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7.1 Roofs and Attics

This part of the Energy Efficiency Manual presents energy conservation measures that minimize heating and cooling by effective insulation of roofs and attics. Roofs or attics make up a large fraction of the total surface area of most buildings, making it especially important to insulate them well. Roof heat loss is especially severe during cold weather because the roof faces the night sky, allowing maximum radiation loss. The roof is exposed to precipitation and wind, which carry away any heat that makes its way to the outer surface. And, the interior temperature is highest inside the roof or attic, which drives heat outward.

By the same token, roof insulation is especially important for reducing solar heat gain during warm weather. Roofs have especially high solar gain because of their orientation and because roofing surfaces tend absorb solar heat strongly.

Roofs and attics have large, unbroken surfaces that offer relatively easy access for installing insulation. Therefore, they often provide the most economical opportunity for reducing heat loss and heat gain. In new construction, good roof insulation adds little to overall cost. In existing buildings, improving roof insulation may be your only opportunity for improving the building’s insulation on a large scale. You can usually find a way to improve roof or attic insulation without having to disrupt other building components.

The various methods that you can use to insulate roofs are explained here, with emphasis on the important advantages and drawbacks of each method. The methods include insulation above the roof deck, below the roof deck, and insulated suspended ceilings. You will learn to select the best insulation materials for each method, including glass fiber batt insulation, rigid foam board insulation, poured insulation, and other materials. Important insulations properties, such as R-value, fire ratings, moisture resistance, and other essential characteristics are explained. Equally important, you will learn about vapor barriers and their relationship to insulation.