Technical Series 90-246
Sound transmission between floors is acommon problem in multiple-unit dwellings. To find effective and economical ways of resolving this problem, CMHC initiated aresearch project on the sound isolation provided by floor/ceiling assemblies in wood construction.The first phase of this study, described here, investigated the acoustical performance of different materials incorporated in the underside of floor/ceiling assemblies. These included sound absorptive materials in the floor cavity, as well as ceiling finishes and installation methods. The results of these tests are presented in the following table, which contains diagrams of the assemblies tested and their detailed composition, Sound Transmission Class (STC) ratings and Impact Insulation Class (JIC) ratings. The higher the STC andJIC rating, the better.
Spacing the joists at 406 mm (16 in.) centres seemed to generate a sub-panel resonance at 160 Hz in the plywood subfloor. In many floors tested, this effect reduced the STC rating.
The four different types of resilient furrings tested (floor 7) provided almost identical sound isolation performance.
Resilient furrings are highly recommended in the construction of floor/ceiling assemblies separating dwellings. The use of wood furrings is not advisable since the mechanical coupling they provided between the floor and the ceiling greatly reduced the performance of the assemblies tested.
Doubling the mass of a drywall ceiling attached to resilient furrings (floor 9) led to an improvement of roughly 5 dB in the STC rating and in the transmission loss at all frequencies. With wood furrings, doubling the mass ofthe drywall ceiling (floor 8) led to no improvement in either the STC rating or the transmission loss at low frequencies for which the mechanical coupling was important. It also led to adegradation in the IIC rating.
Filling the joist cavity provided approximately the same STC performance, regardless of the material used (floor 3, floor 11). Wood fibreboard is often inserted between the joists and resilient fumngs (floor 10). This practice did not provide any STC improvements.
The most efficient way of improving the performance of an existing floor/ceiling assemblyis to build an additional ceiling under it. A ceiling consisting of 12.7 mm (1/2 in.) drywall, fastened to 63.5 mm (2 1/2 in.) standard metal studs, with batt insulation between the studs (floor 5), provided the best results. It also improved the STC rating by 15 points.
The independently joisted floor/ceiling measured in this study (floor 12) tested STC 40, while more conventional floor/ceiling assemblies built with resilient furring tested around STC 45. The use of independentlyjoisted ceilings is therefore not recommended.
See also: Soundproofing Floors Phase II: The Surface of the Floor (90-247).
|1||BASIC FLOOR ASSEMBLY
|7A - Resilient furrings by Pichette Metal, at 610mm centres||44||43|
|7B - Resilient furrings by RL Metal, at 610 mm centres||44||43|
|7C - Resilient furrings by Trebord, at 610 mm centres||44||43|
|7D - Resilient furrings RC-1 by CCC, at 610 mm centres||45||44|
|7E - Resilient furrings RC-1 by CCC, at 406 mm centres||44||42|
|7F - Resilient furrings RC-1 by CCC, at 406 mm centres installed parallel to the joists||45||42|
|A -3 layers of 89 mm pink glass fibre batt insulation||51||46|
|B - Cellulose blown-in attic insulation: Weathershield by Thermo-Cell Insulation Ltd.||49||47|
|C - Acoustical blown-in insulation: Benocoustics by Benolec||51||47|
Research Project on the Noise Isolation Provided by Floor/Ceiling Assemblies in Wood Construction (Phase I)
MJM Acoustical Consultants Inc.
Under Part IX of the National Housing Act, the Government of Canada provides funds to CMHC to conduct research into the social, economic and technical aspects of housing and related fields, and to undertake the publishing and distribution of the results of this research.
For a complete listing of Research and Development Highlights, or for more information on CMHC housing research, please contact:
The Canadian Housing Information CentreCanada Mortgage and Housing Corporation
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