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Community and Q&A

How much basement floor insulation?

GBA Editor | Posted in Green Building Techniques on

I have a 60 year old home with a poured concrete foundation and concrete floor in the basement level. I’ve applied XPS foam board to the interior basement walls and I’m now considering insulated subfloor panels but figure I can do the same thing with thicker foamboard and sheets of OSB for less money per sq ft. However the panels seem simple to work with and would be quick and easy and they have drainage grooves that might be helpful, but I’m unsure if half an inch of XPS is enough. Is the convenience of these panels worth the higher price? Or is it just as effective to apply 1″ of XPS (or thicker?) to the floor and cover with OSB, anchored to the floor?

When applying either of these options should the seams and edges be taped, and sealed or should these small gaps be left, to allow moisture vapour to be pulled through the floor assembly by a dehumidifier?

I appreciate any help

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Replies

  1. jklingel | | #1

    If you don't get an answer here, search here (I know this has been discussed here) and see buildingscience.com. My question is "Is anything less than 1" of foam (if you have the head room) worth all the effort?" Were it me and I had the room, I'd add 2" of foam, tape the edges, and somehow "seal" the floor. I ain't a pro, though. Also, your location will help folks give advice.

  2. wjrobinson | | #2

    1/2" with drainage would work with thick carpet and heat to make a room in a basement. It will do nothing to lower your heating costs.

    Basically it is impossible to rebuild a home economically to save energy costs and have it payback. The only way it pays is if the home is free and you really only paid for the land when you purchased the property. And then the labor will have to be your own. If you pay a contractor to do a deep energy refit the ROI is impossible.

    So... if playing in green is your new hobby, then get to it. Otherwise, buy a green home built new IMO. Or downsize or move to a climate that needs no conditioning.

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