We have very cold floors in the kitchen because the outside air is moving up through the external cantilevered floor.

I'd like to insulate it by cutting 2" foam (probably XPS or Polyurethane) and attaching it between the joists. Note: house is in San Francisco (lowest temp is about 38F) Three questions:

  1. Is this a good approach? (better ideas welcomed)
  2. Do I need to worry about moisture buildup?
  3. What's the best foam for the job?

Photo of my joists: enter image description here

Proposed solution: enter image description here


Any kind of insulation will help us would consider boxing by in the space also, if in an elevated area we used to have trouble with swallows building their mud nests in areas like that so boxing them was a must, (I don’t see that issue here but we had it just north of you). But insulation will help.

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