Insulation Design for Roofs: A System Perspective

As we move toward more energy-efficient buildings, there is a need for more accurate determination of R-value of the building. The design community is using integrated design and is looking at buildings as whole units, not as a collection of individual components. Building design is definitely moving to the “system” approach. For example, proper sizing of a building’s mechanical systems is based largely on the thermal resistance of the building envelope. Because of this more holistic approach to building design, and because the roof often plays a large part in the energy efficiency of a building, the roof should have its thermal resistance determined accurately.

As shown in this article, the “field of the roof R-value” is not the R-value of the roof as a system. Roofs have skylights, roof hatches, drains, vent stacks and mechanical units. Additionally, roofs are installed in a number of ways — adhered, mechanically attached, and loose-laid and ballasted. The components, accessories and installation method should be considered; the roof should be looked at in its entirety, as a landscape, when determining the R-value. And tapered insulation adds a level of complexity to the equation.