The Problem:

Unsealed and uninsulated rim (band) joists lead to a number of problems.

• Unsealed - Air leaks through all the cracks between framing members and penetrations for plumbing and wires.  Air leakage accounts for about 40% of the heat lost in a typical building.  In addition small pests and insects often find their way in.
• Uninsulated - Heat from your basement or unvented crawlspace is lost through uninsulated rim joists.
• Condensation - Moisture condenses on the cold surfaces of rim joists leading to mold and rot.

(Common sources of air leakage through and around rim joists.)

The Solution:

Seal the sill plate to the foundation wall Seal the rim joist to the sill plate Seal the rim joist to the subfloor sheathing Seal all plumbing, wiring and other penetrations Insulate the rim joist Apply a vapor barrier to the interior side of the insulation

Fortunately, all of the above steps can be achieved in one easy solution.  Just apply closed cell spray foam over this entire area.  Be sure to cover all the seams to air seal and coat the band joist with 1-2 inches of foam.  Closed cell foam also creates a moisture barrier and helps prevent condensation.

(Cross section view of a rim joist after being sealed and insulated with spray foam.)

More Information

Learn more about the savings of sealing rim joists in this case study.