Not All Spray Foam Is the Same

One thing that's important to understand is that “foam insulation” doesn't describe one single product.

Open-cell spray foam typically provides an R-value in roughly the same range per inch as fiberglass insulation. Closed-cell foam is different and can provide approximately R-6 or more per inch. Fiberglass is generally around R-3 to R-4 per inch.

So simply saying that a house has spray foam doesn't tell you very much.

You need to know which product is being used, how much is being installed and what problem it is intended to solve.

The Attic Can Be a Different Story

One application I find particularly interesting is insulating along the roofline and bringing the attic into the home's thermal envelope.

In our climate, attics can become extremely hot.

If the HVAC equipment and ductwork are located in that attic, they are operating in a much harsher environment than the rooms below them.

Creating an unvented, insulated attic can dramatically reduce attic temperatures and reduce the heat gain affecting HVAC equipment and ductwork. Department of Energy research has found meaningful energy benefits from conditioned attics, particularly where mechanical equipment is located in the attic.

That's a very different benefit than simply saying, “Foam has a higher R-value.”

You're changing the building envelope.

What About Foaming the Walls?

This is where I think homeowners should slow down and look at the numbers.

If you're comparing open-cell spray foam with a properly installed fiberglass system in a standard framed wall, the nominal R-values can be fairly similar.

Spray foam can provide better air sealing because it expands into cracks and gaps, and that can have value. But that doesn't automatically mean the additional cost will produce enough energy savings to justify the investment in every house.

Closed-cell foam can provide substantially more R-value per inch, but it also comes at a higher cost.

Open-cell spray foam in the southeast typically costs between $1.20 and $1.80 per square foot installed, while closed- cell spray foam generally ranges from $1.80 to $2.50 per square foot installed.

So instead of asking whether foam is better, I think the homeowner should ask:

What benefit am I buying, and is that benefit worth the additional cost in this particular house?