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RE: lightweight concrete topping on wood

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Squeaking is usually caused by wood rubbing against each other such as
blocking or a poorly instally finish wood flooring. In most cases you do not
need blocking with wood I joists. Are they looking for sound reduction in
both directions? Is the concrete an exposed finish? You can get very good
sound isolation by using something like
http://www.kineticsnoise.com/arch/isomax/index.aspx with out using concrete,
but with concrete will be better. You probably need a consultant fore the
isomax, the drywall detailing is very important. Most finish concrete
topping on wood framing that I have seen atends to crack even with
precautions such as reinforcement, anti fracture membrane and control
joints. As a comparison, the american tile councel recomends L/720 for tile
assemblies. 1-1/8" ply helps quite a bit. iLevels software has performance
rating criteria for their products used with different assemblies.


-----Original Message-----
From: Drew Morris [mailto:dmorris(--nospam--at)bbfm.com] 
Sent: Tuesday, January 13, 2009 5:41 PM
To: seaint(--nospam--at)seaint.org
Subject: Re: lightweight concrete topping on wood

I have used 1 1/2" lightweight gypcrete used in conjunction with hydronic
heating. I believe I came across a website that had deflection
recommendations; I think I used L/480 or greater for the LL deflection. 
There may have been tile involved which drove the deflection criteria.

Andrew Kester, P.E. wrote:
>
> For a small two-story apartment building we have a wood framed second 
> floor with wood sheathing. The owner and architect are looking for 
> sound reduction, and also a stiff floor system with reduced ?squeaks?
> due to wood flexing.
>
> Right now we have suggested joists/trusses at 16? oc and ¾? sheathing 
> screwed and glued, with a 2? lightweight concrete topping. I have 
> combed thru the code and found nothing prohibiting using wood to 
> support concrete in this manner, they do mention limiting long-term 
> deflection.
>
> Is there anything in NDS about this or is this prohibited in IBC or 
> other codes? Anyone see any problems with this? We are designing for 
> the extra dead load, and have heard of this being done on other 
> projects quite successfully. Would anyone suggest anything other than 
> poly fibers for micro crack control of the lt wt concrete, maybe some 
> #3s at reentrant corners or don?t bother as it is just a sound 
> deadening topping? Should we have them spray the concrete with water 
> sealer, a bond breaker, or anything like that?
>
> Thanks,
>
> Andrew Kester, PE
>
> Orlando, FL
>


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