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My garage has a ceiling with fiberglass insulation over plastic air spacers leading to vents under the roof shingles. There is no plywood or drywall over the insulation. The walls are insulated and finished. The soffit vents are pulling in the smell for about 3 weeks every spring. I wondered if i could just seal off the soffit openings. Maybe the vent spacers are too small to vent the air from the soffits, and the rest gets pulled back into the garage. I didn't want to go to the trouble of putting up ceiling plywood.The center part of the garage has no ceiling aboveit and is open to the attic part of the garage.

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Without knowing roof profiles, it would be difficult to comment, but in general, increasing the vent's elevation higher above roof should decrease its ability to backdraft. Similarly, some amount of positive pressure from a clean inlet (low on the wall) would also prevent backdraft. Is it possible the house is negatively pressurizing the garage. A makeup air handler would help in this case. – HerrBag Feb 8 '14 at 21:35
I should have added that the house is 50 feet away from the garage.The smell is getting pulled into the garage soffit vents. smell ooriginates from adjacent house. – darren Feb 8 '14 at 22:22
A picture showing your garage and the adjacent house's offending vent pipe may be helpful. It's kind of hard to imagine how the smell is making it to your garage soffits. – getterdun Feb 9 '14 at 4:23
You need to isolate the attic portion from the occupied portion, even if it's just plastic sheeting. – bcworkz Feb 9 '14 at 18:52

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