07:24PM | 06/27/07
Member Since: 06/26/07
2 lifetime posts
Hi guys,

I am looking for help with a condensation problem in the crawlspace under my house.

It is approx. 25' x 30' in size and it slopes from about 1' to 4' high. The dirt floor is covered with plastic. There are 2 vents on the front of the house -below grade going into the crawlspace, they have been dug out around them. They are 6" x 10" screened and louvered so they can be opened and closed. The 2 vents on the backside of the house are same but above grade - I'm on a slope. There is also a cement block support wall that divides the crawlspace in half. It has an access opening at one end to get through to the other side 24" x 30" and has 2 cement blocks left off the top at the other end for cross-ventilation.

In the humid summer, the fiberglass insulation between the floor joists drips large amounts of condensation down onto the plastic covering the dirt floor. I am worried about mould forming on the joists or dry-rot.

Last summer, I took one above-grade vent out and installed an exhaust duct through it with one of those inline furnace duct booster fans (160cfm). With the duct sucking from ground level, it didn't help.

This year, I added another fan (200cfm) to the other above grade vent. It didn't help either.

There is a 24"x30" outside entrance door on the above grade side of the crawlspace. Would it help if I installed a screen on this door or should I try something else?

Any help would be greatly appreciated. Thanks.


07:00AM | 06/28/07
Member Since: 04/25/05
1916 lifetime posts
"In the humid summer"

That is the problem, humid air. You WANT TO KEEP IT OUT, NOT BRING IT IN.

You did not give you location, but during the summer much of the US, east of the Rockies, will have a high dewpoint. Might be 70 or higher.

A crawlspace is going to be cool to start with as it is with close contact with the ground.

Then you often have cold ducts that the air can get to, even if insulated.

And that increases the relatively humidity level in the crawlspace. Enough for mold and mildew and often enough for condenations.


Do a google on Conditioned Crawlspace and on Sealed Crawlspace.


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