Garage Addition

Wayco Wayne

Customer wantsw radiant floor heat. contractor has already put floor joists in allowing for 3/4 sub floor and 3/4 hardwood floor. No time for warmboard, job is wanting to move. Contractor is going to fill the bottom of the floor with concrete up to 1 inch up from the bottom of the floor joists. He says it firms up the floor. The floor joists are 2 x 8's. He comes up 1 inch that leaves 6.5 inches. He wants to insulate with 4 inches of styrofoam in between the floor joists and then put in tubing and pour concrete over the last 2.5 inches. Sounded OK to me at first but started thinking. The heat from the top concrete could travel down the floor joists into the lower concrete. Whats a better way to do this? Could I build in plates into the sub floor? Does anyone have any pictures of this? Why can't contractors call you before they get this far? WW

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eleft_4

What's the purpose of the 2X8s? nm

Wayco Wayne_2

The addition

is being built over an existing step down from the house garage floor. The joists are to raise the level of the addition floor to the same level as the house. The space below the joists are to filled with concrete up to and covering the bottom inch of the joists to solidify the floor. Wonder if I could wrap some foil bubble stuff around the bottom of the joists to insure the heat would only go up through he hardwood floor, and not traveling down through the joists into the concrete below the joists. Am I worrying too much ???

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Steve Bergerson

I wouldn't worry..

I looked up the R-value for pine, and came up with about 1.5 per inch. Assuming you have 4" of joist embedded in the concrete, the r-value of the joist to the bottom of the slab would be 6.

If you remember reading anything from Dan's books, remember that heat is lazy, and is going to take the easiest path. Once your tubing is in, and the filnal slab is poured, and the finished floor is layed on top of the slab, you will have heat transfer by conduction with a large surface area (the floor), that has a relatively low r-value.

Compare your radiant panel (the floor) with the path of the joists... A much smaller path for heat, with a much higher R-value.

Although there may be some heat transfer through the joists, I don't believe it is enough to worry about insulating them further. Run the calculations yourself for your job, and make sure it is easier for the heat to go up than it is to go down...

Have Fun!
Steve

eleft_4

WW,
You have a Rube Goldberg to start with. Pour the concrete minus your foam, sleepers if needed, warmboard and finished flooring. The joists seem redundant and are inviting bugs in the future.

"measure twice cut once" al

Wayco Wayne

Thank you Steve

You are absoluetly right. I looked up the R value for the sub floor and the hardwood. Together they amounted to R1.5. And if the joist distance is 4 times 1.5 the R value of the joists is 6. It will definetly go where I want it to. :)WW

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