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Should I or can I safely insulate interior ceilings?

I own a poorly insulated home and would like to insulate the ceilings with 2" of Dow foam? I live in Zone 5A. The ceilings and walls are lath and plaster. My attic space is also not insulated. My plan is to also insulate the exterior walls with Dow foam and install new siding. The exterior walls have painted siding but NO sheathing.

Mike

Asked by Michael Craig
Posted Mon, 12/09/2013 - 10:44
Edited Mon, 12/09/2013 - 12:55

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Michael,
Once you have removed your existing siding, you probably want to install a layer of sheathing. The sheathing will provide bracing for your walls (making them better able to withstand winds and earthquakes) and will also improve your home's airtightness (especially if you tape the seams of your OSB or plywood).

After your sheathing is installed, you can install a layer of rigid foam on the exterior side of your sheathing. Here is more information: How to Install Rigid Foam Sheathing.

If you want to insulate your ceiling, the easiest way to do so is to install cellulose insulation on your attic floor. If for some reason you can't do that, you can install 2 inches of rigid foam on your ceiling, as long as you realize (a) that 2 inches of foam gives you only R-10, which isn't much R-value, (b) you need to pay attention to air barrier continuity at the intersection of the top of your walls with your ceiling, and (c) the foam has to be protected on the interior with a new layer of gypsum wallboard.

Answered by Martin Holladay, GBA Advisor
Posted Mon, 12/09/2013 - 12:48

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