One of the major challenges with advancing energy codes is helping the homebuilding community learn how to comply with the latest energy codes because they are used to and comfortable with current construction standards and best practices. For instance, let’s take a look at the latest code’s insulation requirement. Ever-increasing levels of insulation required by each iteration of the energy code in framed walls has caused significant push-back from builders because they cause higher installation costs. This is due to the code’s prohibition against using traditional insulation construction methods. Builders wanting to use single-plane air and weather barriers are relegated by the code to using thicker, more expensive 2-by wall assemblies. Even builders who embrace the code-required exterior insulation must account for an additional 1”- 3” of exterior extensions around windows and doors to provide a structural nailing surface for mounting flanges. These extensions, called bucks, interrupt the single plane of construction that air and weather-resistive barriers are usually built on, requiring specialized installation techniques that add costs for training and alternative flashing, sealing, and framing materials and details.
What if there was a way to adhere to the new energy code and also satisfy builder concerns? Designs that blend traditional construction techniques with higher-performing assemblies are available that will do just that. Two of these assemblies are presented below for consideration.
One design is called Extended Plate and Beam Wall Construction, which uses, in part, construction methods builders are familiar with, and saves them money. Builders construct a typical 2×4 framed wall but replace the top plate and sill plate with 2×6 studs and 2×8 top and sill plates can be used with 2×6 studs for increased performance if needed. The extended plates create space to install 2” of rigid insulation board, and the face of these plates can be used to nail OSB or plywood to the wall, covering the rigid insulation and providing an exterior structural sheet for window and door nailing flanges. Fixing the exterior OSB/plywood to the top and sill plates also provides reinforcement to the wall to resist wind loads, another concern with exterior continuous insulation. The exterior structural sheathing creates a single plane to install the weather-resistive barrier, flashing and air sealing using common, familiar practices most builders already know. To be clear, this method of insulating does not qualify as continuous insulation, since the top and sill plates create thermal bridges. Therefore, compliance with the energy code would be achieved through the U-factor analysis pathway. If using REScheck or COMcheck, the assembly would be a custom entry. Details on this wall assembly can be found here: https://www.energy.gov/eere/buildings/articles/building-america-new-homes-case-study-advanced-extended-plate-and-beam-wall
Image source: https://www.energy.gov/eere/buildings/articles/building-america-new-homes-case-study-advanced-extended-plate-and-beam-wall
Another alternative to using exterior continuous insulation is called the “Mooney Wall” design, or the Furred “Continuous” Insulation Wall Assembly. Note that while “continuous” is in the name of this assembly, the insulation installed does not meet the definition of continuous insulation in the energy code and cannot be entered in COMcheck or REScheck as continuous insulation. The assembly involves building a standard 2×4 or 2×6 wall insulated with R-20 cavity insulation, then installing 1.5” horizontal furring strips across the interior of the wall to minimize thermal bridging through the wall framing members and increase the insulation installed by about R-6. The cross-furred assembly minimizes thermal bridges, significantly improving the performance of framed walls such that the Mooney Wall design complies with the U-factor requirements in the 2021 IECC. As the additional furring strips are added to the interior of the wall, traditional, familiar construction details can be used for mounting exterior sheathing and flanged window and door assemblies. The exterior of the wall can be finished the same way traditional walls were finished, with structural sheathing and a single plane for the weather-resistive barrier, flashing and air sealing. Furring on the interior also provides an easy means to mount drywall, so no new techniques are needed to hang drywall on the interior. Details on this assembly type can be found here: https://www.greenbuildingadvisor.com/article/furred-continuous-insulation-wall-assembly-to-meet-2021-codes,
Image source: https://www.greenbuildingadvisor.com/article/furred-continuous-insulation-wall-assembly-to-meet-2021-codes
Some builders have objected to continuous exterior insulation because it complicates the installation of exterior air- and weather-resistive barriers. This drives up builder costs, and thus, the client’s. Yet, the two alternative insulation strategies discussed here provide a means to meet these more stringent insulation requirements in the energy codes, yet keep installation simple and in-line with past, familiar construction techniques, which would also reduce costs. These assemblies can help ease builders into higher-performance wall construction, improving the overall performance of future buildings.
The post Alternative Code-compliant Framed Wall Assemblies first appeared on SEDAC | Smart Energy Design Assistance Center at The University of Illinois, Urbana-Champaign.