There are some wonderful things about spray foam insulation, but the price in health and embodied carbon is just too high.
A well-known website for home handypeople recently ran a post titled "Here’s Why You Should Use Spray Foam over Fiberglass." Even though it was far more expensive, they noted that it performs much better. "Spray foam can stop cold air from passing through your house, while fiberglass can have air leakage that will contribute to hotter or cooler temperatures in your home based on the weather."
I will confess that I used to love spray foam, and even have some of it in my own home where I had a tight ceiling space. If I were doing it over, I would not have it in my house. Here’s why:Spray foam does not necessarily stop cold air so much better than fiberglass.
It can shrink and pull away from framing. Allison Bailes of Energy Vanguard notes:
I've seen this only once, and it was with closed cell foam, but I've heard of it happening with open cell foam, too. I don't know the details, but I've heard it could result from a bad batch of chemicals, improper mixing, or too high a temperature. Whatever the cause, it's not a good thing.
Spray foam should not be installed by home handypeople but should be left to professionals.
It cures with an exothermic reaction that generates a lot of heat, and if you put it on too thick, it can cause fires.
Spray foam is a toxic fire hazard after it is installed.
One insurance guy called it “solid gasoline.” When it burns, it puts out very toxic chemicals including dioxins.
Spray foam is full of dangerous flame retardants.
Because it is so flammable, they can leach out and are endocrine disruptors. In her report, Margaret Badore noted that, "According to the Centers for Disease Control, "flame retardants, such as halogenated compounds, are persistent bio accumulative and toxic chemicals."
Spray foam is made from a long list of unhealthy chemicals.
A recent study put it at the bottom of the list of insulations rated according to health hazard. (Fiberglass was actually near the top!) Some people develop chemical sensitivities to it and are constantly sick when in a home insulated with spray foam. Robert Riversong has written:
In far too many instances, the home-owners have had to permanently vacate their new or newly-renovated homes because of chemical sensitivity apparently initiated by the insulation. As we know from other chemical sensitizers, such as formaldehyde, initial exposure causes increased and sometimes debilitating reactions to a wide variety of chemical substances.
Spray foam has a huge amount of embodied carbon because it is made from fossil fuels.
Chris Magwood has calculated that insulating a home with spray foam puts more CO2 into the atmosphere than it saves over the life of the home.
Spray foam is just as susceptible to bad installations as fiberglass or any other insulation.
Alison Bailes describes installations where spots have been missed, where it was not thick enough, where it was just botched. He concludes: "Don't assume that just because a home is insulated with spray foam that it's automatically a winner. Every product has its pitfalls, and spray foam is no exception."
There are some wonderful features about spray foam, most notably its high R value per inch and its ability to act as a continuous air barrier when properly installed. But I have come to conclude that the price, in terms of health and embodied carbon, is just too high. And, there are many greener insulations out there.