal duct through an opening or g r i l l e b u t c a n a l s o e n t e r t h r o u g h t h e t h i n r n e t a l s i d e s ( F i g u r e Z 3 ) . 3 . 4. 5 . 6 . 7 .

- 2 0 T h i s i s w h y d u c t s t h r o u g h s o u n d b a r r i e r s s h o u l d b e k e p t t o a m i n i m u m a n d d u c t l a y o u t t h r o u g h n o i s y a r e a s s u c h a s s e r v i c e o r m a i n t e n a n c e r o o m s s h o u l d b e a v o i d e d i f p o s s i b l e . S u c h r r r e a s L r r e s w i l l h e l p t o r e d u c e n o i s e p i c k - u p b y t h e d u c t s . F i b r o u s l i n i n g s i n s i d e t h e d u c t s w i l l r e d u c e s o u n d t r a n s m i s s i o n w i t h i n a d u c t s y s t e r n . A 6 - f t l e n g t h n e x t t o e a c h w a l l o r c e i l i n g o u t l e t i s g e n e r a l l y s u f f i c i e n t . T h i s c a n be of particular value in cornmon duct exhausts from kitchens o r b a t h r o o m s o f a p a r t m e n t s w h i c h p r o v i d e a n e a s y p a t h f o r n o i s e t r a n s m i s s i o n . N o t e , h o u . e v e r , t h a t i n s u l a t i o n o n t h e o u t s i d e o f a d u c t d o e s n o t h e l p i n c o n t r o l l i n g a i r b o r n e t r a n s -m i s s i o n t h r o u g h t h e d u c t . W h e n n o i s e i s c a u s e d b y a i r f l o w , s t r e a m l i n i n g t h e d u c t w o r k u s i n g s m o o t h c u r v e b e n d s o r t u r n i n g v a n e s i n e l b o w o r r r T i l f i t t i n g s w i l l r e d u c e t h e n o i s e l e v e l b y r e d u c i n g t u r b u l e n c e . F i g u r e Z 4 i l l u s t r a t e s t h e u s e o f f l e x i b l e c o l l a r s t o p r e v e n t t r a n s f e r o f e q u i p m e n t v i b r a t i o n t o t h e d u c t w o r k . N o t e t h a t t h e r e i s n o a t t a c h r n e n t t o t h e s t r u c t u r e b e t w e e n the flexible connection and the equipment. The supporting h a n g e r s s h o u l d n o t b e p l a c e d b e t w e e n t h e f l e x i b l e c o l l a r a n d t h e e q u i p m e n t i t i s s u p p o s e d t o i s o l a t e . O n e o f t h e b i g g e s t o b s t a c l e s t o s u c c e s s f u l n o i s e c o n t r o l s t i 1 l r e r n a i n s - p o o r c o n s t r u c t i o n p r a c t i c e " I t i s n o t e n o u g h t o m e r e l y s p e c i f y p r o p e r n o i s e c o n t r o l m e t h o d s s u p e r v i s i o n m u s t b e p r o v i d e d t o e n s u r e g o o d w o r k m a n s h i p a n d c o n t r o l o f c o n s t r u c t i o n d e t a i l s . E v e n r n i . n o r v a r i a t i o n s f r o m s p e c i f i e d m e t h o d s c a n n u l l i f y t h e v a l u e o f s o u n d c o n d i t i o n i n g b y p e r m i t t i n g d u c t s , p i p e s , o r c o n d u i t s t o s h o r t - c i r c u i t c o n s t r u c t i o n s e p a r a t i o n s . C O N S T R U C T I O N P R A C T I C E S T H A T D E C R E A S E S O U N D R E S I S T A N C E T h e S T C a n d I N R r a t i n g s f o r w a l l s a n d f l o o r s t h a t w e r e r n e n t i o n e d e a r l i e r w e r e d e t e r r n i n e d i n a l a b o r a t o r y u n d e r s o r n e -w h a t a r t i f i c i a l c o n d i t i o n s i n t h a t t h e s p e c i r n e n s -w e r e c a r e f u l l y c o n s t r u c t e d a n d n o e x t r a n e o u s t r a n s m i s s i o n p a t h s w e r e i n v o l v e d " Such values rnay be obtained in the field, but only when equal c a r e i s t a k e n a n d t h e r e a r e n o l e a k a g e o r f l a n k i n g t r a n s m i s s i o n p r o b l e m s . S o m e d e p a r t u r e f r o r n t h e t e s t e d c o n s t r u c t i o n m a y b e i n e v i t a b l e , b u t i n r n a n y i n s t a n c e s t h e r e i s a n u n n e c e s s a r y T e d u c t i o n i n p e r f o r r n a n c e b e c a u s e o f p o o r c o n s t r u c t i o n p r a c t i c e .