How to Caulk a Rim Joist

The rim joist is the rim board across the perimeter of your home's foundation or basement where the ends of the floor joist connect. This is an area where there is a lot of heating and cooling loss. It is also difficult to insulate and caulk a rim joist due to the many pipes that run through different areas of it. Caulking a rim joist is best once you place some rigid foam insulation against the joist between the floor joist.

Rigid foam, 2-inch thick sheets
Utility knife
Silicone caulk
Caulk gun
Spray expanding foam insulation

Instructions

- 1
  Measure the height of the rim joist with a tape measure. Take another measurement on the face of the rim joist between each floor joist.
- 2
  Cut pieces of rigid foam to your measurements with a utility knife. These pieces will fit against the face of the rim joist in between the floor joist. Repeat for the entire perimeter of the home. Cut the rigid foam as necessary to fit around pipes and other obstructions going through the rim joist.
- 3
  Apply a bead of silicone caulk around the seam between the rigid foam and rim joist with a caulk gun. Caulk around all four sides of the foam where it meets the sill plate and floor joists.
- 4
  Fill gaps between pipes and the rigid foam with spray expanding foam insulation. Spray the expanding foam insulation into seams between two pieces of rigid foam where you fit the foam around obstructions.

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