Insulating Attic Floors Recommended?


Old 03-19-14, 08:56 AM
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Join Date: May 2010
Location: Canada
Posts: 11
Insulating Attic Floors Recommended?


Renovating the Attic. It has no heat source but I just got spray foam insulation and it is surprising very warm in the Winter. Not sure about the summer yet.

Anyway, working on replacing the floor now. I have bags and bags of rigid insulation pieces from previous jobs and I was wondering if it will do anything if I put the rigid pieces under the floor between the joists? Could it help with muffling sound between levels or prevent some heat from travelling up in the summer? Will it do nothing? Is it generally recommended or not recommended to do something like this?

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Old 03-19-14, 09:06 AM
Join Date: Oct 2008
Location: New England
Posts: 9,990
Hi steve,
One of the kinks in adding insulation is the problem of moisture management. That nice warm winter attic is now home to lots of warm moist air from below. As long as the surface of the foam or hopefully the fire rated covering, remains above the dew point you are all set. But too much insulation in the floor and suddenly you start to grow mold.

The correct approach is to add all of the insulation value to the roof and gable ends and remove the floor insulation. In addition, some portion of the heat below is then directed to the attic along with a return. If the foam application covered the rafters as well as the space between you are all set. If the rafters are exposed, then they will be the coldest surface.

Check local codes on the fire rated covering. If this will be living space be sure you have proper egress.


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