Air sealing seems to get overlooked. People focus on R-value but skip the caulk and foam around windows, doors, and top plates. That’s where a ton of heat actually escapes.
Totally agree—air leaks are the real wallet-drainers. I once spent a weekend chasing drafts with a smoke pencil and a tube of caulk and saw more improvement than after stuffing every stud bay with insulation. Old plaster walls? Unless you’re gutting, I’d rather put my energy in the attic and crawlspace too. Less mess, better payoff, and you don’t have to learn how to patch 1920s horsehair plaster... which is a dark art I never want to revisit.
I get the focus on air sealing—definitely a big deal—but I wouldn’t write off wall insulation entirely, even with old plaster. Dense-pack cellulose can be blown in from the exterior or attic with minimal patching, and it really helps with both drafts and sound. I tried just sealing and attic work in my 1940s place, but the walls still felt cold in winter. Sometimes it’s worth biting the bullet, especially if you’re already doing siding or roof work. Just my two cents...
I hear you on the wall insulation—sometimes air sealing just isn’t enough, especially in those older homes. I did dense-pack cellulose in my 1920s bungalow when we replaced the siding, and it made a noticeable difference. The rooms felt less drafty and the heating bills dropped a bit. It’s definitely more work, but if you’re already opening things up, it’s worth considering. Cold walls can really suck the comfort out of a place, no matter how much you seal up the attic.
Honestly, if you’re tearing off siding anyway, dense-pack cellulose is a game changer. Last time I did it, took me and a buddy about three days for a small house—mostly because we kept arguing over who got to use the hose. Worth every minute once winter hit.
