I’m looking for advice on how to insulate the crawlspace ceiling of a 1960 single-story home in northern California. The house is 1375 sq ft with a flat roof, 3 beds/2 bath, and was built with no insulation in zone 3. The house sits on a carport and crawlspace (3-5′ high).

It’s impractical to condition the crawlspace because of significant gaps in the sheathing. I’m considering craft-back fiberglass insulation in the typical 2″x8” joists, but I’m not sure if that’s the best option. Spray foam would be fast but would hinder future wiring and plumbing changes, while rigid foam would be too much work to fit it securely.

What would you recommend? I’m open to any suggestions and feedback.
Thank you!”