Gone are the days when inexpensive energy made it possible to design buildings with little regard for energy performance, but constructing environmentally responsible buildings can come at the expense of design freedom. New thin-profile, high-performance insulation is providing architects some additional breathing room-enabling energy code compliance in space-confined areas.
Achieving higher-performing construction and meeting stringent building codes often comes with the added costs of architectural detail modifications and the need for specialized equipment and techniques. Recognizing the need for solutions that meet new requirements but fit easily within standard building processes, Midland, Mich.-based Dow Corning Corp. has developed a new high-performance insulation material. Based on aerogel technology originally used in specialized applications such as aerospace, Dow Corning HPI-1000 Building Insulation Blanket is finding a new niche providing thermal protection in space-restricted construction areas.
Dow Corning HPI-1000 Building Insulation Blanket is a flexible, thin-profile, construction-friendly material that can be cut-to-size on the job site and applied to reduce the thermal bridging at specific locations in a building envelope assembly. It is highly resistant to flame with an ASTM E84 Class A fire rating
(flame spread index 5, smoke developed index 10).
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Figure 2. Dow Corning HPI-1000 Building Insulation Blanket thermally isolates a stainless steel sunshade support. |
Isolating thermal bridging challenges at the Passive House-compliant Kiln Apartments
As energy codes evolve and mandate increased thermal performance in insulation and-in turn, reductions in energy consumption-building construction is subject to a range of local, state and national building standards, as well pressure to comply with voluntary standards and certifications. With help from industry-leading construction innovators, architects are meeting and exceeding those challenges, delivering performance with aesthetics.
With the goal of becoming one of the most energy-efficient multifamily housing buildings in the U.S., the Kiln Apartments building in Portland, Ore., is pursuing the aggressive Passive House standard for energy efficiency. The standard, which originated in Germany, often results in buildings 80 to 90 percent more efficient than the average home in the U.S. For the Kiln Apartments, meeting this standard would require more than simply increasing the amount of conventional insulation-which would be neither practical nor aesthetically pleasing.
One design feature of the Kiln Apartments is sunshade thermal shims that were installed like visors on the top edge of the building’s windows. Bolted to the wall, the 18-inch metal shades created thermal bridging challenges, essentially operating as “reverse radiators.” The stringent insulation requirements to meet Passive House standards made minimizing heat loss in this area crucial.
GBD Architects Inc., Portland, worked with Dow Corning to specify Dow Corning HPI-1000 Building Insulation Blanket, which was cut to fit the sunshade attachment area (see Figure 2). Featuring R 9.8 per inch insulation performance, the blanket reduces heat loss and minimizes the potential for thermal bridging-without altering aesthetics of the window shade design.
Predicting performance benefits through modeling
Even when standards are less demanding than those of Passive House, addressing thermal bridging concerns is important. To determine how effective thin-profile blanket insulation can be in mitigating thermal losses, three common construction details were modeled:
- Curtainwall-at-grade detail with the aerogel blanket applied from the neck of the curtainwall to the below-grade rigid insulation, resulting in a reduction in linear thermal transmittance approaching 25 percent.
- Curtainwall jamb at the exterior and interior insulated steel stud assembly with the aerogel blanket applied around the adjacent steel stud and at the wall-to-curtainwall transition, resulting in a reduction in linear thermal transmittance approaching 70 percent.
- Rehabilitated window-wall system with the aerogel blanket at the slab edge and around vertical and horizontal glazing mullions, resulting in a reduction in linear thermal transmittance approaching 53 percent.
Additionally, two conceptual whole-building energy models were run to demonstrate the effect of using building insulation blankets with conventional and higher-performance assemblies to minimize thermal bridging:
- For a building with the glazing system covering 100 percent of the façade area, addition of the aerogel blanket and conventional assemblies resulted in a 3.56 percent energy savings.
- For a façade with curtainwall glazing and a steel stud wall assembly, addition of the aerogel blanket and higher-performing assemblies resulted in a 6.78 percent energy savings.
The determined lineal transmittance values can readily be incorporated into thermal models, eliminating guesswork and improving the predictability of the heat loss, helping architects and builders achieve their sustainability goals without sacrificing design freedom.
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Stanley Yee, LEED AP, is a façade design and construction specialist for Dow Corning Corp., Midland, Mich. For more information, visit www.dowcorning.com/hpinsulation.