Sound insulation in wood-framed buildings: focus on systems performance

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Sound insulation in wood-framed buildings: focus on systems performance

Sound isolation in wood-framed buildings:

Focus on System Performance

David Quirt and Trevor Nightingale Wood Solutions, November 2007

This talk considers …

• Concepts and terminology

• Technical standards and the Building Code • Construction details that affect transmission

• Using the results of extensive testing to create a Design Guide for wood framed construction

• Based on consortium projects supported by:

Canada Mortgage & Housing (CMHC), TrusJoist, Forintek Canada, Marriott International, NRC, Owens Corning, USG

Building Code Requirements (pre-2005)

This requirement in National Building Code reflects the technology that was available in the 1970’s when it was written.

. . . a dwelling unit shall be separated from every other space in the building in which noise may be generated by construction providing a sound transmission class rating not less than 50. . .

Transmission through wall Airborne Sound Source Assumes

noise problem = bad wall

• Focus is just on the separating assembly

• Design by requirement for separating assembly:

• laboratory STC

• in situ (field) FSTC

The old simple way …

• Works fairly well for low sound insulation (STC under 45)

• When the design goal is above STC 45,

the overall sound insulation is usually worse (and sometimes much worse) than the

STC rating of the separating wall or floor.

• First reaction is to blame separating wall or floor (or the people who built it)

Transmission paths in real building

Flanking Transmission via ceiling surfaces Transmission through wall Airborne Sound Source Flanking Transmission via floor surfaces

Objective is sound insulation

for occupants (including all paths) Ö Design process must deal

It’s like dealing with thermal insulation…

• Heat doesn’t just escape through the roof

• Good design includes R-value for walls, windows, etc. • With good insulation of the basic assemblies,

then air leakage and other short circuits matter

• Sound (or vibro-acoustic energy) is the same …

– First, you have to use a good separating assembly – But then, you also have to deal with the other

Describing system performance

Flanking Transmission via ceiling surfaces Direct Transmission through wall Airborne Sound Source Flanking Transmission via floor surfaces

Ö ASTC (Apparent STC) includes all transmission paths between two rooms

Intent of 2005 National Building Code …

An objective of this Code is:

“to limit the probability that, as a result of the

design or construction of the building, a person in the building will be exposed to [unacceptably high] levels of sound originating in adjacent spaces.… Focus is on sound heard by occupant of a dwelling

Ö technical requirement should use

Apparent STC (including all paths in a building)

• Unfortunately these definition clarifications in ASTM E336 were not accepted until 2005 (well after the 2005 NBCC was finalized).

This talk is not about the Building Code…

• The Codes revision process is underway

• Most builders want to achieve the best results possible for the money they are spending.

• Focus of this talk is good practice –

the technology needed for acoustical design that efficiently meets appropriate objectives

This talk will consider:

• Performance of some typical constructions • Breaking this down into transmission paths • Putting these together in a design framework

For simplicity, I will focus:

• Just airborne sound (voices, etc.) • Just for side-by-side units

For some typical constructions:

• What ASTC is achieved?

• What transmission paths matter?

Two side-by side rooms :

Start with just:

• The separating wall

• The floor/ceiling assembly

Apparent STC 46 to 48 STC 55 Direct Transmission Flanking via subfloor

Floor joists parallel to separating wall

(non-loadbearing wall)

STC 52 Apparent STC 44 to 45 Alternate junction details Direct Transmission Flanking via subfloor

Floor joists parallel to separating wall

(non-loadbearing wall)

STC 52 Apparent STC 42 Floor joists perpendicular to separating wall (loadbearing wall) Direct Transmission Flanking via subfloor & joists

STC 57

Apparent STC 43

Add more gypsum board to wall surfaces

Direct Transmission

Flanking via subfloor & joists

STC 70

Apparent STC 43

Add high performance panels to wall surfaces

Direct Transmission

Flanking via subfloor & joists

Apparent STC 50 (with OSB) 56 (concrete + resilient mat) STC 57 Direct Transmission Changed flanking via floor surfaces

Topping over the subfloor changes flanking transmission (Various toppings)

Ratings for transmission paths

Next, describe the typical path attenuations with more technical detail

• First consider some cases with just the separating wall and the floor

• Then add other significant paths:

– Side walls

Just the floor-floor

path

Floor-floor paths vs. separating wall

for Specific Paths, dB

Joists צ wall, Path ASTC = 48 Joists ٣ wall, Path ASTC = 45

Joists ٣ across wall, Path ASTC = 39 Floor-Floor Paths (Bare Floor)

(Reference curve)

Improve floor-floor path with topping

for specific paths, dB

(Reference curve)

Direct path through wall Path ASTC = 52

Joists צ wall, Path ASTC = 58 Joists ٣ wall, Path ASTC = 55

Floor-Floor Paths (Bonded Concrete Topping)

Putting it together –

Design Guideline Framework

• Four paths tend to be most significant:

– Direct transmission through separating wall – Floor-floor flanking path

– Side wall flanking path

– Ceiling-ceiling flanking path

• Which ones matter depends on the details

• Combining all paths gives overall sound transmission (and hence Apparent-STC)

Transmission paths in “apartments”

Flanking via floor surfaces

(Ceiling surfaces isolated)

Transmission through wall Airborne

Sound Source

Other paths of concern: 2 side walls

for Specific Paths, dB

(Reference curve) Direct path through wall

Path ASTC = 52 Sidewall path

(gypsum board direct-attached) Path ASTC = 61

Combining all paths for “apartments”

Separating wall: Basic Wall

(STC 52)

Better Wall (STC 57)

Side walls: Direct or

resilient Direct Resilient

Floor Surface: (Apparent–STC)

No topping (basic) 43 43 43 y y y y y y y y y y y y 38 mm gypsum concrete + resilient mat on subfloor 51 53 55

Transmission paths in “row housing”

Flanking via ceiling surfaces Transmission

through wall Airborne

Sound Source

Flanking via floor surfaces

Ceiling gypsum board screwed to joists

for Specific Paths, dB

Ceiling-ceiling path

(gypsum board direct-attached) Path ASTC = 52

(Reference curve) Direct path through wall

Combining all paths for “row housing”

Separating wall Basic Wall

(STC 52)

Better Wall (STC 57)

Side walls: Direct or

resilient Direct Resilient

Floor Surface: (Apparent–STC)

No topping (basic) 42 43 43 y y y y y y y y y y y y 38 mm gypsum concrete + resilient mat on subfloor 49 51 52

Slide 30

Summary

• Systematic study gave path attenuation terms for airborne and impact sources

– Depend on key construction details:

• Floor framing, toppings and covering • Wall framing, and gypsum board layers

• Manageable set of attenuation terms for each parameter allows estimation of specific design tradeoffs

Slide 31

Reports on website:

irc.nrc-cnrc.gc.ca/ircpubs/

Research Report 219

Guide for Sound Insulation in Wood Frame Construction (simplified design guide)