Ask the Builder: The pros and cons of foam insulation

A new home is being built on my street. I’ve visited the job site countless times to check on the progress and to observe the quality of the workmanship. So far I’ve recorded nearly 40 videos showing mistakes and shortfalls. You can view the videos on my website. The link is at the end of this column.

Days ago, the insulation that was put in the wall cavities. It’s closed-cell foam.

Thirty-seven years ago, I was the first person in Cincinnati to install foam insulation in a residential large room addition project. The homeowner was in the poultry business, supplying succulent chickens to the best restaurants and butcher shops in greater Cincinnati. He had deep experience with foam insulation because it was used to insulate all his refrigeration equipment and cold rooms at the factory.

This forward-thinking customer insisted on foam insulation. Who was I to challenge him? It turned out excellent. The foam sealed all air leaks that normal fiberglass insulation methods could not.

Air infiltration is a silent energy thief. Even my own current home suffers from this wretched disease. (It’s important for you to realize I didn’t build the home I currently occupy.)

The walls of my customer’s room addition were all 2x6s, and he insisted the foam be sprayed to fill the entire cavity. Once the foam hardened, it was shaved smooth to the face of the studs. These fully-filled foam walls also helped make the walls stiff. There was no way the walls would rack out of square with the rigid foam in between the studs. Decades later, our industry would see similar wall characteristics once structural insulated wall panels (SIPs) became mainstream. SIPs were invented, believe it or not, in the 1930s by the Forest Products Laboratory.

The most important thing to consider when comparing any insulation material against another is the R-factor per inch. Most closed-cell foams have an R-factor of 6 or 6.5 per inch of thickness. The pink fiberglass that might be in your walls is between 2 and 3 R-factor per inch. If you put in the same R-factor in a wall no matter the material, the thermal performance will be the same; all insulation does is slow the movement of heat. Heat travels to cold. Never forget these things as you evaluate what insulation to use.

What are the negative aspects of foam insulation? I visited the Spray Polyurethane Foam Alliance (SPFA) website. On their FAQ page you’ll find great information. The SPFA readily admits that foams emit chemical compounds and odors into the air. Some studies show that the release of volatile organic compounds are minimal after the foam has cured. Yet, as we all should know by now, different studies can produce widely varying results. If you’re chemically sensitive, you best be very careful.

The next biggest negative in my opinion is the cost. Keep in mind that trying to calculate a return on investment (ROI) is harder than trying to roll a boulder up Mt. Washington. It’s a complex multivariable problem. But using a small amount of common sense, you can determine if you’ll ever break even using foam insulation over the baseline fiberglass batts.

I decided to price out the insulation cost of the house that’s being built just down the street from me. The house has two stories with a total of 2,560 square feet of living area. It’s got 2,482 square feet of wall area that requires insulation.

Keep in mind these prices are from January 2023, and the annual inflation rate at this time is north of 5%. The current price to install traditional fiberglass batts and a plastic vapor barrier is $3,917. The price for closed-cell foam that’s the exact same R-value as the fiberglass is $12,410. The price for a hybrid system of foam plus fiberglass to fill the 2x6 wall cavity is $9,679.

All three systems would have the same R-value and heat loss or heat gain. The only difference is any heat loss attributed to air infiltration. Air infiltration can vary wildly but modern construction methods where a tape is applied over the seams of the exterior sheathing as well as around all windows and doors keeps it to a minimum.

Let’s assume you pay $4,000 a year to heat your home and that air infiltration with a fiberglass system costs you an extra 5%. At $200 per year, it would only take my new neighbors 40 years to break even using spray foam in their house! It really pays to think these decisions through!

Here’s the URL for the video playlist: https://www.askthebuilder.com/new-house-build-video-playlist/

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