Insulate behind basement stairs
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Is there anyway to insulate behind these basement stairs? Or would you just let it go? The builder stuffed fiberglass, but its way too compressed to be doing much. The basement is not finished yet, but I was planning on doing so in the future. This area under the stairs, however, would remain unfinished.
I also have no idea how to remove the stuffed in fiberglass. It is jammed up the tight spaces so if anyone has an idea of how to remove it, that would help.
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Are you trying to insulate the underside of the stairs, or the space between the stairs and the concrete wall? To insulate under the stairs, I'd use some fiberglass up into the underside of the steps, then polyiso sheets under the stair runners to enclose everything and add more R value. The polyiso would also act to support the fiberglass. You'd need to have a thermal barrier over the polyiso though, I'd probably use plywood here, but drywall could be used too.
If you want to insulate between the stairs and the concrete wall, rigid foam is really the only way to go. Fiberglass should NOT be used here, due to potential moisture/mold issues. About your only option is to slide cut strips of rigid foam up between the wood slats against the wall (it would have been much better to insulate first, then put the wood over the foam, but too late for that now). I'd use polyiso here unless you expect water issues, in which case I'd use EPS.
Note that the underside of the stairs is probably not going to be any big energy loser here, but it depends what your goals are. The drywall on the side opposite the concrete doesn't appear to be insulated, either, and if you really want to seperate the living space from the basement with insulation, you need to insulate the entire wall/ceiling assembly here, not just the stairs.
Bill
I'm looking to insulate the small tiny gaps between the stairs and the concrete. Could there be a mold/moisture problem if there is unfaced fiberglass shoved in there (you can see small pieces I pulled out laying on top of the brick on the ground in the first picture)? If so, any thoughts on how to get the fiberglass out?
Yes, you could potentially have mold problems using batts in there, faced or unfaced. You should be using rigid foam for those gaps. Your best option is to get some foam that is close in the thickness to the depth of those gaps, then cut pieces that you can slid up between the wood pieces that are there.
Bill
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I agree with Bill. A little-known fact, though, is that compressing fiberglass actually increases its R per inch value, up to a point, then it drops, but basically you don't have to worry about compressing it. You do need to worry about condensation, which is why foam is the best choice in this location.
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Thanks. Is the concern with unfaced fiberglass touching the concrete that humidity from inside the basement will pass through the fiberglass and hit the relatively cold wall and condense? Or is it moisture from the outside will penetrate through? For reference, the outside foundation has watchdog waterproofing by tremco.
Both, but especially the first. It keeps heat from the room from reaching the concrete surface but it does not slow air from reaching it. Foundation wall temperatures are often below the dewpoint so condensation can occur.
The screws and wood blocking is there only to reduce the bounce in the stairs. You can take those out and remove the wood blocking. This will let you now easily insulate with rigid.
If you find the stairs too bouncy, once the rigid is up, you can fasten 2x4s on flat to the rigid and run it down to the slab and support the stringer from bellow.
Looking to see if anyone has thoughts on a possible issue with sliding foam board between the studs.
Would there be any potential moisture/mold issues because the rigid foam has to be installed in pieces between the vertical wood framing? It's going to be impossible to have the foam air sealed to the wall. There will likely be small gaps at the edges of each cavity and obviously no foam board where there is wood. There would also be a small gap at the top where the foam board touches the bottom of the sill plate.
You slightly increase the chances of moisture getting into the wood when closing off the air spaces with rigid foam. The risk is likely minimal though if you have a dry concrete wall. The wood can still dry a bit to the interior if small amounts of moisture do get through periodically.
It's best to have the foam right against the wall in a continuous piece and then support the stairs off the floor or through the wall with periodic heavy bolts, but you can slide in foam with little chance of problems if you don't have a damp wall or bulk water issues.
Bill
Thanks for the advice!