Environment Matters

Building owners always are looking for ways to save money—and they do so even more during tough economic times. Roofing contractors know one way their customers can save money is to reduce a building's energy costs by increasing the amount of roof insulation. However, contractors often are unsure how to illustrate the potential savings to their customers.

To assist roofing contractors, in 2007, NRCA, the Polyisocyanurate Insulation Manufacturers Association and The Roofing Industry Alliance for Progress developed EnergyWise Roof Calculator Online. This online application offers an interactive, graphical method of constructing virtual roof assemblies to evaluate thermal efficiency and estimate energy costs.

EnergyWise Roof Calculator Online also provides minimum thermal requirements established by ASHRAE 90.1, "Energy Standard for New Buildings Except Low-Rise Residential Buildings."

In February, NRCA released an updated version of EnergyWise Roof Calculator Online.

The original

EnergyWise Roof Calculator Online's original version addressed only ASHRAE 90.1's 1999 edition, which contains 26 look-up tables with U-factor and R-value requirements based on a project city's climatic data (heating and cooling degree days).

ASHRAE 90.1-1999 also includes an exception that takes into account a roof surface's solar reflectance. A roof assembly's U-factor can be reduced by a multiplier if the roof surface has a minimum total solar reflectance of 0.70 and a minimum thermal emittance of 0.75. There are four multipliers, and the appropriate multiplier is determined by the number of annual heating degree days.

What's new

NRCA updated EnergyWise Roof Calculator Online to include information from ASHRAE 90.1's 2004 and 2007 editions.

NRCA's updated EnergyWise Roof Calculator Online

In ASHRAE 90.1-2004, the 26 look-up tables have been reduced to eight. And instead of using climatic data to determine which table to use, this determination now is made based on a project's climate zone. ASHRAE 90.1-2004 assigns each U.S. county a climate zone. The exception to the minimum thermal insulation requirements still remains; however, it is determined by climate zone instead of heating degree days. Furthermore, the exception is limited to Climate Zones 1 through 3.

In developing ASHRAE 90.1-2007, ASHRAE undertook a long-term strategic objective it intends to meet by 2010 to increase buildings' energy efficiency upwards of 30 percent more than what was recommended in previous standard editions.

For example, the minimum requirement for insulation entirely above a roof deck for residential and nonresidential buildings has been raised from an R-value of 15 to 20 for buildings in Climate Zones 2 through 8.

ASHRAE 90.1-2007 also contains several revisions to the exception for reducing the amount of thermal insulation. First, the exception is renamed to include high-albedo roofs. Second, this edition replaces the multipliers with a look-up table. Lastly, ASHRAE 90.1-2007 includes the option to meet a minimum solar reflectance index instead of meeting minimum reflectance and emittance values.

Additionally, a Web page has been added to EnergyWise Roof Calculator Online where users can select and access the version they need.

Check it out

NRCA encourages roof system designers to try the updated EnergyWise Roof Calculator Online. The calculator can be accessed for free at energywise.nrca.net.

Joan P. Crowe, AIA, is an NRCA director of technical services.