Under House Insulation


Old 04-21-10, 02:53 PM
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Join Date: Apr 2010
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Under House Insulation

I have an 1800 SF home in the gulf south that is about 2 1/2 to 3 feet off the ground, set up on concrete pedestals. I had 2-3" of closed cell (hard) foam insulation sprayed between all the floor joists about 5 years ago. Even though I am in the South, I have a good shade tree cover and cooling is not an issue. However, when the temp drops down below 40 or 30 degrees in the winter, the heater has a real hard time keeping up, not to mention a significant increase in the electric bill.

I want to add insulation, but I have been told open cell foam insulation may not adhere to the closed cell foam insulation. It apparently becomes too smooth or is not porous enough. Also been told that I need to be careful not to trap moisture and have something that last.

Thanks for all suggestions
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Old 04-21-10, 04:17 PM
Join Date: Oct 2008
Location: New England
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Getting more foam to stay in place isn't a big problem. Just add some structure for it to hang on to. The cross braces that are normally used to tie one joist to another for example, could be installed and foamed right over.

Or, some wire could be stapled to the sides and across the existing foam. I haven't given it a lot of thought, but I'm sure something easy could be done. Even a piece of strapping on each side would provide a lip for the new foam to hang onto.

The other issue is the very common complaint of cold floors when they have been insulated from below. The problem is not so much the insulation as the fact that the heat above rises and it is difficult to exchange the cooler air on the floor with the warm air from above.

The other concern is that there may be other heat loss issues that will prevent any improvement in the floor insulation from changing the temperatures inside.

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