Under Radiant Floor Insulation
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| Posted in Energy Efficiency and Durability on
I have to insulate between the main floor and basement. The main floor is 2″ concrete with radiant pex tubing. The Insulation contractor suggested a radiant barrier along with batts under the main floor between the joists to help direct the radiant heat upwards. Is this any truth to this claim? Are there best practices for insulating under suspended slab?
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Replies
Frank,
Your insulation contractor's suggestion will work.
Do you want to heat the basement with the main floor's heating system? If it's a conditioned space in constant use then you could let the radiant system heat in both directions. If not then it's better to do as the contractor suggests.
Frank,
If the basement is unconditioned space, then you need insulation between the two spaces. If the basement is conditioned space and you just want to direct the radiant heat upwards toward the floor surface, then you need a radiant barrier.
If you install staple-up foil/bubble/foil between the floor joists 4" below the subfloor, this will not only prevent radiant heat loss downward but also provide almost R-9, or the equivalent of almost 3" of fiberglass insulation.
You could do both, but I would keep the radiant barrier at least 2" below the subfloor.
Thanks all. The space is an unfinished basement used for laundry/storage/kids toys/bike trainer. I intend to keep it as cool as possible. That said, it sounds like a radiant barrier 2" below subfloor w/ ecobatts is the correct course.
It's also been suggested I foam the rim joist. However, the cost is very high.
Couldn't I achieve the same air seal and R value for the Rim joist by air sealing using a foam gun and then using batts OR rigid against the rim joist?
thank you
Frank,
Cut slightly undersized pieces of 2" XPS foam board, fit them between the joists, sills and subfloor, and then use low-expansion foam in a gun to "caulk" the gap around the edges. You'll get a better seal with less mess if you leave a ΒΌ" or so gap on all sides of the foam blocks to fill with the foam gun.
Thanks Robert...I have a $1800 bid in front of me to foam the rim...that should buy plenty of rigid board and foam...and a few sets of latex gloves.
The 4' x 8' x 2" R-12 Poly-iso "Hunter panels" are going for $26.00 at ABC supply. Check to see if they have a branch near you. great price if a bit messy to cut as you can't use a hot knife, we use a portable table saw.