How to Boost Internal Wall Insulation With Slow-Rise Spray Foam

Do you want your house to be cooler in summer, warmer in winter and less expensive to heat and cool? There’s an under-used insulation upgrade technique you should know about. I got to see it in action a few years It’s one of the best ways to improve the energy performance of millions of homes plagued with insufficient insulation in hollow wood frame walls.

The job happened in a home in Petrolia, Ontario, and it involved a do-it-yourself spray foam injection kit.  Slow-rise spray foam is not mainstream, but you can find it from several suppliers. It offers one of the few options for hollow wall upgrades. The process is simple but surprisingly effective. I know because I monitored the results as they were happening during the installation you can see on the video above.

Millions of older homes were built in cold climates, with wood frame walls that never got filled with insulation because energy was so cheap at the time.  Fast-forward 70 or 80 years and the world of energy economics is entirely different. The modern home I worked on didn’t have insulation in the garage walls, and that’s what we were fixing. Even a few hours after the job, you could feel the garage space heating up, even though it was cold outside.

Isn’t Spray Foam Dangerous?

Over the years mainstream media has aired stories about the dangers of spray foam, but none of the information I’ve seen offers anything new. Yes, spray foam needs to be applied correctly, while wearing safety equipment, but that’s easy to do.  The dangers, small as they are, happen only during and shortly after application. Contrary to sensationalist impressions,  spray foam is safe and effective when used correctly. I’ve used it in my own projects and my own home with no concerns. Polyurethane spray foam, the broad category I’m telling you about here, has been around for 50 years, and it remains code approved everywhere that I know of.

Seeing the Invisible

Installation of this stuff is pretty cool to see. Drill holes every so often in the wall (either interior or exterior surfaces), insert the nozzle of a slow rise spray foam kit, then fill the space. The foam climbs as it expands, then hardens. You go from a hollow wall with hardly any insulation to a very well insulated wall that meets 21st century standards.

Since the foam gives off a little heat as it cures, it’s possible to use an infrared heat gun to “see” that foam is getting to all nooks and crannies inside a wall. The light areas of the infrared image above shows wall cavities partly filled, with the foam installer standing to one side, giving off plenty of heat himself. That’s what you can see to the right. The lighter areas are warmer, and show up on the infrared camera I took to the job. Besides looking interesting, the pattern of light and darker areas alerts you to any places inside the wall the were missed. If there are any, just bore more holes in the wall and inject foam where wires or nails or wood blocking may have prevented the foam from flowing and expanding where it should have gone the first time.

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– Steve Maxwell