How to Insulate the Sill With a Cinder Block Foundation

Homes built on cinder block foundations have a wooden beam, or sill, on top of each cinder block wall in the foundation. These can be clearly seen at the top of the interior walls in your unfinished basement, where wooden beams support the walls above and also attachment points for the ceiling joists extending across the top of the basement. The sills can be a major source of energy loss, causing a cold home that requires a lot of energy to heat. Apply insulation to the sill to improve the energy efficiency of your home.

Tape measure
Rigid foam insulation panels
Pencil
Straightedge
Utility knife
Construction adhesive
Caulking gun
Acrylic caulk

Instructions

- 1
  Start on the basement sill attached to the ceiling joists. Measure the height of the sill and the width of the exposed sill between the joists attached to the sill. Cut pieces of rigid foam insulation to match the measurements, using the utility knife.
- 2
  Apply construction adhesive to the backs of the panel pieces and place them onto the sill at the spaces between the joists.
- 3
  Apply caulk around the edges of each panel piece to prevent air seepage.
- 4
  Measure the length of the sill on the side of the wall without attached joists. Cut pieces of rigid foam panel to match the height, using the full length of the panel. Place the panel pieces onto the sill with adhesive and caulk as you did in the previous steps.

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