Energy Benchmarking Begins at Your Roof

By Bill McHugh, CRC Executive Director

Whether it’s a new project or a retrofit, saving energy and money starts at the top. Nowhere are a building’s extremes more evident than the roof, especially last winter season. This is where heat is lost in winter and infiltrates in summer; where wind and precipitation meet the building’s top with a vengeance, challenging it physically and structurally.

When looking at energy performance, why not start by looking at the roof? Why? The roof is a big deal when it comes to energy. And, the City of Chicago’s new Energy Benchmarking Ordinance means certain sized buildings will have to report energy usage which will be available, open and public.

To keep the building marketable, building owners and managers will try to find ways to decrease the building’s energy usage. Some energy saving ideas will be more effective at affecting energy usage than others.

Insulation can provide some payback, but can hit diminishing returns quickly. Rooftop gardens keep excess water out of the city’s wastewater treatment system, while photovoltaic solar panels generate electricity and reflective roofs provide lower rooftop temperatures in the summer. But, it all starts with a good roof, reasonably priced and maintained by professionals so that the investment lasts.

Insulated Roofs

One way to help an energy benchmarking activity for the building owner is by adding insulation to the roof assembly. An amount between about 2½ to 3 inches thick and an R-20, installed in multiple layers, will prevent air leakage and thermal shorts at board joints. Old roofs were lucky to have between R-8 and R-10. The R-20 complies with clarifications to the 2012 Illinois Energy Conservation Code.

Building owners and managers investing in more insulation to improve their City of Chicago Energy Benchmark performance should pay attention to the quality of the roof being installed over the insulation. That’s because gains in R-value with a new roof are lost if the insulation gets wet due to roof leaks.

Reflectivity

Scientists have been debating about rooftop color and energy savings in northern climates. A black roof gets very hot in the summer. A reflective roof, white, grey or even ballast, which can tame the soaring rooftop temperatures Chicago sees in the summer, might reduce some energy usage by cooling off things a bit. While the jury is still out, there are some who state that a medium to light color might help save spring and fall heating, while reducing summer temperatures.

Ballasted

Graveled roofing systems can be conventional and sustainable. The weight, or “mass,” along with energy saving insulation, brings value to the rooftop by approaching the performance of lighter colored, smooth surface roofs after aging a few years. The City of Chicago’s Urban Heat Island Ordinance allows the use of graveled roofs. It also allows for the use of ballast, as long as it is 17 pounds providing mass effect.

Solar Panels—Photovoltaic or Solar Thermal

New technologies exist to provide energy producing devices that are either part of the roofing membrane or separate devices used to generate electricity while absorbing the sun’s rays. Photovoltaic-based systems are the most efficient, commercially available solar panel technology on the market—so efficient that on many sunny days, a building owner may be able to sell excess power back to the grid, reducing energy bills. Solar thermal systems use color to heat water within the panels for energy. Regardless of the panel type, if the installer doesn’t know roofs, they can cause damage by allowing water to infiltrate into the insulation, eliminating the energy savings from the roof assembly.

Rooftop Gardens

While aesthetically pleasing to the community, rooftop gardens also provide excellent benefits to the building owner. The rooftop garden system needs to be installed right the first time, as unburying the roof can be costly to find and fix a leak, even with electric field vector mapping installed.

Most importantly, rooftop gardens can slow the drainage of water flowing into drains and overtaxing our combined sanitary and storm drainage system. By holding rainwater, we can keep Lake Michigan cleaner.

Whether it’s the ballasted roofs throughout the City of Chicago and suburbs, reflective roofs at Midway Airport, the rooftop gardens atop the Chicago Cultural Center and Chicago’s City Hall or the many photovoltaic panels on projects throughout the metropolitan area, the Chicagoland Roofing Contractor companies can install quickly and inexpensively because of a well-trained, consistent workforce and great management of the roofing process, at the best price. Visit www.chicagoroofing.org to find the best value in roofing contractor services.

Image: Mika Hirsimäki

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