Insulation

[wkashner]

A couple years back we installed under-the-floor radiant heating (oil, hot water) in our one floor northeast Pennsylvania (ranch) home.

Reflective insulation was installed to help reflect the heat up thru the floor. Now I learn that additional insulation should have been installed to create a dead air space to prevent the heat from warming the basement. The insulated but unfinished basement has its own in-floor heating zone but it rarely kicks on because of the heat loss from above.

I would like to install sheets of insulation, cut in ~15" widths that I can lay on the lips of the wooden I-beam floor joists. That way if I need to get in that ceiling for future projects, I don't have to deal with fiberglass insulation.

Any thoughts on what R value of sheet insulation would be correct for this type application?

 

[bnolte]

I got most of a 180' roll of Tek-Foam, a fiberglass and mylar sandwich I have left over from building my house. I believe this stuff is about R-6. How much insulation you put under the floor depends on a few variables. Do you want to keep the basement heated to room temperature, or just have enough heat down there to keep the pipes from freezing?

If you have thick carpet or heavy area rugs, these will have the effect of insulating the floors as well - in the wrong direction, which will push even more heat into the basement. The more insulation you put in your basement ceiling, the more heat will be directed up into your first floor living space. If you have say a nice 40 oz plush carpet over 5/8" foam padding, you might need as much as R-19 to get the majority of the heat where you want it, you can probably get by with less if most of your floor is tile or hardwood. As important as the R-value is, it is also important to make sure that you are truly creating a dead air space, batts tend to do that a little easier than rigid or semirigid foam, which can let drafts in through the cracks. Duct tape is your friend here.

 

[dcurran]

Hey Wayne, took notice your across the river from me. Small world! As far as your in floor goes, when the bubble reflective was installed, was it left about 2" inches down, or stapled tight against the floor? <- That makes a difference in conductive heat loss. Also, what temp are you running your in floor mixing valves at. Assuming you have 16" oc 10" I joice, the best methoid is having the reflective 2" down and finishing with unfaced R-19 15x48" fiberglass. Another option, not nearly as common, is to take 4' rolls of the bubble wrap reflective and running perpendicular to the floor joice. Sealing the seems with aluminium duct board tape. (not recomended for damp basements.)