Roofing Trends: Roofs and Energy

As we head into the next decade, the biggest trends in the roofing industry—which are inherently connected to the direction of the entire construction industry—are related to energy efficiency and sustainability. This push towards energy efficiency begins with a well-insulated facility.

Over the past decade, higher and higher levels of insulation have been mandated with each subsequent edition of building and energy codes. The result is an increased thickness of overall roof insulation, which certainly is beneficial to a building’s energy efficiency.

Testing One, Two, Three
Roof systems are required by building codes to have minimum fire and wind resistance appropriate for the building type and location. Testing agencies, like Underwriters Laboratories and FM Approvals, perform fire and wind resistance tests and classify roof systems.

So how does this impact the energy efficiency trend? In order to achieve the maximum insulating benefit from roof systems, it is best to use at least two layers of insulation and stagger the board joints. This approach provides a more stable substrate for the roof membrane and minimizes the likelihood of unwanted air movement within a roof system.

A single layer of roof insulation means there is a high possibility of air movement from the deck to the underside of the membrane. And because air movement accounts for a significant portion of a building’s heat loss; staggered board joints are quite beneficial to the overall R-value of a roof system.

Proper design and installation of a roof system’s insulation layer are critical to the accuracy of the energy modeling of a building. If you assume a roof system has a design R-value of 30 but the insulation board joints align vertically and mechanical fasteners are used to secure the entire thickness of insulation, this could present a problem.

Studies have shown that this configuration can create a loss of R-value of over 15%. In fact, the in place R-value would be closer to R-25.

Reflected Energy
White and light colored, highly reflective roof surfaces also are trending up and have been for some time, mostly in the form of TPO and PVC single-ply systems. However, there are also reflective BUR cap sheets that provide similar reflectance. The benefit of roof surface reflectivity should be looked at from two perspectives: the specific building’s energy savings and the overall environment by reducing the ‘urban heat island’ effect.

Low rise buildings with large roof areas (relative to the entire building envelope) are likely to be more energy efficient during periods of air conditioning operation when a highly reflective roof surface is used to reduce solar gain into the building. On the other hand, a highly reflective roof will reflect the sun’s heat energy, subsequently reducing rooftop temperatures. This is overall beneficial for the environment regardless of building size, proportions, and location. Understanding the different perspectives about the benefits of using a reflective roof surface is important when determining if a building will or will not glean reduced energy consumption.