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Community and Q&A

Insulating a crawl space

BvruVbRPJo | Posted in GBA Pro Help on

I recently bought a log cabin in N. H., zone 6. It is built on cement piers, completely open anywhere from 6 inches to 3 feet all the way around the perimeter. The water line from the well froze so I had an elecxtric ‘wire’ installed in the line. There is fiberglass insulation (one year old) under the floors with 3/8 inch plywood under that. The septic pipes run under the house in the open crawlspace. When I am at the house on weekends we heat with a wood stove. When we are not there we have a gas space heater (36,000 BTU) set at 50 degrees. The floor is only 40 degrees near the heater. The trap in the toilet and bathtub froze as well as some pipes. I planned on putting a plywood skirt with 2 inch rigid insulation inside the plywood around the house. After being up there this weekend when the temperature was below zero with a windchill of 25 below I wonder if that will be sufficient to keep the plumbing from freezing and the floors not quite so cold. The bathroom is about twenty feet from the gas heater. When I spilled some water on the floor next to the toilet it froze very quickly. Raising the house and putting a cement slab or basement is not really an option ($). Any advice beside just using it in the summer is appreciated.

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  1. wjrobinson | | #1

    Barry, In days of old, I winterized cabins. The high quality heat tape self regulates temp. Pressure treated skirt backed with foam sheeting is next, set down a ways into the ground if possible, not to be done till late spring.

    I have also made a system to blow out lines and empty traps for customers that come up rarely winters but want a quick way to water up and water down on their own. I use a hand bilge pump to empty toilet traps, and a few gallons of RV antifreeze per bath per winter this way. Not a great solution but works. The antifreeze can be used a few times according to some tight budget types.

    For more money there is a commercial system that automates water in and water out. Costly but works nice.

    You need to ultimately convert your cabin to a year round building by moving water lines to safe locations or bite the bullet and build a crawlspace that is well insulated.

    Speaking of frozen water, just thawed out a washing machine located in an unheated basement and am now on my way to checking 3 second homes that are rarely used winters here on the lake. Wish me luck.

  2. GBA Editor
    Martin Holladay | | #2

    Building an airtight, well-insulated, durable skirt is difficult but not impossible. You'll need to use pressure-treated lumber and plywood, and strive for airtight seams, using high quality caulk or gaskets. You'll get better performance with 4 inches of foam than 2 inches.

    There's no guarantee this will work, of course. Since your floor is "insulated" (ha) with fiberglass batts, there's no real reason to expect your crawl space -- even when protected from the winds by a new skirt -- to be any warmer than the great outdoors. To keep your crawl space warm, you'll need heat tape (or an electric resistance heater) as well as a good skirt.

  3. wjrobinson | | #3

    A nice local option for you Barry would be to visit a large trailer park and find out who is the expert at skirting mobile homes where you live. You would do well by working this angle as what they do for mobile homes is what you are asking about doing for your cabin. That is if you don't go the best but most expensive route of converting your cabin to a full blown year round home with frost protected insulated foundation.

    Another option someone did in your situation. Straw bales bermed around your cabin for a skirt to get your through winters for the least cost. Still, you need the heat tape but the bales have helped some. It's a scramble DIY solution but, "hay" been done that way by many.

  4. Brice Hereford | | #4

    4 inches of foam would be anywhere for R-14(EPS) to an R-26 with PolyIso. I am wondering if it would would help to put rigid foam on the ground under your cabin. In many of the new frost protected shallow foundations, they put rigid foam board outside of the walls, about a foot under the soil and angled out. As Martin says, there are no guarantees! This would help not just keep the cold air out, but would also help increase the insulation value on he gound level under the cabin.

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