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no ventting in attic

I just watch ask this old house s10 eo13 were tom help a home owner stop ice dam by spraying foam insulation .I was surprise that there was no venting of the roof. I would think this would make the roof very hot in the summer and decrease the life of the roof shingles .

Len Manchester N.H.

Re: no ventting in attic

Attic venting is more for the winter than the summer. The purpose is two-fold: prevent moisture buildup (which results in condensation on the underside of the roof, which results in rot and mold) and to prevent a warm roof in the winter. A warm roof melts snow and ice, which refreezes when it contacts the cold, uninsulated overhang causing an ice dam.

The spray-foam insulation resolves the first issue by completely blocking moisture from the underside of the roof. (Closed-cell foam is necessary to provide a vapor barrier; open-cell foam is unsufficient.) The interior surface of the insulation remains warm, preventing condensation.

It resolves the second issue by preventing heat loss through the roof, so the outer surface of the roof doesn't warm to the point of melting ice & snow.

As for summertime temperatures, the cooling effect of ventilation is very minor. It's possible the life of the roofing material may be shortened without ventilation, but the money spent in more frequent roof replacement is far less than repairing mold or water damage.

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