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Improve Home Performance with Spray Foam Insulation

Published on: July 25, 2012

Most people are familiar with spray foam insulation as a material that can be used to fill awkward spaces: gaps around window and door frames, the space between the foundation wall and top plate, the spaces around lighting and mechanical openings, and the outsides of exposed HVAC system vents.

Spray foam is certainly a fine choice for those applications, and being able to seal and insulate odd-shaped and difficult to access surfaces can greatly improve building and HVAC system energy efficiency.

However, spray foam is being used for much more these days. The price of spray foam insulation has gone down, and modern formulations are safe and stable. It’s now practical to use spray foam for large projects, including wall and attic insulation retrofits. This article will focus on the use of spray foam for attic insulation.

The vented attic

For the past few decades, American builders have been constructing houses and other sloped-roof buildings with fully vented attics. This has been mandated by code, and there are good reasons for it.

Unvented attics are prone to moisture issues. During the winter, the warm, moist air from below makes its way into the attic through electrical and mechanical penetrations. Because the attic is insulated at the joist level, the underside of the roof is cold. When the interior air hits the roof, it condenses. Structural problems can develop due to moisture and rot. Adding ridge and soffit vents keeps the moist air from lingering.

In warm climates, the attic ventilation helps to keep the attic cooler than it would be otherwise.

The unvented attic

During the past ten years, builders have come up with a new strategy, and the building codes and local authorities now consider it an acceptable alternative approach: unvented attics.

In an unvented attic, the attic insulation is placed on the underside of the roof. Closed cell spray foam insulation is what makes this easy and effective. Spray foam can fill the cavities between the rafters or the truss top chords, and additional insulation can be added below the roof structure. Closed cell spray foam attic insulation doubles as an air barrier and vapor retarder, and condensation becomes less likely. When insulation is provided at the attic ceiling level rather than the floor, the attic becomes a conditioned space.

In warm climates, where ducts are often routed through attics, a conditioned attic will increase the efficiency of the HVAC system by keeping the ducts cool during the summer.

Your HVAC system is probably responsible for at least half of your total energy use, and the cost keeps going up and up. Upgrading your insulation can significantly reduce the need for heating and cooling. Insulating your unvented attic is an easy and economical way to do that. With spray foam insulation, it’s possible to create an insulated, unvented attic without risking moisture problems