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Re: under-slab insulation for cooler building

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Bruce,
 
        There was a thread related to this topic a few years ago.  You should be able to find it in the archives.
 
        As I see it, your situation is this: if you are always going to have the temperature at 33 degrees F. or warmer you are probably wasting money on insulation.  Once you are below the seasonal transition zone the ground temperature is probably constant.  In most areas where I have worked (in Canada) this constant would be about 34 degrees F.  In Springfield Mo. I would expect it to be only 3 or 4 degrees higher if any (your geotech should be able to advise you).  Heat flow at these temperatures should be very low unless you have moving ground water or some other phenomenon to carry the energy away.  Hence, no apparent need for insulation under the base.
 
        If this becomes a freezer you have a totally different situation and you should make this very clear to the owner.  If this becomes a freezer no matter how much insulation you place under the base you will build up a bulb of permafrost under the structure and (depending on the type of soil and the temperatures involved, of course) you stand a very good chance of totally destroying the building as a result of the foundation movement due to the frost action.  One preventative measure for this problem is to place some of your refrigeration lines below the base insulation and to dispose of (some of) your waste heat into the soil mass under the base.
 
Regards,
 
H. Daryl Richardson
----- Original Message -----
Sent: Friday, August 05, 2005 1:26 PM
Subject: under-slab insulation for cooler building

We are designing a cooler building which will be located in central Florida.  In an effort to reduce cost, the contractor wants to eliminate the under-slab insulation.  The building is approximately 170? square x 80? tall with (4) 2-million gallon tanks inside and the interior temperature is to be a constant 33 degrees Fahrenheit.  The foundation is a 2?-0? thick mat? basically a 2?-0? thick slab-on-grade and will have a vapor barrier under it.  Even though the owner can?t allow the contents to freeze (he?d lose a lot of money), we are concerned about a malfunction causing the interior temperature to drop below freezing (probably not extremely likely) or temperature variations allowing the temperature to be below freezing in certain spots.  Not to mention the problems that could arise if the building is someday converted to a freezer building.

 

Are we just worrying too much?  Should we go along with eliminating the under-slab insulation?

 

 

Bruce D. Holcomb, PE, SE

Structural Engineer & Vice President

Butler, Rosenbury & Partners

319 North Main, Suite 200

Springfield, MO 65806

417-865-6100

417-865-6102