Insulation for New Construction: Spec Checklist

Code minimum vs. high performance

2021 IECC requires roughly R-49 attics, R-20 walls, and R-30 floors in most climate zones. Code minimum is the floor, not the goal — adding 2-3 R-values in the walls and pushing the attic to R-60 typically adds <$0.50/sq ft to a new build.

What to spec

Attic: R-49 to R-60 blown cellulose with full air sealing of the top plate and penetrations

Walls: R-21 batts or R-23 dense-pack cellulose, plus R-5 continuous exterior rigid foam

Crawl space: encapsulated with R-15 closed-cell spray foam on foundation walls

Rim joist: 2" closed-cell spray foam (one of the largest air leak points)

Blower-door target: ≤ 3 ACH50 (code is ≤ 5 ACH50 in most zones)

Contractor questions

Can you provide a blower-door test result after rough-in?

Do you air-seal before insulating, or does the framer handle it?

What's your QA on spray foam thickness and temperature at install?

Will you supply manufacturer specs and warranty in writing?