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Insulation of non accessible floor space

needshave | Posted in Energy Efficiency and Durability on

I have a building that is historic in nature, built in 1896, pressed tin ceilings, 14′ ceilings hardwood floors. The floor is oak hardwood over 3/4″ pine/douglas fir sub floor over 2×12″. The floor is over a crawl space, sort of, and appears to be a dirt floor. This area is basically not accessible. There is nothing under there to access so to access it the floor has to come up. There is absolutely no insulation under the floor and in northern ohio, I need it.  How you recommend I insulate the floor and with what? Take up the floor and spray in foam insulation? Take up the floor, section rigid panels between joists, which would be so very time consuming, but Im at a loss. Any ideas?

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  1. burninate | | #1

    Don't know the best answer in this particular instance, but I need to point out that having poor energy efficiency because it's uninsulated & leaky can be a protective feature for a building exposed to moisture, since you're basically running a big clothes-dryer all winter long, taking in air, heating it up to low RH, and ejecting it after it's absorbed your household moisture. Perhaps this protective effect is why the house is still standing 124 years later without widespread rot. As a result, a degree of caution and testing is needed in retrofit applications like this, and it might be necessary to pair moisture-reducing approaches with insulation-raising approaches.

    What is holding up the house - what do foundation supports look like? Got any photos?

  2. needshave | | #2

    Its a two story brick structure, with an attached warehouse or garage. The warehouse has a concrete floor with 10' ceilings and is about 2100 square feet. I have all my toys in there. the whole building first floor, second floor and warehouse is 7800 square feet. I have added a picture of My wet bar area. The bar itself was built by my great grandfather in the early 1800's and I restored it and put in this room. Notice the wood floors and cabinetry. All would have to come up to insulate the area below the floor. I hate to do that.

  3. burninate | | #3

    Nice place.

    How high is the crawlspace? It is all open? Do you have any access from any direction?

    It might be easier to add perimeter insulation/airsealing to the crawl, and start conditioning it as living space - dehumification and heating with a little cross-ventilation to keep the moisture under control. To develop a ventilation plan you'd need to know that air will flow from one place to another, though, rather than being blocked by stem walls.

    1. needshave | | #5



      I have no access at all to the underside area of the floor, except for taking up the floor. It is closed except for two 8 x 12 ventlation grills ( one at the front and one at the rear on each side of the building in the outside wall. ( 4 in total) the center stem wall, has four grill that allows air flow from side to side. Below is another picture, showing the fireplace and cabinetry that is 20' long in the adjoining room.

  4. Expert Member
    Akos | | #4

    In this case it might be cheaper to insulate the crawlsapce from the outside. You also want a vapor barrier installed over the dirt floor, as long as you have enough space to crawl around, this is much easier to install than insulating the floor:

    It is also a good time to add in drainage around the foundation if you don't have any.

  5. needshave | | #6

    Thanks, I'm going to go back and read the article. Unfortunately I have no access to the crawlspace. Plastic vapor was my first thought, but I have to take up the floor to do that. The floor on the bar side is all oak. The floor in the fireplace is very beautiful southern yellow pine which will probably just splinter if I try to take it up. Not sure what it would do.

    If I was to take the whole floor, which I hate to do, should I consider expanding foam between the floor joists? I know that is very expensive and I know it will be difficult to deal with. ANy thoughts?

  6. user-1072251 | | #7

    Air sealing the crawl space - by installing and sealing a heavy plastic on the ground - and sealing the exterior wall either on the interior or from the exterior if need be, would have a larger effect than spray foaming between the joists. But if you want to add insulation, install a few inches of EPS under the poly on the ground. You get there by taking up a section of floor enough to crawl in; perhaps in an out of the way area, and leaving that section with a useable hatch for return visits.

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