Building Code R-Values and ASHRAE for Commercial Roof Applications

July 27th, 2012

Building codes continue to evolve, however their intended purpose remains the same.  Provide a means to safeguard life and protect the public welfare through regulating the design, construction practices, construction material quality (including fire performance), location, occupancy, and maintenance of buildings and structures.

The code has multiple compliance paths – from the simple, prescriptive compliance approach (checklist) to complex building energy simulations (performance-based compliance). When the prescriptive levels change (efficiency levels are increased) a new bar is also established for those seeking to use the more complicated energy simulation tools. The changes are climate zone and building type specific.

R-value, a measure of the resistance to heat flow, continues to play a very important part in establishing the energy performance requirements.  As heating and cooling continues to be one of the nation’s largest ongoing expenses in owning and operating a commercial structure, specifications for R-values continue to be evaluated and updated to comply with the newest construction standards.

The ASHRAE 90.1 Standard addresses building envelope and system requirements for commercial buildings, residential buildings higher than three stories, and semi-conditioned buildings (warehouses, etc.). It is the nation’s model standard for establishing the energy performance requirements of these building types.

ASHRAE (American Society of Heating Refrigerating and Air Conditioning Engineers) has set the pace over the last two decades by issuing standards for developing energy efficient buildings. These standards are adopted by state and local municipalities then incorporated into active building codes. Historically, these updates in standards have resulted in industry trends.  One trend worth noting is polyiso insulation. It continues to be one of the Nation’s most widely used and cost-effective insulation products and has been cited by the U.S. Environmental Protection Agency for its responsible impact on the environment.

Currently there are three ASHRAE Standards commonly observed to achieve building envelope energy efficiency and performance. Polyisocyanuate insulation is a key and active component in achieving these standards for commercial roof design.

ASHRAE  90.1-2004 is the standard many states still recognize and use which has been the energy code referenced in the International Building Code (IBC) and the International Energy Conservation Code (IECC).

ASHRAE 90.1-2007 made a significant change in the minimum recommended / required values for roof and wall insulation levels. Standard 90.1 - 2007 increased the above-deck roof insulation requirements from R-15 to R-20 mandating a 33% increase to nearly every U.S. climate zone.

The International Energy Conservation Code (IECC), which is rapidly being adopted by state and local code development throughout North America, incorporates the ASHRAE 90.1-2007 into its standard. However the next standard of code compliance which is being proposed by ASHRAE will likely displace the 2004 and 2007 standards over time, as the North American Standard.

ASHRAE 90.1-2010 is currently being developed with increased requirements for commercial roof applications. The new standards are expected to range from R-20 in the southeastern U.S. to R-35 in the far north. Since goals for energy conservation are becoming more aggressive, so will the standards for energy performance in commercial buildings.

As a result of these continuously evolving ASHRAE standards, the use of polyiso as a commercial roofing insulation sees an increased demand. The material’s ability to help building owners, designers, engineers and contractors meet and exceed energy efficiency demands will continue to create opportunities for polyisocyanurate into the foreseeable future.

Information about all three ASHRAE Standards, polyiso roof insulation and other resources about efficient building envelopes can be located at