Bungled Basement Soundproofing

Recently, a client retained me to review his basement soundproofing job. The job was done by his contractor who was not a specialized soundproofing contractor. As a result, it was bungled.


State of the soundproofing job

At my site visit I have found a finished basement, recently renovated, as seen on this photo.

Finished basement soundproofing

The client provided a picture of the job in progress. Ceiling joists are 2” x 10” wood. There are green Sonopan panels [reference 1] attached to joists. 5/8” drywall is attached over the panels.  There is 3” rockwool insulation between joists. Floor above the basement is finished with hardwood.

The client’s contractor, not being a soundproofing contractor, though that this was an adequately soundproofed assembly. The client was not satisfied. My inspection and test proved that the client’s dissatisfaction was justified.

This type of assembly (not including the duct chases) has STC value 35 as approximately simulated using INSUL program [2].  This is completely inadequate.  Ontario Building Code requires minimum STC 50 between residential units.

Ceiling done by a soundproofing contractor

Ducts in the ceiling are enclosed in a drywall chase, as visible in the client supplied photo. There is no insulation around the ducts.

The assembly with Sonopan panels installed by the client’s contractor is not included in the list of acoustically tested assemblies [3] by Sonopan manufacturer.  However, their website is misleading. It appears to imply that this assembly is acceptable.

Heating and air-conditioning in the house are by forced air furnace located in the basement. Ducting for the basement is a separate zone, with dedicated ducts.  As a result, there is no issue with noise conducted by ducts, as is the case in most basement apartments.

Noise reduction test

I have performed a quick and simple noise reduction test.  The test result was close to the noise reduction value obtained by approximate simulation of the ceiling assembly. The simulation also indicated that the sound transmission class of the existing ceiling is STC 35, which is low.

Basement soundproofing improvements

The client wished to improve the basement soundproofing without lowering the existing ceiling surface. The entire newly completed ceiling needed to be modified. 

I have recommended to rip out the existing drywall and Sonopan panels. Add insulation to thickness of at least 6 inches. Then install resilient channels 24” apart and 5/8” noise reducing drywall. This type of ceiling assembly has STC better than 50 [4]. Reduction of impact noise by this assembly is noticeable, but less so than reduction of airborne noise.

Surface of this ceiling will be ¼” higher than the existing drywall surface.

Soundproof ceiling

Alternatively, instead of noise reducing drywall, install two layers of 5/8” Type X drywall with Green Glue [6] between layers.  If you are installing two layers of drywall, install the resilient channels 16” apart. This assembly has STC about 57, based on INSUL simulation.

Surface of this ceiling will be 3/8” lower than the existing drywall surface.

My detailed recommendations include instructions that can be executed by any competent contractor, or preferably by a specialized soundproofing contractor.

Should you hire a soundproofing contractor?

The moral of this story is that a bungled soundproofing job is twice as expensive as a competently done job.  The basement soundproofing needs to done twice, if it is not done first time by a soundproofing contractor. Better still, get proper soundproofing advice from a soundproofing consultant in advance.  He will then refer a specialized contractor.

If you wish to contact the author of this article to request a similar consultation, preferably before you allow your contractor to botch the job, click on the button below.

[1] Sonopan
[2] INSUL simulation program
[3] Sonopan assemblies
[4] National Building Code of Canada 2015, Division B, Table, Assembly No. F8d
[5] Green Glue 

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About the Author Ivan Koval

The author is the publisher of the Soundproofing.Expert website. He is a soundproofing and building acoustics consultant working in Toronto and GTA, Ontario, Canada. Telephone (416) 471-2130

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