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FAQs: Unvented attics in southern USA climates and hot climates

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FAQs on unvented attics in southern, hot USA climates

Below are some of the common questions in regards to spray foam insulation in unvented attics for homes in the hot, warm southern USA climate zones.

Doesn’t the building code require venting?
Yes and no. The building code allows builders to construct either venting or unvented attics. Specific requirements are noted for each approach.

 

Won’t the lack of ventilation cook my shingles?
Shingles degrade and fail due to direct UV radiation, not heat.  While unvented roofs do tend to raise the shingle temperature 2-3 degrees, there is no documented evidence that this significantly affects the life of the shingle.  Some shingle manufacturers will void the warranty on their shingle if it is not vented underneath and some will not.

 

Won’t moisture build up in the attic?
One of the main reasons builders usually vent attics is to allow any water vapor that enters the attic to escape before it condenses on any cold surfaces.  This is only a potential problem in the winter.  In a hot climate, there are few days where this is likely to happen.  The best way to prevent it from happening in an unvented attic is to insulate all of the exposed surfaces (roof and gable walls) to prevent having any surfaces in the attic below the dew point.  When Icynene open cell spray foam insulation is used, all the exposed surfaces in the attic have adequate insulation to prevent condensation. In addition, the air handler located in the attic will indirectly help to condition the space.

Have more questions or have a unique application question? Get in touch with our Building Science team on 1-800-758-7325.

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