By Maciek Rupar
From the January/February 2015 issue
The International Energy Conservation Code, 2012 Edition (IECC 2012) introduced a number of building energy performance requirements that make compliance challenging for commercial reroofing projects in jurisdictions that have adopted the code. As of January 1, 2015, 14 states (California, Delaware, Idaho, Illinois, Iowa, Maryland, Massachusetts, Montana, Oregon, New York, North Carolina, Rhode Island, Utah, and Washington) and the District of Columbia have adopted energy codes based on IECC 2012. Meanwhile, some local jurisdictions in other states also adopted similar energy codes.
Introduced in 1998 by the International Code Council (ICC), IECC addresses energy efficiency. The U.S. Department of Energy has determined that IECC 2012 requirements represent a 30% improvement in building energy efficiency over IECC 2006. This improvement is achieved in substantial measure through increases to minimum building envelope requirements, including roof assemblies.
Facility professionals considering reroofing should be aware of the new requirements because these may materially affect a project’s scope of work, material selection, and methods of installation. They also should examine return on investment projections for energy code mandated upgrades to the building envelope.
Low-slope roof system replacements can be particularly challenging because the IECC 2012 prescriptive provisions for the building envelope are intended for new construction and do not offer specific relief for conditions unique to reroofing. Complying with IECC 2012 is further complicated because of different code interpretations by building officials and nonuniform enforcement.
Minimum Roof Insulation R-value
Roof system designers commonly specify roof insulation thickness to comply with energy code prescriptive requirements. For commercial buildings, IECC 2012 generally requires higher minimum levels of roof insulation than previous editions.
The table at right highlights IECC 2012 prescriptive requirements for roof insulation. Additionally, the code requires skylight curbs to be insulated or rated for thermal performance in accordance with a specific standard.
The increased prescriptive requirements of IECC 2012 may cause additional design modification in common reroofing scenarios because of increased insulation thickness. For instance, when replacing a roof system with insulation installed above the deck, to accommodate an insulation thickness increase of 1″-2″ may require raising rooftop equipment, pipe penetrations, and parapets to maintain appropriate flashing heights. Roof drains or scuppers may also need to be raised. And where through-wall flashings and window or doorsills connect with the roof system, they may need to be raised or relocated.
Facility professionals may be surprised by payback periods for roof assembly R-value increases. The National Roofing Contractors Association (NRCA) conducted an analysis of construction cost increases and corresponding theoretical energy savings for increasing by R-5 the thermal resistance of a hypothetical roof assembly on a single story, 10,000 square foot building. Payback lengths were determined for 16 U.S. cities representative of the energy code’s eight climate zones (see IECC Climate Zone map below). Local climate conditions and heating and cooling energy costs were considered. Increases from R-10 to R-15 had the relatively shortest paybacks ranging from 3.7 to 12.1 years, depending on location. Increases from R-20 to R-25 had paybacks from 12.4 to 61.3 years, while increases from R-25 to R-30 estimated paybacks from 27 to 133 years.
In commercial reroofing scenarios, relief from the additional insulation requirements may be available if existing insulation is not damaged and left in place, or by designing to comply with ASHRAE 90.1-2010, Energy Standard for Buildings Except Low-Rise Residential Buildings, which specifies lower minimum prescriptive R-values for some roof assemblies. Designing to meet ASHRAE 90.1-2010 is an alternative compliance path in IECC 2012 for commercial buildings.
Continuous Air Barrier
IECC 2012 Section 402.4—Air Leakage (mandatory) requires all commercial buildings, except those in the IECC map’s Climate Zones 1, 2, and 3, to include an air barrier that is continuous across all assemblies comprising the building thermal envelope. The air barrier may be located anywhere within the envelope provided it is sealed across all joints and transitions and around penetrations; installed to withstand design wind, stack, and mechanical ventilation pressures; and characterized as “deemed-to-comply” or through testing to not exceed a specified maximum air leakage rate. Compliance with the maximum air leakage rate requirement can be demonstrated for air barrier materials or air barrier assemblies or by testing the completed building. The code terms certain specific air barrier materials and assemblies as “deemed-to-comply.” Where these materials and assemblies are installed as air barriers in accordance with manufacturer instructions and other Section 402.4 requirements, they are considered compliant without testing.
