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Unvented Attic Space

To vent or not to vent, that is the question! Home inspectors, building scientists and others seem to debate this point. We are seeing more “sealed” attic spaces in many new builds. These homes have no attic ventilation. Soffits are closed and no roof vents are present. Proponents of this construction claim that ventilation is not needed because because there is no air movement or air loss. Closed attic conditions require 3 methods. A class 1 vapor retarder should not be installed on the attic floor or at the ceiling above the attic space. Because closed cell foam insulation has a vapor barrier, additional vapor barriers will cause moisture to be trapped. Air impermeable insulation board installed between rafters or trusses should be sealed to form a continuous layer. The joints should be sealed to form a proper uninterrupted vapor barrier.  In colder climates, air impermeable insulation should be a class II vapor barrier, or should have a class III vapor barrier applied to the attic ceiling side of the insulation. What other conditions should a home inspector be looking for and how should your client be advised;

  • Foam insulation under the roof deck may void asphalt shingle manufacturers warranties
  • Leaks may not be visible until the deck has deteriorated significantly and shingles begin to fall off
  • If the deck is deteriorated and has to be replaced, the insulation will also have to be replaced, increasing the cost
  • If the house is completely spray foamed, recommending a properly sized Heat Recovery Ventilator (HRV) is installed

If the house has not been built, I recommend that spray foam is used on the attic floor. Proper attic ventilation can then be installed using soffit and ridge or roof vents. I have advised many clients with this advice and feel that it is the best way to provide adequate ventilation and still ensure the house is properly insulated.

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