Balanced Ventilation in Attic
Austin G| Posted inGeneral Questionson
I’m working on an early 1900’s house that had essentially zero attic ventilation. There is a gable opening on one side and the eaves are non-existent – so no way to ventilate there. The roof is also nearly new metal.
I know the prevailing wisdom is against attic fans. It seems like the argument against them is that they create negative pressure in the attic space, pulling conditioned air out of the home, negating any benefit. Would balanced ventilation with two fans negate this problem?
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Yes, balanced ventilation would work, but at an energy penalty due to the cost of running the fans. Passive ventilation is almost always a better solution. If you tell us where you are located, we can provide more recommendations. Mild and/or dry climates need less ventilation than cold and damp climates. Also, if you aggressively air seal and insulate the attic floor, you need less attic ventilation. Gable and ridge vents might be enough.
I’m just outside Kansas City Kansas. The attic floor is very well air sealed (now). The only ventilation this house has is a single gable vent. Whoever did the roof didn’t cut a ridge vent.
Thank you
Why is the existing attic ventilation deemed inadequate? (What are you trying to achieve here?) If there aren't any obvious moisture issues with the structural wood in the attic the gable vent is probably already doing enough.
With a ridge vent there needs to be soffit vents of equal (or better yet, larger) cross sectional area, otherwise a ridge vent depressurizes the attic causing it to pull air from the conditioned space below. In order for a soffit-to-ridge approach to be effective requires closing up your gable vent, which would otherwise be a short-circuit, reducing the flow at the soffits.
There are some areas of rot. I’m in the process of addressing the obvious issues (crawlspace, etc), but just worried it’s not going to be enough.