Housing and Community Development

This message has been cross posted to the following Discussion Forums: Custom Residential Architects Network and Housing Knowledge Community .
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A small holiday contribution to our shared knowledge.
May the Holidays mostly visit Joy upon You and Yours.

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Mike Mense FAIA
Owner
mmenseArchitects
Anchorage AK
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Great illustrative presentation on condensation.

One possible solution may be an unvented attic. In new construction is it simple to spray foam insulation on the underside of the roof deck. For existing conditions such as your example, it is similar to what you stated - place rigid insulation on top of the roof. The existing attic insulation should be removed and all roof/soffit penetrations sealed. In southern climates an unvented attic is 85 degrees on a 100 degree summer day. In essence, the plane where the temperate difference takes place is moved to the exterior envelope. Minimizing the opportunity for condensation in an interstitial space.

Happy Holidays (hopefully, free of brown water)

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James Lawrence AIA
Project Leader
Quorum Architects, Inc.
Fort Worth TX
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