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Insulating under a raised slab house


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03-10-01, 02:18 PM   #1  
We raised our slab home to avoid flooding problems in our area but now have frigid floors. The house was raised 11 feet off the ground and the underside of the original slab is exposed to the elements. How would you suggest insulating the underside of the concrete slab which is being supported by cinder block piers? This is a large area.

 
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03-11-01, 03:39 AM   #2  
You must have quite a flooding problem to elevate the house 11 ft. Before you insulate look into the cost of adding radiant heating to the slab. Normally this is imbedded into the slab as its being poured, but call in a Representative & have him look at adherring it to the bottom of the slab.
As far as insulation, afix extruded polystyrene sheets to the slab and on the sides. These have an R value of 3.5 per inch. Determine your insulation requirements from the local building department. Use a mesh material and parge over the mesh. Any gasket or thermal break between piers & floor?

 
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03-11-01, 10:17 AM   #3  
Raised house

Thanks Allan, There are no gaskets or thermal barriers between the piers and slab. Being in the South we do not see much radiant heat but it is sure worth checking out. Even at 50 degrees outside its really cold in the house with full heat. I am thinking about building a ceiling to support the insulation material. Should I leave air space between the slab and the insulation? Any suggestions on R value for a climate that rarely gets below 25 degrees? What do you think about a spray foam product? I am afraid of loosing it over time and it is expensive.

 
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03-11-01, 07:26 PM   #4  
A sprayed on foam insulation would be a good option. If you go with the rigid insulation, do not leave an air space between it & the slab. Insulation works by restricting air movement. Building a ceiling for the insulation would be costly. The spray applied and a glued rigid will stay on its own. The parging was mostly for looks, although it will also keep the vermin from burrowing into the insulation. Insulation requirements vary from zone to zone, but here in South Eastern Ontario, R 28 is used on the under side of a floor if it is below a living area. The temps here get a great deal colder than 25*.

 
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