According to the latest estimates, construction operations account for 28% of global carbon emissions. A report by the United Nations Intergovernmental Panel on Climate Change found that reducing the energy use of buildings in turn reduces carbon dioxide emissions. One of the best ways to achieve this is to improve the airtightness of building envelopes, the performance of which varies widely. Research by the United States Department of Energy reveals that air leakage accounts for approximately 6% of the total energy used by commercial buildings in the United States. Specifically, approximately 15% of the energy used by commercial building envelopes was due to air leakage. Knowing this, how can building professionals better design, specify and deliver projects that reduce this transmission?
An air barrier reduces airflow between indoor and outdoor environments. It is one component of a complete weather barrier assembly, with a thermal (thermal) barrier and a vapor barrier. The Air Barrier Association of America defines a weather barrier as “a set of assemblies designed to withstand the loads imposed by all weather elements, including sun, wind, airborne debris ‘air, heat, floods, liquid water and water vapour’. — commonly called the building enclosure.
Many materials can perform the function of an air barrier. Since these layers control flows through a building envelope, materials can end up serving multiple functions; for example, a fluid applied membrane can serve as a barrier against water, vapor and air.
The air barriers were one aspect of an impressive environmental strategy undertaken when completing a new building for Credit Human in San Antonio. Designed by architect Don B. McDonald of Kirksey Architecture and built by Joeris, the classically styled center near the bustling Pearl Brewery features eight office floors over four parking levels. The project “uses biophilic principles, high indoor air quality and transparent materials to create an environment that radiates well-being,” according to Kirksey.
Steve Hennigan, Chairman and CEO of Credit Human, intended to create a healthy indoor environment for the company’s employees. This vision, for which Hennigan has set ambitious climate goals, has extended to air leakage. While the US Army Corps of Engineers air tightness standard is 0.25 cfm/sf @ 75 pa, project managers set a target rate of 0.1 cfm/sf @ 75 pa. To ensure this goal was met, Joeris undertook extensive on-site testing and then documented it in an in-depth case study. (The full deliverable is available online.)
To begin with, the curtain wall units were workshop water tested prior to installation. The building, which used Carlisle air and vapor barrier and other sealants, contained 311 envelope penetrations and used 9,184 brick ties, each of which was sealed with Barritech VP to prevent possible air leaks. The flashing and termination sealant have been inspected for “fish blockages” or wrinkles. The basement UMC and center walls were sealed, and a waterproofing and air barrier was installed between the garage levels and the upper interior floors. The cold joints on the underside of the roof were also sealed using a fire-fighting product.
The detailed waterproofing inspection included water testing and selected demolition to observe the movement of water beneath the finished surfaces. TSI Energy Solutions conducted testing using a PosiTest air leak tester in addition to wind tunnel and water testing conducted by others. The results revealed that the tops and bottoms of interior walls were the weakest points for air transmission, and floors in particular, as dust and debris were not removed prior to installation. an acoustic sealant, creating a leak, in addition to the screw heads that were not glued. and floated or covered by an air barrier. Additional small gaps were inspected and filled after installation, such as on exterior sills where a fire resistant sealant was used.
Overall, how was the Credit Human building? Final test results showed an extremely low amount of air leaks, meeting the target set by Hennigan. This was coupled with other sustainability features including geothermal wells, rooftop solar installations and rainwater harvesting. As a result, the LEED Platinum certified facility uses 96% less grid electricity and 97% less municipal water than a typical building of its size. Diligently installing an air barrier reduces a building’s operating expenses throughout its life. It might be a small saving compared to global numbers, but every little bit counts.