Big changes in energy code requirements occurred with the 2009 and 2012 International Energy Conservation Code® (IECC) and the ASHRAE Standard 90.1-2013 that followed.
The newest versions of IECC and ASHRAE Standard 90.1 call for one to four inches of exterior continuous insulation depending on the building location by climate zone, even in warmer zones where foam board insulation had not previously been required.
Here’s what these requirements mean for cold-formed steel (CFS) assembly design and field integrations.
CFS framing assembly design
Architects, engineers, and contractors need to understand how to apply foam board insulation products as well as address the installation of cladding through the insulation, extensions for window and door openings, and other installations related to wall assemblies containing exterior insulation. Here’s what to do:
Don’t be quick to change
While the national model energy codes require greater thicknesses of continuous insulation (e.g. solid foam insulation), it may be tempting to choose a framing system that requires less continuous insulation than a CFS system.
But why give up the strength, durability, and other benefits of CFS framing when a variety of CFS wall assemblies meet IECC and ASHRAE 90.1 requirements?
Designers have a range of options. CFS walls vary in terms of claddings, the number of CFS members used in the framing, the thickness of CFS members, and other characteristics. And, a variety of methods to determine a wall assembly’s thermal performance — including new modeling software — exist and are approved for use.
According to the Steel Framing Industry Association (SFIA), many architects and large corporations (e.g. Target, Walmart, etc.) are moving toward conducting building simulations to comply with the energy code. This approach, known as the simulated compliance or performance path, allows trade-offs of one component of the energy system for other parts.
Understand how to calculate thermal performance
In general, energy codes and standards call for three ways to determine a wall assembly’s thermal properties:
- Prescriptive R-value. When a code specifies a prescriptive R-value, you compare the R-values of the wall cavity insulation and the exterior continuous insulation. The wall insulation R-value total must be equal to or greater than the R-values listed in the code.
- Prescriptive U-factor. Some energy codes specify a U-factor for the entire wall assembly, rather than an R-value just for the insulation. In this case, the designer could check published tables of U-factors for common CFS wall assemblies with a variety of combinations of insulation. The Steel Framing Alliance guide, “Thermal Design and Code Compliance for Cold-Formed Steel Walls, 2015 Edition,” includes U-factor tables for a variety of CFS wall assemblies.
- Performance pathways. IECC and ASHRAE 90.1 include performance pathways that require building simulations. These new pathways include the total building performance option, energy cost budget method, and the Standard 90.1 Appendix G performance rating method. COMcheck software from the U.S. Department of Energy can help determine if a design meets the IECC and ASHRAE 90.1 requirements.
Energy code compliance will generally require adjustments in how CFS assemblies are installed. This could include the application of energy efficient framing methods such as a two-stud corner versus a three-stud corner, different framing methods for window and door openings, and the framing factor (e.g., 24 inches on center framing versus 19.2 or 16 inches on center).
Attaching continuous insulation materials
Attaching foam board insulation to an exterior brings the surface of those materials further from the face of the framing. The fasteners used will have to resist greater bending forces, since they must cantilever farther to support the exterior cladding, and the soft nonstructural continuous insulation provides little to no support of the fastener or cladding.
The SFIA paper, “Impact of Energy Code Changes,” indicates that this is a critical design issue with heavy cladding materials on multi-story buildings that could threaten occupants or visitors walking below if not designed and installed properly.
Attaching exterior items
Whereas windows, doors, and light fixtures would normally attach to CFS framing, attachment points may not be directly accessible with foam insulation in place.
Therefore, pay extra attention to certain issues: the corners when attaching cladding, jamb extensions for exterior doors, supplemental framing to attach window flanges, and possible changes to the fastening system.
Adjusting the interior space
The requirements to add foam board insulation to CFS and wood-framed assemblies can reduce a building’s interior square footage. The exterior walls may be thicker than other types of framing systems. If there’s no room to expand the envelope footprint, then any added wall depth will have to come from the interior space.
What do the new energy code requirements mean for CFS assembly design and field integrations? They mean doing some thermal calculations and modifying some installation procedures. Of course, what you decide to do in the end depends on your specific state or jurisdiction’s energy code requirements.
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