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Insulating walls & ceiling for a detached swim spa room

I live in zone 6 climate and want a building to house a swim spa for year around use. If I have an interior vapor barrier, 2 x 6 walls with fiberglass insulation, OSB and house wrap on the exterior. Can I add 1-1/2" rigid insulation to the exterior before I side it with cement fiber board? How about the ceiling with vapor barrier and no penetrations (for lights etc.) can I use standard blown insulation if the attic is well vented? I plan on purchasing a dehumidifier designed for pool room use.
Please advise!

Asked by Mark Cranston
Posted Tue, 01/07/2014 - 22:48


1 Answer

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The type of building that you are describing (a "swim spa room") is associated with a very large number of roof and wall failures. The constant humidity in these rooms very often leads to catastrophic wall rot and roof rot.

Your proposed assembly -- an interior vapor barrier, 2 x 6 walls with fiberglass insulation, OSB and housewrap on the exterior -- is doomed to failure.

There is only one possible approach to this type of building, and that is the PERSIST approach. You need to install a layer of peel-and-stick membrane on the exterior side of your wall and roof sheathing, followed by several layers of rigid foam, installed with staggered seams.

For more information on the PERSIST approach, see Getting Insulation Out of Your Walls and Ceilings.

Answered by Martin Holladay, GBA Advisor
Posted Wed, 01/08/2014 - 08:39

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