Attic Ventilation
Question:
I need to put a new roof on my single-family dwelling. The house originally had gable and soffit/eave vents. The roofing contractor suggested that we install a ridge vent when new roof is installed. Should the existing gable vents be blocked off or does it not matter? I have read some debates about whether or not the combination of gable and ridge vents substantially reduces the effect of the soffit vents by having the intake now at the gable vents and exhaust at the ridge. Would this type of ventilation affect the truss warranty?
Answer:
Any truss warranty that you may have will be with a specific manufacturer, so we really cannot comment on the terms of the warranty.
This is really a question of whether or not the new ventilation configuration will allow moisture build-up in the attic. The design assumption for all wood framing in structures is that the moisture content will be below 19%. Most structures reach average moisture contents of 8-11% after construction. As long as the ventilation does not allow moisture build-up in the attic, the trusses should be fine. We contacted an engineer at the National Association of Home Builders (NAHB), who told us: “You can't have too much attic ventilation. I suspect that the combination of the gable ventilation and soffit ventilation is enough without the addition of the ridge ventilation, but the addition of the ridge ventilation shouldn't hurt the ventilation. I would leave the existing ventilation open.”