I'm going to be finishing my basement soon and I have a question about the joists. Here's my current plan just so you know:
Caulk the sill if needed
poly against the wall from grade level down
2x4 wood stud wall with unfaced batt insulation
poly sealing the stud wall with a little extra up top for next step.
Stuff the band joists with batt out to the stud wall and cap with rigid foam (cap is now flush with the wall below). Caulk the edges and seal the poly against it.

The question I have relates to fire code. The walls will be covered with drywall but what about little rigid foam cap between the joists? Do I need to cut a pattern in the top of the dry wall so it can slide right up to the subfloor or is it enough to leave that cap exposed because the room will have a drop ceiling? Or is there another way of covering the rigid foam?

Thanks!
Sean

 

Thats exactly how I did my own. Passed code. Several builders do it that way, that I have spoken to. I can't think of a better way to do it.

 

Which way? Leaving the foam caps uncovered by drywall and having the drop ceiling?

 

You have several problems:

1)Poly sheeting should NOT be placed over the foundation wall unless it can continue below the slab or into a periperal floor drain. The reason is that vapor condesing against the back of the sheet between the foundation and the poly will have no place to go but DOWN, and will cause water pooling, mold growth and wood frame rot...

The PROPER foundation vapor barrier is to coat the foundationw all directly with a vapor and water proofing coating such as DryLok paint or similar.

BOTTOM LINE: NEVER place plastic sheeting directly over the foundation wall unless the sheet extends below the concrete floor slab.

2) 2x4 stud wall is fine but it should be located several inches in front of foundation wall. Stud wall should be insulated with FACED fingerglass insulation to prevent interior living space air movement into the space behind the wall. Helpful link: http://www.extension.umn.edu/distrib...ng/DK7051.html

3) Fire Code. NO rigid foam insulation should be the framed wall or between joist spaces above. Installing such is a fire HAZARD.

Code require a minimum of 2x blocking to completley fill the joist spaces above any 2x4framed walls. Any openings can be filled with stuffed paperless fiberglass or exandable foam insulation. Rigid foam is flammable and never allowed unless covered completely with at least 1/2" drywall.

 

homebuild, your suggestions seem to conflict with another source I have on insulating.
How To Insulate
#1. I can see that, in the above instructions the poly comes out from the wall, the wall would be on top and not subject to rot. There is the question of moisture coming down and out still though. I can see the Drylok being a good alternative though and will consider it. Even both would work though maybe, in the off chance the concrete started to leak the poly would take it right to the floor where you could see it and not rot out the insulation and wall. Still, would have to rip out the wall section to fix it though.

#2. No need for faced because there is poly going on the wall between the insulation and drywall (see my plan, line 4). Was at the home depot the other day, they didn't sell faced, just unfaced and rigid.

#3. You can see near the bottom of the link where they tell you how to insulate between the joists using unfaced and rigid. It mentions later that rigid must be covered, and that was my question about how much. If I really want to notch the drywall I could cover it or maybe your last suggestion holds another idea.

Not sure what you mean about 2x blocking but it sounds as though you are saying to just stuff 2 layers of unfaced insulation into the joist area and no covering is needed?

Thanks a lot for the comments!
Sean

 

"Not sure what you mean about 2x blocking but it sounds as though you are saying to just stuff 2 layers of unfaced insulation into the joist area and no covering is needed?"

Nope.

You need to install at least 2x10 blocks (or similar) between any 2x10 (or similar) floor joists above any framed wall in a basement and between any joists above it.