A buddy of mine, Dennis, that’s an exterminator called me the other day while I was standing in Home Depot. “Jon, I’ve got a problem and I need some of your building science expertise.” The problem he was having was being caused by some granules he had put down to repel some flying squirrels. The granules create a gas that creates a fairly strong odor. Unfortunately, this smell was making its way throughout the house. A couple issues he had already noticed were no gable vents, very few soffit vents, only one short ridge vent, and no turtleback vents. Needless to say, the attic area is poorly vented. He felt that because the attic was so poorly vented that the smell had no chance to escape and thus was coming into the house. Being the nice guy that I am, I offered to come to the house.
The house was 4,500 square feet and it was sunny and about 64 degrees. Dennis took me through the house and to the rooms upstairs that smelled the strongest (think moth balls). The worst area was a walk in closet in one of the bedrooms. The drywall seams were poorly sealed and there was a fluorescent light fixture with large hole for wires behind it (great places for air infiltration). The next place we went to was the attic. The drop down access stairs had a fairly large gap around the base, which was a bad sign for starters. Once we got into the attic, you could tell right away that it was warmer than it should have been even though it was sunny that day. Dennis was correct about the lack of ventilation as well.
I started looking around and within 10 feet of the entrance to the attic was a panned joist return. This is where the builder uses the ceiling joists, a couple of cross members, and a piece of duct board to connect a return duct to. These are NEVER air sealed and in this case, one of the cross members had a knot fall out so there was a hole in it the size of a 50 cent piece. The insulation around the area was filthy from years of being a filter for the air leakage. There were also several holes from wire accesses and none of the top plates were sealed. This is all within a few feet of the opening of the attic in a 1,500 square foot attic.
So what was making the whole house smell like moth balls? First, the gas produced by the granules is heavier than air, so it will fall through the tiniest of cracks as it spreads across the attic floor. Second, because of the lack of ventilation in the attic, the air is very still, so there is nothing to stir up the gas. Third, even though it wasn’t really hot that day, the attic was fairly warm because of the sun shining on the dark shingles. Remembering that the 2nd Law of Thermodynamics states simply that hot goes to cold, the warmer air in the attic was trying to force its way into the cooler home. Add a bunch of holes and cracks and you have a lot of access to the interior. Finally, because the ducts were not properly sealed, every time the heater kicked on that morning, the return was pulling the stinky air from the attic into the system, where it was redistributed throughout the upstairs.
Once again, building science proves that even funny smells in your home are merely a symptom of a bigger problem. I can only imagine what these people’s utility bills were considering this was a 4,500 square foot home. A simple energy audit performed by a certified professional would easily spot these issues and would give the homeowner a cost effective solution to this problem. The NRG guy strikes again.