The house is drafty and cold. We are a couple miles from the Pacific so get a fair amount of rain and wind.

As long as the heater is running, it is nice. I'd like to improve it, however, I've also been warned to be carefully not to insulate it like a "new" house as these old ones survived for so long because they were drafty/allowed more air flow than new houses do. Using an IR camera, the exterior walls (looking from inside) are cold; especially at their bottoms. I think cold is coming in the bottom in the cellar and going up the walls. I'd like to insulate it if at all possible. Below is a picture I took in the basement looking up at the joists. Hopefully, I labeled the parts correctly. I was thinking of insulating that gap above the sill plate below floorboards.

Could anyone share what I might do here? I thought of packing it with mineral wool, Fiberglass, foam board. floor from basement

Also, I'd love to insulate under the floorboards between the floor joists too. Is that a good idea? If so, with what?

1 Answer 1


Sill plates and header (rim) joists are notorious for letting in cold air, particularly in windy climates and with older homes.

In modern day construction the sill plates usually rest on a membrane or gasket that serves to seal the opening between the sill plate and the basement wall. I would seal the opening there with a good caulk, some type of flexible silicone.

For the area behind the rim joist and between the floor joists, I would go with Rockwool insulation or else use insulating board (like XPS) cut for a snug fit and pushed into place.

  • 2
    A bead of spray foam around all the wood/wood and wood/concrete joints will ensure that the air infiltration is stopped before adding insulation.
    – FreeMan
    Feb 21, 2022 at 13:58

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