Research Highlights

Technical Series 90-246

Soundproofing Floors Phase 1: The Underside of the Floor

Introduction

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.

Findings

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).

Floor Diagram Composition Sound
Transmission
Class (STC)
Rating
Impact
Insulation
Class (IIC)
Rating
1 cross-section BASIC FLOOR ASSEMBLY
  • 16mm plywood
  • 38 mm x 230 mm joists at 406 mm centres
24 20
2 cross-section
  • 16mm plywood
  • 38 mm x 230 mm joists at 406 mm centres
  • 25 mm x 38 mmwood furring strips at 610mm centres
  • 12.7 mm gypsum board
38 37
3   cross-section
  • 38 mm x 230 mm joists at 406 mm centres
  • Space between joists filled with blown-in insulation materials: 3A - Cellulose blown-in attic insulation: Weathershield by Thermo-Cell Insulation Ltd.
49 44
  • 3B - Mineral blown-in attic insulation: Red Top manufactured by CCC
  • 25 mm x 38 mm wood furring strips at 610 mm centres
  • 12.7 mm gypsum board
48 45
     
4 cross-section
  • 16 mm plywood
  • 38 mm x 230 mm joists at 406 mm centres
  • 89 mm glass fibre ball insulation between floor joists
  • 25 mm x 38 mm wood furring strips: 4A - Wood furrings at 610 mm centres
44 41
  • 4B -Wood furrings at 406 mm centres
  • 12.7 mm gypsum board
37 32
5 cross-section
  • l6 mm plywood
  • 38 mm x 230 mm joists at 406 mm centres
  • 25 mm x 38 mm wood furring strips at 610 mm centres
  • 12.7 mm gypsum board
  • 63.5 mm standard metal studs (25 GA.) spaced at 610 mm centres and screwed to furring strips
  • 63.5 mm pink glass fibre insulation between studs
  • 12.7 mm gypsum board
53 45
6 cross-section
  • •l6mm plywood
  • 38 mm x 230 mm joists at 406 mm centres
  • 25 mm x 38 mm wood furring strips at 610 mm centres
  • 12.7 mm gypsum board
  • 38 mm x 75 mm wood blocking installed on flat side at 610 mm centres, and screwed to furring strips
  • 38 mm glass fibre ball insulation between the wood blocking at 610 mm centres
  • 12.7 mm resilient metal channel screwed to blocking
  • 12.7 mm gypsum board screwed to resilient furrings
46 42
7 cross-section
  • 16mm plywood
  • 38 mm x 230 mm joists at 406 mm centres
  • 89 mm glass fibre batt insulation between floor joists
  • 12.7 mm resilient metal channel screwed to joists:
   
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
  • 12.7 mm gypsum board
   
8 cross-section
  • 16mm plywood
  • 38 mm x 230 mmjoists at 406 mm centres
  • 25 mm x 38 mm wood furring strips at 610 mm centres
  • Two layers of 12.7 mm gypsum board
37 35
9 cross-section
  • 16 mm plywood
  • 38 mm x 230 mm joists at 406 mm centres
  • 89 mm glass fibre ball insulation between joists
  • Resilient furrings RC-1 by CCC, screwed to joists at 610 mm centres
  • Two layers of 12.7 mm gypsum board
50 49
10 cross-section
  • l6mm plywood
  • 38 mm x 230 mm joists at 406 mm centres
  • 89 mm glass fibre ball insulation between floor joists
  • 12.7 mm woodfibre board screwed directly to underside of joists
  • Resilient furrings RC-1 by CGC, screwed to joists at 610 mm centres
  • 12.7 mm gypsum board
45 42
11 cross-section
  • 16 mm plywood
  • 38 mm x 230 mm joists at 406 mm centres
  • sound absorptive materials in cavity between joists:
   
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
  • Resilient furrings RC-1 by CGC, screwed to joists at 610 mm centres
  • 12.7 mm gypsum board
   
12 cross-section
  • 16 mm plywood
  • 38 mm x 230 mm joists at 406 mm centres
  • 89 mm glass fibre ball insulation between floor joists
  • 38 mm x 140 mm ceiling joists supported by common 38 mm x 230 mm plate at perimeter of test opening
  • 12.7 mm gypsum board screwed to 38 mm x 140 mm ceiling joists
40 38

Project team:

Project Manager:

Jacques Rousseau

Research Report:

Research Project on the Noise Isolation Provided by Floor/Ceiling Assemblies in Wood Construction (Phase I)

Research Consultant:

MJM Acoustical Consultants Inc.

Housing Research at CMHC

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