hip roof ventilation options
What is the knock against powered ventilators if there is adequate provision for intake air? We’re buying a single story house that has ~1800 sq ft of attic above the living space, and another ~1300 sq ft above the garage. The peak over the garage isn’t as high as the peak over the house. It’s a hip roof, so there isn’t nearly enough ridge for ridge vents. They installed powered ventilators when the house was built 20 years ago, one above the house, one above the garage, and they seem to have done their job. It’s time for a new roof, so we’re considering options. Ridge vents are out, box vents are ugly, so turbines or powered ventilators seem to be all that is left. As long as everything is sized to keep the attic pressure neutral, relative to the living space, are powered ventilators really a problem? Any other suggestions?
Thanks,
Terry
GBA Detail Library
A collection of one thousand construction details organized by climate and house part
Replies
Power vents tend to depressurize the attic and tend to pull conditioned air from the house.
I seem to recall one study the showed operating the power vent fan increased the AC load.
Walta
tarique,
Ideally an attic is slightly pressurized so that it doesn't draw air through the ceiling from the home below, which due to the stack effect will already have a tendency to move in that direction.
No matter how large the intakes, with mechanical exhaust is is extremely unlikely you will have neutral (never mind positive) pressure in the attic.
So that's where the advice to avoid powered attic ventilation comes from. Whether those conditions will cause problems in your attic, especially as they haven't so far, is an open question.