Re: Sound Class Transmission Rating
From: Jim Mayer (
Date: Sun, 8 Mar 2015 07:11:17 -0700 (PDT)

I live in an apartment, not cohousing, but it was new construction and we
asked similar questions before moving in. We have an end-unit townhouse on
the top three floors of a four story building.

Our walls have an STC of 52 and our floors have an STC of 62. I didn't know
about IIC so I didn't ask. I will the next time I move.

Our experience is that we don't hear much in the way of conversation or
music from our neighbors. If someone shouts we'll hear it, but normal
conversation is inaudible. We don't hear vacuum cleaners or garbage

What we do hear is "thumping", especially when people run up and down the
stairs in the townhouse next door. There is an apartment below us and our
downstairs neighbors definitely hear impact sound.

At one point our downstairs neighbors performed an experiment with us. My
wife went downstairs and I walked around on our lower floor and stairs.
When I walked barefoot and took my weight on my forefoot there was no
problem (feet are amazingly good shock absorbers). When I landed my steps
heel first (a "heel strike") the sound came right through. Carpet on the
stairs made little difference. Rugs on the floor didn't help either.

I walk quietly, which is fine for me, but is not a viable solution... A lot
of people (apparently including all kids)  land their steps heel first and
the sound of the impact travels right through.

My recommendation: pay for the good construction.

On Mar 7, 2015 9:14 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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