Thanks for an intelligent and informative article about unvented attics and the use of closed-cell spray foam ("Insulating Unvented Attics With Spray Foam," 3/07). After mentioning the common misconception that code-required venting significantly lowers the surface temperature of asphalt shingles, the article goes on to state that a properly constructed unvented roof assembly "is immune to the moisture problems that occur in vented assemblies and is much more likely to be energy-efficient."

The article also points out that several major shingle manufacturers now guarantee shingles installed over properly constructed unvented roofs.

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