Posted: 12/7/2008 3:06:17 PM EDT
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I own an older home which was built around the 1950's and under the house there is no plastic on the bare ground. I'm trying to insulate this house the best I can to save on heating and cooling costs. I would also like to insulate the floor from under the house also if the savings are worth it. Do both of these sound like good ideas? I'm only considering the plastic sheeting on the ground below the house to help prevent moisture from coming out of the ground and getting between the insulation and floor during the summer months. Any suggestions or comments will be greatly appreciated. |
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You could pour a thin slab in there so the ground is not exposed. Another thing you may look into is humidistat and thermostatically controlled crawl space vents. I put them in a crawl space similar to yours and they keep it pretty dry above ground. I did insulate the floor and there was a major difference the first night that was totally noticeable. I put a thin fan-fold rigid foam over the bottom of the joists to keep the soft insulation from hanging down past the hangers after installation. I did leave a space around the pipes so they were not covered but the house has a heater in the crawl space to keep it above freezing temps in the cold winters ( northeast PA ).
The only thing I did not do was pour a slab. The water table is high in the area and the floor is sand. My fear is that if I did away with the sand and made the floor solid, there would be nowhere for the water to go. Currently the sand floor lets the water flood slightly ( a couple of inches at best ) then recede back ( there is a sump pump that expedites this too ). |
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Quoted:
I'll ditch the floor insulation but why do I need the pea gravel? Couldn't I just do it in true Alabama style and just hold down the plastic with old tires and car parts?  You probably don't need to ditch the insulation. I did because I have to keep the temp up in the crawl space so the plumbing doesn't freeze. I don't know why pea gravel but that's what they put in up here. Plastic on the ground then pea gravel. I would'nt put in a slab because it's a pour vapor barrier. Like a three mill or thicker plastic will do a good job. |
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Is it wet down there now or dry?
I would recommend 6 mil plastic. It's far more durable than the 3 mil type. Not a lot more expensive either. More and more people are recommending that crawlspaces be sealed up. I'm planning to seal mine. Check out this site: Crawlspace Guide Or this one: Crawlspaces |
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Just put the 6 mil black plastic down, you don't need anything on top of it, nothing's down there to move it like wind or whatever - it's not going anywhere. Fuck putting down pea gravel or concrete, why turn a simple and cheap job into an expensive and hard job? For what?
Insulate your floors, it will make it much more comfortable. I have the 3 1/2" fiberglas batts held in with 18" or so wire insulation holder doo-hickeys. Insulate your pipes, both hot and cold with the grey foam stuff you get in 3' lengths at any of the Lowe's/HD types. I live in North Alabama and we haven't had our pipes freeze in 14 years and 10 of those were with an unvented gas logs, hence there really isn't any hot air flowing through the heating system warming up the crawl space. Unless you live on a mountain in Jackson County, you're not any colder than me. Good luck. Merlin |
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Here if you seal the edges of the plastic to the foundation it's part of radon control. I dunno if you guys have radon issues down there or not.
People around here don't use gravel though. Seems to me the pea gravel would be awful and hurt like the devil when you go under there to work on stuff. OW 
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Go to your local builder supply, ilbt Lowes, Home Depot or other and get some Visqueen vapor barrier clear film 6 mil or better.
You do not need pea gravel or a slab installed in a crawl space. 
When you cover the soil in your crawl space, I suggest you leave a 2 to 4 inch pull back of the plastic film from the foundation perimeter and any support columns. This was suggested by my termite contractor. I did what they suggested and there is less condensation than before I ran the visqueen up to the foundation. In the first year after I installed the visqueen, I noticed more creaks in the floorboards throughout the house due to lower humidity in the house. One or two doorways are tighter and another sticks per the season. Overall, I think the house is more comfortable with the lower humidity. The insulation to the attic is a whole other story, that made our house much more comfortable and energy efficient. 
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Quoted: Is it wet down there now or dry? dry I would recommend 6 mil plastic. It's far more durable than the 3 mil type. Not a lot more expensive either. More and more people are recommending that crawlspaces be sealed up. I'm planning to seal mine. Check out this site: Crawlspace Guide Or this one: Crawlspaces |
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Quoted:
Is it wet down there now or dry? I would recommend 6 mil plastic. It's far more durable than the 3 mil type. Not a lot more expensive either. More and more people are recommending that crawlspaces be sealed up. I'm planning to seal mine. Check out this site: Crawlspace Guide Or this one: Crawlspaces That's some good stuff. Thanks, Merlin |
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Quoted:
Go to your local builder supply, ilbt Lowes, Home Depot or other and get some Visqueen vapor barrier clear film 6 mil or better. You do not need pea gravel or a slab installed in a crawl space.
When you cover the soil in your crawl space, I suggest you leave a 2 to 4 inch pull back of the plastic film from the foundation perimeter and any support columns. This was suggested by my termite contractor. I did what they suggested and there is less condensation than before I ran the visqueen up to the foundation. In the first year after I installed the visqueen, I noticed more creaks in the floorboards throughout the house due to lower humidity in the house. One or two doorways are tighter and another sticks per the season. Overall, I think the house is more comfortable with the lower humidity. The insulation to the attic is a whole other story, that made our house much more comfortable and energy efficient. I almost posted this before too. Our house was built in 1849. It was built on columns of hand cut stone, log sills and floor joists, but basically, it was dirt. When we bought the house, we jacked it up, built a foundation under it, and set the house back down on the foundation. When I started researching plastic in the crawl space, the local guy who has been in the insulation business for about 40 years and who is known to be the "insulation expert" in the region, told me to put plastic down on only 2/3 of the ground for the first year––to leave 1/3 of the crawl space dirt exposed, THEN to go back in a year later and cover the remaining third. He said this was important in a very old house––to allow the wood to adjust to the lower humidity levels once I covered the dirt it had been exposed to for 150 years or so. This sounds like the same advice in a different form. And it's the first time I'd heard it other than from the old guy. I don't know how old a house should be before you apply this rule, or consider applying it. Ours certainly qualifies. |