Is spray-foam insulation a health hazard?

A few weeks ago I wrote here that spray-foam insulation was worth considering for an old house undergoing an energy retrofit. Although it's expensive, it has two big advantages over many other types of insulation--high R-values and the ability to seal air leaks.

If there is a potential drawback it's that urethane foam sticks like glue. It would be very difficult to remove if ever that became necessary, and in an historic home this lack of reversibility might be a problem.

It turns out there's more to it than that.

I later came across a blog at Green Building Advisor (www.greenbuildingadvisor.com), a website devoted to sustainable building practices and building science (full disclosure: I also write for this site). A number of building experts and homeowners weighed in on spray-foam insulation, and the conversation was interesting to say the least.

A potential for lingering odor

When urethane foam is applied, two chemical components are mixed in the nozzle of a high-pressure gun. After it has cured, the foam should be an inert material that neither has an unpleasant odor nor poses health risks to the occupants of the house.

But in some cases this may not be what happens.

Several people wrote to say that a strong odor hung in the air long after the foam should have cured. Some of them reported health problems, including one woman who said her brother was considering selling his house after open-cell foam had been applied.

In short, said a member of the Environmental Protection Agency's (EPA) work group on spray foam, we need to know more about urethane foam insulation. Is there a chance that cured foam has the potential to off-gass chemicals that make people sick?

Installation may be the wild card

When you buy a sheet of rigid foam insulation you get a finished product, made in a factory under controlled conditions.

That's not the case with spray-foam insulation. It's mixed on site, and it can be affected by a variety of things, including the skill of the applicator, the equipment, even temperature and humidity.

How the foam is applied also affects its properties. Spray it on too thickly and it may not develop the density it's supposed to have. Or, it might smell.

The bottom line is that the cured foam may not have exactly the properties the manufacturer intended.

Consider your options

None of this is to say spray-foam should automatically be avoided. It's been applied successfully in large numbers of houses whose owners haven't suffered any ill effects. And it's highly effective.

Our roof is insulated with closed-cell urethane foam. Long after the foam was applied, there was a lingering odor in a crawlspace under the eaves. But no one ever had a health problem and I'd choose foam again.

But it does suggest that being a savvy consumer is a good idea.

Dense pack cellulose and spray-in alternatives such as Air Krete, made with magnesium oxide, are worth considering if there's someone in the family with chemical sensitivity, or if the risks of urethane foam simply seem too high.