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stmbtwle

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Reply with quote  #31 
I think a lot of it has to do with the thickness of the plastic, more than the plastic itself. The only time I've had problems is with regular pop or water bottles and 1gal milk jugs, both of which are pretty thin. Commercial containers are a lot thicker, and designed to last a lot longer.

Could also be that the pressure in pop bottles weakens the plastic, and makes it more permeable.

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JC77

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Reply with quote  #32 
Hey power gripe, I had this exact same issue at my house. My house is in central Illinois so plenty of hot and cold weather. Your crawlspace has vents because of the damp earthen floor. During times of rain, the earth outside your home becomes wet along with the dirt around the edges of your crawlspace or the entire crawlspace becomes saturated (I've seen water standing in crawlspaces!) depending on how well your site drains. Some crawlspaces stay damp year round. In my crawlspace, the dirt in the center would stay dry but the dirt near the edges would become really wet as it absorbed water in wet weather. This moisture will wreak havoc on your joists and subfloor. The vents should remain open in the summer and closed or barely cracked open in the winter. The floor above the crawlspace should be insulated well (foil faced and high R value) and sealed from the moisture/humidity of the crawlspace. Treat the floor above the crawlspace just like any other exterior wall of your home minus the siding.
     You do have options though. You can close up the vents but you need to put a heavy vapor barrier down over the dirt to seal off the moisture. You can use a heavy (8mil or thicker) plastic. Lay the plastic down and tape any and all seams. You can insulate the floor if you want but it's not necessary. Then tape the plastic to the walls of the crawlspace with the intention of keeping all the moisture sealed under the plastic. Then I'd insulate the walls of the crawlspace. I had mine spray foamed but only because the outfit that did it was having a big sale so I got it done cheap. The spray foam doubled as an adhesive to seal the plastic to the crawlspace walls. Otherwise, you could cut 2 inch thick polystyrene panels into strips that fit through your crawlspace door and glue them to the (block?) walls. The more insulation the better. Don't forget the rim joist either.
     Once you have the floor sealed and walls insulated, you can seal off your vents but you still have to provide some kind of ventilation or air supply to the space. If your crawlspace opens into your home, you could leave the access door open or maybe put a screen over it. I have forced air ducts in my crawlspace so I made a small hole in my main trunk so a small amount of fresh air is pushed in. Mine has been this way for about ten years without any issue. The main idea is that if you choose to seal it off, you need to treat the space like any other conditioned interior space in your home. I'm not sure if there's a formula for figuring the proper amount of air but the space needs to breathe a little. From the sounds if things, just doing that alone will cut your bills. The little bit of air I intentionally lose out of my duct work was not even noticeable on my bills as the savings from insulating and sealing more than made up for it. If you seal off the vents from the inside, make sure to seal them from the outside as well so a driving rain cannot push water in. I put a hardwood floor over the top of a portion of my crawlspace about seven years ago and so far it has been fine. No boards have warped or joints split so I'd say my crawlspace sealing is working ok. 
    Sorry this is so late. I just joined and have been slowly reading my way thru the posts. I saw this and had to share. I spent a considerable amount of time trying to figure out how to do this to my crawlspace. The floor above my crawlspace was already insulated with foil faced batts stapled up between the joists. The spray foam guy had me remove the batting a few feet from the exterior walls so he could spray the rim joist. This also allows some heat to escape from the floor above down into my crawlspace. Any time I've opened the access door to my crawlspace, there's never a musty smell or any evidence of a moisture problem nor is there some huge temperature difference. There is no drain in mine so a burst pipe would be pretty nasty. I put a wireless humidity monitor and also one of those basement water alert gizmos in there. It's supposed to give off a loud alarm if it ever detects water. So far, all I've had to do is replace the batteries. I also educated my family on how to shut the water off if they hear it when I'm not home. For what it's worth, I would never own another house with a crawlspace. I'll be in there again soon putting pex under the tiled portion of the floor for a radiant floor heating system. Ugh. At least my boys are old enough to help this time.
     Since you mentioned your floor above the crawlspace is not insulated, I'd think adding some kind of heat storage to your crawlspace after sealing/insulating would be beneficial. Or maybe seal it and insulate it first and see how cold it gets in there in the winter. I have two heat sources available to my crawlspace (the floor above and the furnace ducts) so mine doesn't get cold at all during the winter. If yours still got cold after sealing/insulating, some of the heat stored in the crawlspace would be lost to the crawlspace but I would think the overall effect would still be a benefit. The best kilowatt hour out there is the one you don't need in the first place. Since you mentioned trying to use the space for heat storage, I'd probably make some effort to insulate the entire floor of the crawlspace or at the very least put foam board insulation underneath whatever you use to store heat with. The ground around the exterior edges of the crawlspace will get pretty cold in the winter because the ground outside will likely be frozen so maybe some insulation on the floor around the edges would be the way to go if you didn't want to insulate the entire floor. I'd seal off the moisture first and put the floor insulation on top of the plastic so you lessen the chance of poking holes in the plastic while you're crawling around but it could be done either way. Extruded polystyrene could lay directly on the dirt and be ok in this case.
     If you decide against heat storage in your crawlspace, I'd at least place foil faced insulation of the highest R-value I could afford up between the floor joists and maybe staple up some plastic over that for an additional moisture barrier. Then, you could glue foam board to the crawlspace walls in the future for another layer of insulation in the winter and monitor the crawlspace. If it were dry and extremely cold, I'd close off the crawlspace vents and only open them when there was a need for airflow. Although if you are going to that much effort, it's probably best to just seal it up anyway.  My cousins house has a concrete floor in his crawlspace with a floor drain. Much nicer way to do a crawlspace!! I see this was all posted about a year ago. Have you made any progress?
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