I get the focus on rim joists, but honestly, I’d argue for at least some wall insulation even in an unfinished basement. We did just the rim at first—helped, but the floors still felt chilly. Once we added a layer of mineral wool to the walls, the difference was way more noticeable. Plus, it’s not just about comfort—less heat loss means lower bills and a smaller footprint. Sometimes the “best bang for your buck” is a bit broader than it seems...
Funny, I had a similar experience—sealed up the rim joists thinking that’d be enough, but those basement walls just radiated cold. Ended up using rigid foam panels on the walls and it made a bigger difference than I expected. Did you run into any moisture issues after adding mineral wool? I’ve heard some folks worry about trapping humidity behind insulation in basements...
I totally get what you mean about the cold just seeping through those old basement walls. I tried mineral wool too, mostly because I liked the idea of it being less “squishy” if things ever got damp. Haven’t had any real moisture issues yet, but I do wonder sometimes if I’m just lucky or if the old stone foundation is breathing enough on its own. Did you tape your foam seams? I’ve heard that can make a difference with condensation, but honestly, I’m never sure if I’m overthinking it or not...
I’ve gone back and forth on the whole taping foam seams thing, honestly. On one hand, taping does help create a more continuous air barrier, which can cut down on drafts and slow down any potential condensation forming behind the insulation. But then you start reading about old stone or brick foundations needing to “breathe,” and it gets a bit murky. I’ve seen some folks argue that if you seal everything up too tight, you might trap moisture where you don’t want it, especially in older homes that weren’t built with vapor barriers in mind.
When I did my basement, I ended up taping the seams with foil tape, but I left a small gap at the bottom near the slab—just enough for any incidental moisture to escape if it ever showed up. Not sure if that’s textbook, but it felt like a decent compromise. Haven’t had any issues so far, but I’m always half-expecting to find some weird science experiment growing behind the foam one of these days.
Curious if you did anything special around windows or rim joists? That’s where I always seem to get stuck—those odd angles and gaps are a pain to insulate properly. I tried using spray foam in the rim joist cavities, but it’s messy and not exactly cheap. Sometimes I wonder if it’s overkill, but then again, those spots are notorious for letting in cold air.
And about mineral wool—totally agree on the “less squishy” factor. It holds up better if there’s ever a bit of dampness, though I still get nervous about long-term moisture. Did you put any kind of vapor barrier over the mineral wool, or just leave it exposed? I’ve heard conflicting advice on that front too... Some say it’s essential, others say it just traps moisture.
It’s wild how much nuance there is to insulating old houses. Every time I think I’ve got it figured out, someone throws another variable into the mix.
I get where you’re coming from, but honestly, I’m not convinced leaving a gap at the bottom is the best move. In my old place, I tried something similar and ended up with a musty smell after a wet spring—turns out moisture found its way in and just hung out behind the foam. Since then, I’ve gone all-in on taping and sealing, then just making sure there’s good dehumidification down there. Around rim joists, I swear by rigid foam cut to fit and sealed with canned spray foam—even if it’s a pain, it’s the only thing that really stopped those cold drafts for me. As for mineral wool, I usually skip the vapor barrier unless it’s a really damp basement—otherwise, it just feels like asking for trouble with trapped moisture. Every house is its own beast though... what works in one can totally backfire in another.