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Q.I plan to install rigid foam insulation in a crawlspace. As far as I know, most types of rigid foam insulation can’t be left exposed but need to be covered with a layer of drywall for fire resistance. Is there a type of rigid foam insulation panel available that can be left exposed?

A.Corresponding editor Paul Fisette responds: Not that I know of. However, most building codes allow the installation of unprotected rigid foam in a crawlspace that has no open connection to a basement, as long as the foam has passed alternative testing procedures. Dow Styrofoam and Owens Corning Foamular are two products that pass the burn test and can be left unprotected in an isolated crawlspace.

Building codes restrict the use of unprotected foam in habitable or accessible spaces. Different code jurisdictions may have particular code sections that deal with this issue. Some codes say that if your crawlspace is connected to a basement, you need to cover the foam with an ignition barrier like 1/4-inch plywood or particleboard. Where inspectors draw the line often depends on whether there is a mechanical system in the crawlspace. The thinking here is that a fire could be set off by either the equipment or the activity of people in the space. When in doubt, it always pays to talk to your inspector during the design stage.