That sounds about right—older houses just don’t behave like new builds. I ran into the same issue with spray foam on a 1920s place... too tight, and suddenly there’s moisture where you never saw it before. Backer rod and sealant is a solid call, keeps things flexible and doesn’t lock in trouble. It’s a bit of trial and error, honestly—sometimes what works for one window makes a mess on the next.
I get where you’re coming from, but I actually lean a little more toward using low-expansion foam in spots—just not the way most folks do it. The trick with these old houses is to go super light and leave a bit of breathing room, instead of packing every gap tight. Done carefully, it can cut drafts without turning the whole wall into a vapor trap.
That said, I’ve seen backer rod and sealant work well too, especially on those wonky window frames that are never quite square. It’s just... sometimes that combo doesn’t block sound or cold as much as people hope, at least in my experience. Had a 1918 bungalow where I ended up mixing both methods—foam for the big gaps (but only a little!), backer rod and sealant for the rest. Still had to keep an eye on humidity though, like you mentioned.
Honestly, there’s no perfect answer. Every window’s got its own personality in these old places. Sometimes you just have to try something and see how the house reacts.
- This is super helpful, thanks for sharing your experience. I always thought more foam = better, but I guess that’s how you end up with a wall that sweats like it just ran a marathon.
- Love the “every window’s got its own personality” bit—mine are definitely all drama queens. One’s always drafty, one sticks, and one just kind of... sighs when it rains?
- I tried the backer rod/sealant combo on my kitchen window. It did help with the cold, but sound still gets through. Maybe I was too stingy with the foam.
- Didn’t even think about humidity until I saw some weird paint bubbles last winter. Now I’m paranoid about trapping moisture.
- Seems like there’s no magic fix. Appreciate knowing it’s normal to mix and match and not get it perfect the first time. Makes me feel less clueless when I’m staring at a 2-inch gap and a tube of caulk wondering what could possibly go wrong.