Attic Ventilation - January 2020 FRM

Tue, Jan 14, 2020

Attic Ventilation

Mike Fulton, National Manager Technical Training and Compliance, O’Hagin LLC

Attic ventilation has been a standard in building construction and living envelope air quality for years. Although the language in the code has changed slight­ly over the years, the intent is still the same: to furnish adequate cross-ventilation to all rafter or truss spaces with ventilators located at or near the ridge and at the eave or cornice, creating a balanced intake and ex­haust system.

As building designs changed from gable end to hip roof designs, balance has many times been ignored, causing excessive heat build-up in the upper portion of the attic space. The results are two-fold. First, great­er heat can significantly decrease the life of the roof coverings and underlayments. Second, higher attic temperatures mean greater heat transfer to the air conditioning ducts. Lowering attic temperatures de­creases the radiant heat transfer not only to the living envelope, but to the AC ducts. The ducts, which may have only an R-3 to R-8 rating, are a pathway to in­creased air temperatures (by a few degrees) from the air handler to the last drop, thus reducing the efficien­cy of the AC system and providing that initial “blast of hot air” that gradually cools when the AC system kicks in. Air handlers installed in the attic have an even greater heat gain, adding to the increase in heat. In some cases, by decreasing attic temperatures through improved ventilation, homeowners have experienced between 10 to 20 percent decreases in utility costs. Read more

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