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Closed-cell foam insulation

user-728920 | Posted in Energy Efficiency and Durability on

We own a century home which over the years has sunk into the ground so there is little or no crawl space. In order to insulate the ground floor, I would like to tear out the old oak tongue and groove flooring, cover the subfloor with a vapor barrier and then fasten 2x4s to the subfloor and use closed cell foam to insulate. Does this sound like a feasible plan?
Chuck Pemberton

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  1. user-2310254 | | #1

    Charles. I suspect there are better options for insulating your ground floor. But would like to know more about your sinking foundation before suggesting anything. Have you had an engineer or foundation specialist determine what is causing your problem?

  2. Jon_R | | #2

    The plan is to then put the oak back down?

    An odd but perhaps interesting point: at somewhere around 12" of foam underneath, a typical house will float. Ie, it can support itself on completely unstable soil.

  3. GBA Editor
    Martin Holladay | | #3

    You haven't described the situation well enough for us to be able to give you advice.

    What type of foundation does this house have? Is it on posts, or is there a perimeter foundation of concrete or stone masonry?

    You wrote that there used to be a crawl space. Has the house settled so much that the subfloor is touching dirt? Or is there a vertical crawl space of some kind? If there is some type of crawl space under your subfloor, how high is it?

    Needed repairs might include the following:

    1. Consulting with an engineer to determine how to retrofit a stable foundation under the house.

    2. Lowering the grade at the home's perimeter (to keep the wooden components of your house safe).

    3. Constructing a trap door in your floor so that you can excavate and remove the dirt in your crawl space.

    These are just possibilities... It's hard to know what type of work your house needs unless you describe it more fully.

  4. user-728920 | | #4

    The house has a perimeter foundation of stone with no footers underneath. From what I've been able to see by digging test areas around the foundation, there are some stone pillars underneath as well. Some are still good while others have fallen over. Yes, the house has settled so much that what ever crawl space was originally under the house when it was built in 1912 has reached the point where there is about 6" of space between the bottom of the floor joists and the dirt. Under some points, the house has settled so much that the bottom of the floor joists are touching the dirt underneath. From what I've been able to determine, the dirt is completely dry under the house. The house is a two story farm house with a footprint of 40' by 40' with three chimneys for fireplaces coming up through the house and roof. There are also two porches, one is 10' by 40' and the other is 5' by 20'. Both are attached to the house. Both are built on wooden posts. And to answer an earlier question, I would be replacing the torn out oak flooring with wide board pine flooring to add to the character of our home. I am hoping to find a method of adding a vapor barrier and insulation that I can do myself. Even with dehumidifiers running in the warm months, we find mold growing on furniture and shoes. The house has no central heat or ac, instead we rely upon propane heaters in some rooms, base board heaters in others, and small oil filled radiators . I have talked with local contractors and spray foam installers and none of them would be willing to undertake the digging the crawl space out by hand. I hope this better explains our situation.

  5. user-2310254 | | #5

    Chuck. I'm surprised you've had so much settlement without it affecting your chimneys, utilities, and door and window openings. If you plan to stay in the home for some time, it would make more sense to sort out the foundation issues before doing anything else. You may need to jack up the house and install a new foundation and unvented crawlspace.

    Also... Where are you located?

  6. srenia | | #6

    Ran into a similiar issue a while back on a older house. The crawl space being filled in with dirt wasn't caused by settlement in my case. Just water carrying dirt into the crawl space. The easiest method I found for fixing settled floors is rid up the old tongue and groove. Save the wood for other projects or give it away. Sister the joist and put new subfloor on. Any digging and structural issues are easy to spot and fix on that time.

    If you jack and dig under the property it can sort of work. The problem with that technique is that you waste a lot of time. The results are that the floor is still not perfectly level, you miss issues and it cost more. The costing more might confuse you. Been there, done that. The floor joist sistering is cheap, the subfloor varies on pricing but not that expensive. Being able to dig out the dirt in day verses months is priceless. Putting a vapor barrier is a great thing. Be careful on foam because insects love to make nest in them. Could cause more issues than not. Putting rockwool on the crawl space walls will give a better return.

    Good luck. So many ways to fix issues. Sistering joist and putting new subfloor is something that has worked great for me verses other measures.

  7. GBA Editor
    Martin Holladay | | #7

    Like Steve Knapp, I would advise you to investigate the settling issue more before proceeding with repairs. It's possible that your house is settling, as you suspect, or that flowing water has brought silt into your crawl space, as Stephen E. surmises, or both. But I can't imagine investing in new insulation, subflooring, and flooring without determining what's going on and doing remedial work.

    Stephen E. is right about old houses with uneven floor joists -- the best solution is to sister new floor joists, perfectly level, to the old joists. Removing the existing subfloor will give you an opportunity to remove dirt from the crawl space to lower the crawl space floor, and then to install 6 mil poly over the dirt. If you can do all that, the best place to install new insulation (probably closed-cell spray foam) would be on the interior side of your foundation walls.

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