In new construction, insulation should be installed at exterior wall band joists?

• A. Only inside finished walls
• B. At exterior wall band joists (as required)
• C. Only in the attic
• D. Only around windows

Answer: (B)

Insulation around the exterior wall band joists is needed to stop heat from leaking through the rim where the floor framing meets the wall. That band joist can be a weak spot, creating a thermal bridge that bypasses the wall insulation. By insulating this area—often with batts snugged into the joist bays and sealant or spray foam around the rim—you create a continuous thermal envelope and reduce drafts, condensation risk, and energy loss.

So, insulating at the exterior wall band joists (as required) ensures the whole wall assembly is properly insulated, not just parts of it. Insulating only inside finished walls would miss the rim area, insulating only in the attic would not address the wall edge, and insulating only around windows leaves the band joist uninsulated.