Re: Sound Class Transmission Rating
From: R Philip Dowds (
Date: Sat, 7 Mar 2015 07:57:44 -0800 (PST)
Severe budgeting problems forced compromising on Cornerstone construction 
standards, so our walls and floor/ceilings are of the most basic assemblies:
PARTITIONS between units are 5/8” firecode gypsum board each side of 2x4 or 2x6 
studs, insulated.  We are not happy.  US Gypsum manuals put this kind of 
construction at STC 46.
FLOOR/CEILING ASSEMBLIES between units are typically hardwood over structural 
plywood; 2x10 floor joists; and 5/8” firewood gypsum board on strapping.  We 
are not happy.  The manuals say STC 39 and IIC 56.
To try to stay happier, we have learned be quiet in our units.  A couple of 
years ago, I retrofitted one of our common room ceilings with an additional 
layer of 5/8” on resilient channels, and the upstairs occupant is much happier.


> On Mar 6, 2015, at 10:19 AM, LESLIE PETERSON <leslie.peterson [at]> 
> wrote:
> Can anyone in existing multi-family cohousing tell me:
> 1.  What sound class rating/s do you have in your living units for a) 
> floors-ceilings and b) walls:
>     -  Sound Transmission Class (STC, airborne sound), and
>     -  Impact Insulation Class (IIC, impact sound)?
> 2.  How is this working for you and your fellow cohousers?
> I am looking for a NUMBER - and how satisfied you and/or your fellow 
> cohousers are.  The STC (and possibly IIC) rating number should be in the 
> architectural plan and in contract/s with the subcontractor/s who built the 
> floors-ceilings and walls.
> I am NOT looking for info or suggestions on materials and design (e.g. 
> carpets vs no carpets, number of sheetrock layers, hollow wall designs, wood 
> vs cement construction, etc).
> I have read Cohousing-L threads on the topic from March, 2008 and February, 
> 2012 regarding acoustics which include indications of some unsatisfactory 
> experiences and some varying industry recommendations.  However I do not see 
> specific info on what ratings have been built in multi-family cohousing units 
> and how cohousers experience their sound insulation.
> I am looking for specific info on:
> 1) STC/IIC rating/s (a rating is a number) that have been implemented for a) 
> floors-celings and/or b) walls, and
> 2) How satisfied people are with their acoustics (note that satisfaction 
> level is meaningful when related to a rating number only).
> Many thanks in advance to those willing to check their records!
> Leslie
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