by Lee Durston
Uptime June/July 2008
Architects, contractors, engineers and building owner-developers are beginning to see a new push to include air barriers into their structures. This trend has brought about numerous questions and very little in the way of answers. For one, the International Energy Conservation Code (IECC) and several state energy codes— Massachusetts,Wisconsin and Michigan , with more expected to follow—now require the use of air barriers. More importantly, energy efficiency and occupant comfort—two key ingredients of sustainable design—are driving the use of air barriers across market sectors.
What an air barrier actually is and does is not always well understood by many professionals – it is not a vapor barrier…at least not in all cases. Needless to say, air barrier systems’ performance in the exterior walls, foundation/floors and roof systems are getting much more attention in the construction of high performance buildings.
In fact, air-barrier systems in nonresidential buildings are estimated to reduce air leakage by up to 83 percent, save on gas bills by more than 40 percent and cut down on electrical consumption in excess of 25 percent, according to simulations by the National Institute of Standards and Technology (NIST) of typical buildings without air barriers.
Although the results of this particular NIST study have not been field tested, the results are compelling. Manufacturers and groups such as the Building Enclosure Council (BEC) have publicly confirmed the importance of air barriers to meeting energy benchmarks and to building performance and sustainability in general. Without an effective, continuous air-barrier system, conditioned air tends to escape through the building envelope, and the heating, ventilation and air-conditioning (HVAC) system has to work harder to keep the indoor environment comfortable.
And, as the NIST report demonstrated, harder-working HVAC means higher energy bills. In fact, the statistics from NIST and other academic and professional research groups have not only caught the attention of certain entities—such as the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE) and code officials in Massachusetts, Michigan and Wisconsin—but they have led to new awareness of the fact that air barriers also can increase both the longevity and durability of the building envelope. Considering that walls and roofs account for approximately 25 percent of total building construction costs, bolstering the building envelope’s quality makes a lot of sense both from a life cycle cost analysis stance and building health stance.
To ensure that air-barrier materials meet the needs of rigorous demands, specifiers and building teams can refer to laboratory testing for meeting such standards as ASTM E-2357-05, which tests air-barrier assemblies for air leakage and ASTM 2178-03, which tests for air leakage of materials. But this alone does not guarantee that the materials will be constructed to bring about an air-tight structure. A new form of testing has developed for commercial structures and has been incorporated in residential applications for some years now. Real-world metrics testing incorporating pressurization systems (industrial blower-doors) and infrared thermal imaging allows for a rate leakage test (fan) for the building envelope, and a locate test (infrared) to find voids in the air barrier assembly.
In an effort to provide for the construction of a continuous air barrier in new construction or to test existing buildings for air-tightness and provide remedial recommendations where necessary, a host of services are now available, including:
• Design and pre-construction observation during construction, pre-test visits, air-tightness testing, air leakage investigation and advice on effective remedial works should the building fail to achieve the required standard.
Peer review of the proposed construction methods and materials can be undertaken by analyzing drawings and specifications and providing feedback where warranted.
• Site visits to observe construction quality and detailing to confirm that an effective airtight barrier is being provided.
Air-tightness tests are preceded by the issuing of a pre-test inspection list. Alternatively, a separate pre-test walk-thru can be made to ensure the test itself is carried out quickly with a minimum of disruption.
• Air-tightness testing, providing pressurization equipment ranging from modular single door fans for testing small buildings and rooms within buildings (Figure 1), to large multiple fan systems for testing larger buildings (Figure 2) in accordance with ASTM’s E 779 (2003) and E-1827-96 (2002). All tests can normally be carried out in one day, with the building pressurization lasting around one hour. A pass or fail can generally be confirmed while on site, and a full written report issued within 5 working days of completing the test.
• Air leakage investigation and remedial works in case the building fails to achieve the required air-tightness standard (see Figures 3,4 and 5). Further investigation can be undertaken while on site to pin point the causes of the failure using infrared imaging, envelope testing in accordance with ISO 6781:1983 and ASTM C1060-90(1997), and smoke testing methods. Remedial works can then be agreed upon to bring the building envelope up to the necessary standard prior to carrying out a retest. In the end, buildings can be tested to verify performance levels based on codes, or requirements. Additionally, testing can be performed to achieve additional LEED credits through innovation points.
Although energy costs have been the final factor to the requirement of air barriers, in my opinion, it is move in the right direction. Air leakage through the building envelope can lead to unnecessary heat loss in winter or heat gain in summer, condensation and moisture damage in hidden cavities, rain penetration, poor indoor temperature and humidity control, and excessive energy consumption. As awareness increases, the air barrier will be specified more and more and retro-active air-tightness measures on existing buildings will become the norm.
Don’t wait for the codes to require it, do the smart thing now.
Lee Durston is the Director of Building Sciences at BCRA in Tacoma, WA
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