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Have You Sealed Your Crawlspace?

1638 Views 11 Replies 8 Participants Last post by  LLigetfa
Our summer place has a crawlspace. Years ago the pipes and beams had a lot of condensation. We laid plastic sheets on the dirt and added ventilation which stopped the condensation but the first floor of the house is still damp most of the time. The thin plastic is beginning to decompose and some of it has been moved around over the years. I believe that most of the dampness is coming up from the crawlspace. From what I've read, the new theory is not to ventilate but to seal it off completely. They do this by laying a 20 mil vinyl fabric on the dirt, sealing the pieces together. They also run it up the block walls and seal it at the top and around the footings. Then they close off all the vents and place removable covers on the access points. Sealing drains and dehumidifiers are also available if necessary. The job is fairly costly. I could get the materials and do it myself but I hate going down there anymore because some areas have only 1 foot of clearance. :eek: Has anyone sealed their crawlspace with "Clean Space"? :)
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Code here says that if a crawlspace is not conditioned space, it has to be vented to the outside. I argued with the building inspector that venting in the Summer causes hot moist air to condense in the coolness of the crawlspace creating conditions for mold and mildew.

My former home had a crawlspace that was not vented to the outside. It had poly over an earthen floor that wrapped up onto the walls. The poly was not sealed where the wall met the earth so I had a lot of humidity problems in Winter. The contractor that built the house put 2000 watts of electric baseboard heat in the crawlspace but then put the thermostat up inside a closet. Since the thermostat didn't sense the temperature in the crawlspace it was either too cold or too hot. I kept turning it down but the wife always turned it up because the floors got too cold. Too much heat in the crawlspace caused moisture to be evaporated from the soil which migrated up the poly and condensed on the cold side of the batt insulation and air infiltration over-humidified the entire house. I don't know how it passed inspection because it wasn't to code. Code says the thermostat has to be in the living space but did not specify that it has to be remote sensing. I argued it with the inspector and he let me move it down to the crawlspace.

I put in a claim to the new home warranty people and raised a big stink with the building inspector. I had pull down all the poly and the batt insulation to dry everything out. It was then I found out the builder used 3 - 1/2 inch batts in a 2x6 stud wall leaving a 2 inch air space on the cold side. I got the builder to supply 2 inch rigid foam insulation that I cut to fit between the studs on the cold side and put back the batts after everything dried out. I sealed the bottoms of the stud cavities with 2 inch foam and sealed the poly to it.

If a crawlspace is not vented to the exterior it is considered conditioned space and as such has to be fire rated. When I built my current home, I drywalled the crawlspace and a painted concrete floor over crushed stone for drainage. In the Summer, I don't move any air through it as hot moist air would only condense in the coolness. In the Winter I draw air up from the crawlspace with a 650 cfm blower that moves it across my wood burning fireplace. The makeup air is drawn down at the opposite end of the house so it evens out the heat and warms the floors.
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