Vinyl is the most popular siding material in the U.S. But when it comes to adding heating or cooling resistance (R-value), the material is, well, hollow.

Welcome, then, to foam-backed siding, in which the foam is either applied at the factory or in the field. Combining foam insulation and siding in a single product gives vinyl siding solidity, provides a vapor barrier and an energy-saving capability of around R-4, according to manufacturers.

“Normally, siding is a design element,” says Dave Cook, owner of Feldco, a Chicago-area window and siding company that has offered foam-backed siding for two years. “The fact that we can add the energy-saving component to that makes this a two-for.”

HOW IT WORKS

Just how does foam-backed siding keep a home warmer? Bear in mind that a new 2x4 batt in a stud wall offers an R-value of somewhere around R-13; older and poorly detailed batts or spray-in material compressed in the stud bay offer less. And studs themselves have low R-value. Because foam-backed panels interlock in a contiguous sheet over the entire sidewall, they enhance resistance to thermal bridging and improve thermal performance.

The systems work for heating and cooling climates. And water vapor can pass through without turning into liquid water. However, liquid water — whether from heat transference vapor or from precipitation — will get behind the siding. Every manufacturer's product is designed to help keep an intact drainage plane for liquid water to escape and to deal with water vapor. (Note: You must properly detail all penetrations in order for water to escape.)

OTHER ADVANTAGES

The foam is applied either at the factory, or in the field.

The foam is applied either at the factory, or in the field.

From the installer's perspective, foam-backed vinyl siding is easy to work with because it's not as floppy as vinyl and it hangs straighter on the building. Deeper channels on J's, corners, and accessories are required, the exact depth depending on the profile.

Mike Hazelwood, of Minnesota Rusco in Hopkins, Minn., says that his company, which has offered field-applied foam-backed siding as its premier product for three years now, emphasizes all those elements — durability, impact-resistance, energy-savings, permeability — when presenting in the home. “It's a combination of everything,” Hazelwood says. “The ability to insulate, drain, and resist bugs from bedding inside it. It's a good pitch, compared with flat installation.

“Foam-backed siding does cost a bit more …” — Hazelwood estimates 15% more — “… and is more of a job to install, so the truck-and-ladder guys don't use it.” —Mark Clement is a freelance writer and former contractor based in Ambler, Pa.