Quote:
Originally Posted by hayden55
How exactly do you know if you have adequate attic ventilation? I'm used to thinking about homes where the air changes per hour and humidity ranges have standards. Besides not seeing rusty nails or sweat on surfaces or mold it seems odd to talk about. Although, if you guys could see the houses they build in the south it pretty much shows they have no standards or inspections on attic ventilation.
This brings to mind one of the standards of one of the energy efficiency groups where they build house to have 1 air change per hour at 50 pascals of pressure. Which means the home is super efficient, it just needs humidity control, a hepa filter, and an air exchange system installed.
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For air-conditioned homes, if the temperature in the attic, directly above the ceiling insulation, is no more than 10-degrees above the ambient outdoor temperature, then you have 'adequate' ventilation for both summer and winter.
100-degree dry-bulb temperature outside:
157-degrees outside on top of asphalt shingles in full sun.
146-degrees under the roof decking.
110-degrees just above the insulation, you're 'DONE.'
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If you have un-vented gas heating in the home, you'll be loading the interior air with water vapor. It will do all it can to permeate floors, walls, and ceiling.
Any surface below dew-point that it can reach will produce condensation, bacterial activity, rot, and attract termites. It's why 'TYVEK' or related breathable barriers are mandatory in all new construction.
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If a contractor has installed blown-in insulation, make sure they haven't smothered all the soffit inlets. You've got to have convection-driven air circulation up there.