Built-up roof membranes, polymer-modified bituminous roof membranes, and fully adhered single-ply roof membranes are deemed-to-comply materials and may be designated as part of the building air barrier by designers. Other roof membranes require testing or another deemed-to-comply air barrier to be installed elsewhere at the roof assembly (e.g., below the roof deck) to demonstrate compliance. In other words, additional costs have to be incurred to comply. For instance, where air leakage requirements are not addressed using either approach, a mechanically attached single-ply roof membrane or ballasted roof membrane do not comply with IECC 2012.
Further complicating air leakage compliance for roof systems is the classification of the deemed-to-comply roof membranes as materials (they are clearly assemblies of different materials constructed in place) and referencing air leakage test methods designed for testing wall assemblies and fenestration. Except when demonstrating compliance using a whole building air leakage test result, it is unclear what is to be tested and how. And these are just the considerations for new construction projects.
IECC 2012 applies the same air leakage requirements to reroofing. That this approach may be critically flawed quickly becomes clear. The design of a typical reroofing project does not specifically include air sealing details; the scope of work does not include detailing work to seal the roof air barrier to wall air barriers (many existing buildings do not have air barriers). Also, NRCA is not aware of any membrane roof system manufacturers who provide instructions for installation of their systems as air barriers.
In short, demonstrating compliance with IECC 2012’s air leakage requirements may be problematic for a typical reroofing project using a roof system not deemed to comply.
Solar Reflectance And Thermal Emittance
For roofs installed with a slope of less than 2:12 over air conditioned spaces located in Climate Zones 1, 2, and 3, IECC 2012 provides solar reflectance and thermal emittance requirements in Table C402.2.1.1. Compliance for roof covering materials may be demonstrated using initial or three year aged solar reflectance and thermal emittance ratings, or corresponding Solar Reflectance Index (SRI) values, reported by the ENERGY STAR roof products program and Cool Roof Rating Council (CRRC) Rated Products Directory. In practice, only white or very light colored surfaces comply with reflectance requirements.
The same section in the code provides a list of specific exceptions, which include roofs with photovoltaic and solar thermal systems, roof gardens and vegetated roof systems, some ballasted roof systems, above-roof decks and walkways, and rooftop HVAC systems.
Facility professionals should note the code requirements are for rated reflective and emissive performance and do not address actual performance.
Research conducted by NRCA indicates aged reflectances for roof covering surfaces exposed in-service at slopes commonly used in low-slope roof construction were lower than the three-year aged reflectance ratings available from ENERGY STAR and CRRC for equivalent materials. Conclusions from this research provide useful lessons:
- Reflective roof coverings in low-slope applications should be expected to experience higher in-service temperatures than would be expected with the currently reported three year aged reflectance ratings.
- Currently reported three year aged reflectance ratings should not be relied on to make decisions about rooftop temperatures and sizing of building mechanical equipment.
Daylighting is using natural light within a building to conserve electric energy. Often, skylights are used as part of a system. To be considered a daylighting system, a control system is used to sense ambient lighting within a space and reduce or turn off powered lighting when a desired level of natural light is available.
IECC 2012 Section C402.3.2 provides mandatory requirements for minimum skylight area and integration into a control system to provide daylighting in certain commercial building spaces in Climate Zones 1 through 5. Also, when specifying skylights, the code provides minimum performance requirements. Decision makers need to be aware that roof system replacements may trigger these requirements.
Code interpretations can be inconsistent and enforcement nonuniform for different jurisdictions enforcing the same code. NRCA expects IECC 2012’s application to be particularly challenging because many of its provisions are new and unfamiliar to building officials. In particular, application of the new provisions to existing buildings represents uncharted territory.
Rupar is director of technical services for the National Roofing Contractors Association (NRCA). In his role, he is responsible for responding to requests for technical assistance, maintaining and developing technical documents, and performing staff liaison duties for several NRCA technical committees. He holds a Bachelor of Science degree in materials science and engineering from the University of Illinois in Urbana-Champaign.