Below-grade guide

Before insulating a basement, review the water story.

A finished wall should begin with an understanding of the existing foundation.

In this guide

Describe what you can see
Define the intended use
Include the whole scope

Describe what you can see

Share signs of water entry, staining, condensation or past repairs. Insulation does not replace drainage work or repair a foundation leak. Have the underlying condition assessed before installing materials over it.

Define the intended use

A conditioned basement and an unconditioned basement can place the thermal boundary in different locations. Ask how the wall, rim joist and floor above connect in the proposed design.

Include the whole scope

Note the existing wall finish, ceiling access, approximate wall dimensions and any equipment that limits access. Ask which protective finishes, preparation and cleanup are part of the estimate.

Technical background: DOE — Insulating floors over unconditioned space. Sources checked October 20, 2026. General planning information; the project professional must verify product instructions and applicable local requirements.