How do I insulate this wall?
4A home was originally a late ’30’s summer house that’s been sorta winterized and had several big renovations. There is a downstairs room (under a deck) with 3 exterior walls. Northwest exposure to wind and weather. The room is unpleasantly (unbearably) cold in winter. House is on piers with closed crawl.
we had the two single pane windows replaced and haven’t trimmed them yet, and this weekend after a long drenching rain found a leak above the window. (This is probably from the roof under the deck, something we will address.) I have been prepping the room to paint and saw that the drywall under the window has water stains. I have read that insulation that’s gotten wet needs to be replaced, so busted out the drywall under the window and now trying to understand how to proceed.
Layers from the outside in: cedar siding, 1″ blue foam-board that butts (not taped or sealed) to furring strips that were evidently used to nail the siding to, original roughcut clapboard siding, some kind of ancient fiberboard maybe celotex?, and then 3.5″ R-11 fiberglass batts in the wall cavity with the kraft paper side facing the room. What’s very strange to me is that I can stick my hand in the wall cavity and feel a big air space underneath the baseboard. There was a bunch of compressed fiberglass jammed into that space.
The insulation didn’t seem damp, but I wonder if the gap under the baseboard is what is making the room so cold. Considering tearing out drywall in the whole room (ugh), but only if I can make substantial improvements. We are in a very humid area so that is a concern as well as weatherproofing and air sealing. Not to mention don’t have a ton of cash to throw at this. I just want to know the ‘right’ way to insulate/seal this wall, and then see if I can muddle my way through.
Any thoughts? what do you think of replacing the fiberglass with foam board and sealing the joints and gap under the baseboard with canned foam? Should I be worried about condensation since I would be basically sandwiching the clapboard and fiberboard between two layers of foam? Do I leave the fiberboard alone? If I remove that too I have 5″ to work with instead of 3.5″. Or do I just put things back the way they were and see if I can insulate the rim joists in the crawl and call it a day. Could really use some help here!
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Replies
Can you post a picture showing the window from the exterior?
The 1" XPS is sufficient for dew point control at the sheathing layer only for US climate zones 1 through 5. Where are you located?
It's not clear to me exactly where that gap is- under the floor? ...under the exterior sheathing ?
The brown edge of the batt is a sign of large amounts of air movement- was that at the bottom plate of the studwall?
Has the window flashing been inspected/verified as being lapped correctly?
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I think you are wasting your efforts looking at the bottom of the wall until you fix the roof /wall leak and can keep the water out of the wall air sealing and insulation are pointless as the wall will soon rot or mold to the point it will be necessary to replace the wall.
Once you have dry wall then you need to determine where and how air is moving thru your wall only then is it worth thinking about insulation.
To understand the air flow you will need a blower door or some fan to move air thru your walls.
Walta
Just to be clear, we will find and fix the leak, although all of your comments are very welcome. My question is how, and whether or not we should, try and improve insulation in this freezing cold room.
According to the map I'm in 4A, southern Maryland. The window leak is at the top of the frame and I believe means the roll roofing under the deck has/is failing. Similar leak on the adjacent screen porch. We'll check on the flashing first but probably have to call a roofer. The brown edge on the fiberglass batt is crumbs from the fiberboard. I think it's years of air coming under the sill of the old single pane windows. I plan to foam under the sill.
I don't know how to explain the airspace under the baseboard. It's under the baseboard and above the subfloor. It's like the baseboard was toenailed, I can run my hand underneath it from inside the wall cavity. At some point the room had knotty pine paneling, and we installed the hardwood floor twentysome years ago. I still don't know if that gap explains why the room is so cold.
D.,
Your first step is clearly to fix the roof. No work should be done in the room below until the roof is fixed.
Needless to say, if this room has a flat roof with a walkable deck above the flat roof, the roof is hard to detail. Lots of builders get the details wrong. So make sure you hire a competent roofer.
Once you've installed a new roof and paid for the work, you can address the walls below.
Your description of the exterior rigid foam is a little unclear, but it sounds like you have 1-inch-thick vertical furring strips, with narrow rectangles of rigid foam inserted between the furring strips. Is that correct? If so, that's unfortunate -- because a continuous layer of rigid foam, with furring strips on the exterior side of the rigid foam, would do a better job of reducing air leakage.
How to proceed depends on your budget. I'm guessing that the window rough openings lack window flashing, so the best way to proceed would be to remove all of the windows, install flashing in the rough openings, and then re-install the windows (or install new windows).
If you have no plans to replace the siding, the best way to air-seal the wall would probably be a flash-and-batt job. For more information, see "Flash-and-Batt Insulation."