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I am doing some long range consulting for some friends with a home on Cape Cod.
The home has 2.5 floors plus a basement. It was constructed in the late 70's. The wall and roof insulation are typical of that period. R-11 walls and r-30 roof. Overall it is safe to say that the air infiltration rate is very high.
The basement is partially finished (about 40%) with r-11 wall insulation. The remainder of the basement has bare concrete walls. There is seal coating on the outside of the foundation but no french drain. The soil is typical cape cod sand/gravel. There are no gutters on the roofs.
The complaint is a musty humid smell coming from the basement, particularly in the summer.
They have run a dehumidifier in the past and complained that it ran non stop and increased the utility bills. Never solving the problem
I will be visiting in a about a month and have been asked to look into the problem.
I would love some input on how to narrow down the problem. If I had an unlimited budget, I know I could solve the problem with gutters,HRV's, insulation and sealant. The budget is pretty limited so the solution needs to be focused.
So far I plan to send them 2 data loggers that record temp and humidity. I was going to have one deployed in the basement and one outdoors. When I arrive I will have a months worth of Data to look at. I could also bring my Flir camera and see what it tells me.
My theory at the moment is that the house has a significant natural convective current that is drawing outside air into the home through the rim joists in the basement and releasing it through the leaky roof assembly. In the summer, the air is warm and humid. When this warm humid air hits the cold concrete walls, it condenses.
Thanks in advance,
"If you can't explain it simply, you don't understand it well enough"