Replies

1. Expert Member
   BILL WICHERS | Oct 06, 2021 10:45pm | #1

   It would be good to start by turning off caps lock. We're friendly here, no need to yell at us :-)

   "Blue board" is usually Dow Chemical brand XPS. If it was pink, it would be Owens Corning brand XPS. Pretty much the same material either way. 2" XPS is rated R10, a little less than that after it's fully aged. 6 inches wll be R30. That's preatty reasonable.

   You would want to put it directly against bottom of the joistsif you can. You could also put it under any sheathing that might be under the joists, depending on how your place is constructed. The underside of the joists is preferable (no thermal bridging that way, and less installation labor). You'll want to install the sheets with the seams staggered for best results. You can get large plastic "insulation washers" that will help to keep screw heads from pulling through the foam when you install it.

   You could put a coat of Coppercoat on the underside of the flooring, or a mold killing primer (Zinsser makes one).

   Bill

2. 
   Mark_Nagel | Oct 07, 2021 06:34am | #2

   The general rule is to maintain a warm pocked under the floor (joist cavity) in order to protect water lines (drain lines as well*) and furnace ducting. If you're in a cooling zone then it's less of a concern.

   * These are less prone to freeze issues owing to their size and that there's usually enough warmer materials routed through them.

   Be sure to account for dealing with rodents and such. If you cannot guarantee that they'll stay out of your crawlspace then you need to watch out that they don't find ways through that insulation and into the cavities (the standard belly wrap is fairly hardy in this regard, though I don't have any firsthand experience in these dynamics). Set traps or such as added insurance: I wonder whether having bait is but an encouragement for attracting critters in the first place; however, when it's cold the leading attraction is warmth.

   Also, you'll probably want to be sure to mark plumbing locations in case you need to locate any leaks.

   A big tip that I've learned, and is stressed here, is that crawlspaces are things to avoid (can't readily do with manufactured homes, though).

3. 
   audiodoctor | Oct 07, 2021 11:00am | #3

   Thanks-- ok .. if i put the blue board against the joists- i will have a 8 inch space from the bottom of the floor to the blue board. I will do it that way
   my eyes are not like they used to be that's why i used caps ..

4. 
   audiodoctor | Oct 10, 2021 04:37pm | #4

   I just talked to a home owner up the street. they put 2 inch blue board all around the home == covering the skirt AND VENT HOLES . there was a LOTTTT of mold underneath and what looked like green pond growth on the cement slab.. . so they took off the blue board..