Replies

1. GBA Editor
   Martin Holladay | Oct 28, 2010 01:41pm | #1

   Frank,
   Your insulation contractor's suggestion will work.

2. 
   user-869687 | Oct 28, 2010 01:45pm | #2

   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.

3. 
   Riversong | Oct 28, 2010 05:27pm | #3

   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.

4. 
   pNJRiLZxNH | Oct 28, 2010 05:58pm | #4

   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

5. 
   Riversong | Oct 28, 2010 06:26pm | #5

   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 ¼" or so gap on all sides of the foam blocks to fill with the foam gun.

6. 
   pNJRiLZxNH | Oct 28, 2010 06:34pm | #6

   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.

7. 
   MICHAEL CHANDLER | Oct 29, 2010 11:46pm | #7

   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.