Mind the Gap

Window frame with spray foam

I enjoy working on projects around the house. But one DIY project often leads to another. While removing some old paneling this summer I uncovered an ugly secret hiding behind the window trim. I discovered a 1"+ gap between our newer double pane windows and the wall framing. Loosely coiled foam strips were the only insulation in the window to wall air space. It's no wonder the window frames felt so cold last winter!

Our home has double pane, horizontal sash windows that seal well and should provide decent insulation with the view. They would have if not for carelessly installed insulation that allowed air circulation and thermal bridging. So, I made a trip to the hardware store and picked up a few cans of gap-filling spray foam.

Here are my notes on using canned spray foam insulation:

  • Wear disposable gloves, spray foam sticks quite well to skin!
  • Gauging how much foam to spray takes practice. It may take a can or more to learn how much the foam expands.
  • Spraying the foam too fast can leave holes and blow the foam out of the gap.
  • Have a rag and acetone ready to clean up any stray foam before it sets.
  • Masking tape on adjacent surfaces makes clean up of excess foam easy.
  • Wait for the foam to fully cure before cutting or trimming any excess.

I wasn't thrilled, or very shocked, to find more holes in our home's thermal envelope. Fortunately, the fix was pretty cheap and simple to install. I'm anticipating warmer winter nights at home as the window by our bed should insulate better against the cold. Expanding polyurethane spray foam may not seem like a 'green' product at first, but it fills a need and a gap. Now, on to the next project!

More Info:

Air Seal and Insulate with ENERGY STAR

Weatherize Your Home ­ Caulk and Weather Strip

What's That Stuff - Polyurethane Foam

Insulated glazing / Double pane window