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Old 09-03-2007, 10:42 AM   #1
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musty crawlspace

We live in southern Maine in a passive solar home built in 1978. There is a partial basement containing the furnace, hot water heater, and radon water mitigation unit. The radon unit "sweats" and it is often damp on the concrete floor around it. There is a crawlspace with a dirt floor under the rest of the house. Electrical wires, heating ducts, and water pipes all run from the partial basement under the crawlspace.

The fiberglass insulation in the crawlspace is failing and we have some issues with mildew/mold under there where the damp has latched onto the ceiling of the crawlspace/bottom of the floor of the house. There are four of us living in the house and my son does seem to be sensitive to the mildew - he has a constantly runny nose. He has tested negative for allergies to a host of things in our environment (3 times). So, we are looking to dry out and clean up the crawlspace as a last resort before moving.

The current recommendation is to rip out the insulation, sanitize the ceiling/floor of the crawlspace, put sealed 6 ml poly down and blow insulation around the perimiter of the house.

We're a little concerned that this solution will turn the ground under the poly into a moldy, muddy, mess that will kick out spores around the entire house. And the pipes might freeze if only the perimiter of the house is insulated.

Anyone have any ideas about how to insulate a crawlspace enough to keep the pipes from freezing while keeping some airflow to keep the dirt dry?
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Old 09-03-2007, 11:58 AM   #2
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There should be vents in this crawl space to the exterior. You could attach a fan to one of the vents with a humidity sensor. When it gets to a certain humidity level, it turns on automatically. You can buy weather stations with remote sensors to monitor the level from anywhere in the house. Cover the dirt with the plastic and/or cover it with 2" of concrete over rigid foam insulation, buy a dehumidifier and run it in the space.
Pull out all the wet insulation and treat the mold as you said. Then put new insulation back in. Take rigid foam insulation and line the exterior walls. If you have pipes running through the space, make sure they're insulated.
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Old 09-03-2007, 03:53 PM   #3
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You should do the clean up and sanitizing in your case, but we found that simply just greatly increasing crawlspace ventilation was the key in our situation.
We live in a 1977 A-frame that we built in coastal NC where there is very high air and ground humidity. We had a problem for a number of years with excessive crawlspace moisture, white mold on the wood joists and subflooring, dripping pipes and ducts, etc.
In our case, a plastic ground cover would have only contributed to the excess moisture problem by trapping moisture over and under it.
We finally solved the excess moisture problem by installing a 10" louvered exhaust fan (actually designed for dairy barns) built into a pressure-treated wood crawlspace door. It runs 24/7 with all vents open except for hard freezing weather, when we close the vents and unplug it for the winter. The humidity is way low here that time of year anyway.
We contacted tech support of W.W. Grainger, and they recommended an exhaust fan based on the cubic footage of our crawlspace (length X width X height), and I went with one twice that CFM size. It still only has a 1/30 hp motor, and hardly uses any electricity.
I built the p-t wood crawlspace door to accomodate the fan out of 5/8" p-t plywood with a 14" square hole cut in it. I put a layer of p-t 2X4s around the hole on the outside and two layers of p-t 2X4s on the inside to make room for the fan and louvers. I added a layer of small mesh hardware cloth backing to regular screen wire to keep everything out in the outside outer part. The entire fan assembly just slides in and bolts onto the frame on the four corners of the inside 2X4s.
It's very low maintenance. I just oil the little motor about 3-4 times per year with regular machine oil.
Keeps it all comparatively bone dry, even in this high humdity. No mold, no dripping, etc.
Good Luck!
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