by Dave Evers, PE, and Rich Grabmeier RRC, LEED AP
The roof assembly is an important aspect in achieving energy code compliance because it often accounts for a large portion of the building envelope. It becomes even more critical in single-story non-residential projects such as manufacturing plants, warehouses, distribution centers, retail stores, and offices.
The most recent code updates include changes that can have significant impact on how roofing decisions are made. While the 2015 International Energy Conservation Code (IECC) is mostly unchanged from the 2012 edition (and will carry through to 2018), the requirements in American Society of Heating, Refrigeration, and Air-conditioning Engineers (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, have changed significantly with the 2013 edition. Today’s ASHRAE standards more closely align with the latest IECC, calling for much lower U-factors in all climate zones for both semi-heated and conditioned facilities. Additionally, the most recent version increased the U-factors assigned to many of the earlier prescriptive assemblies by 30 to 50 percent, so there are fewer prescriptive options that comply today than in previous years.
When making roofing decisions it is no longer about just meeting code, but rather meeting it in the most efficient way. Therefore, it is important to know the ins and outs of energy requirements and what options are available.
Codes, standards, and zones
IECC and ASHRAE 90.1 design standards are updated every three years, with new standards to be met. A thorough understanding of local code is imperative. Generally, builders on most projects will need to adhere to a particular edition of the IECC, which contains an alternative compliance option to use the ASHRAE standard (but one must adhere to the full code for the entire project). Some states have adopted their own codes or have made amendments to IECC. The particular standard year adopted by each state will also vary.
The Department of Energy (DOE) makes it easy to determine codes by state with its online map. Some states have not adopted an official code, so builders in this scenario need to work at the municipal level to determine which code and standards to follow on a given project.
Once the state code is determined, identifying climate zone is the next step. The eight climate zones in North America, listed within both the ASHRAE standard and IECC, are important because the performance requirements differ. Codes become more stringent as one travels north, into harsher winter climates. The type of roofing materials selected may need to meet a ‘cool roof’ standard, in addition to the insulating values. Cool roofing standards may require a certain verified maximum solar reflectance and emittance of a roofing product. This criteria varies by climate zone and roof pitch.
After dealing with code and climate zone, it is important to determine the energy demand for the building being constructed. Demand falls within three categories:
1. Low-energy buildings, as recognized by IECC and ASHRAE, have no air-conditioning, and a heating capacity of less than 19.3 watt/m2/C (3.4 Btu/hr/sf). For this type of building, no energy code compliance is required as the energy consumption is not deemed high enough.
2. Semi-heated buildings are not specifically covered in IECC, but the code allows a compliant option to use the ASHRAE 90.1 standard for the semi-heated end use. Semi-heated facilities are buildings having a heating capacity greater than 19.3 watt/m2/C, but less than the prescribed maximum heating capacities outlined for the various climate zones.
3. Fully conditioned buildings, recognized in both IECC and ASHRAE, includes any building with air-conditioning or a heating capacity greater than the semi-heated building category. The insulating values required for a semi-heated building are less than a fully conditioned building. This was deemed appropriate as the annual energy consumption is also typically lower than a fully conditioned and more highly insulated building.