educing dependence on fossil Many other energy-saving systems for exist. It has long been estimated that air fuels, cutting greenhouse gas buildings have been developed – too many leakage in typical building construction emissions, and conserving to mention in this paper. An often-over­ accounts for a large percentage of HVAC valuable energy resources – looked and highly effective way to save ener­ energy consumption. Because of this these are all hot-button gy is to reduce building envelope air leak­ notion, model energy codes IECC3 and issues discussed regularly age. In typical envelope construction, where ASHRAE 90.1 and 90.24 establish require­ Rover the airwaves and in publications. While many types of materials and assemblies are ments for airtightness of fenestration and virtually everyone can agree that these are joined together, countless air-leak paths prescribe sealing of any direct air-leak important issues, there is much dis­ paths through the building envelope. agreement on which remedies to pursue. Constructing more airtight buildings As we live and work largely in a built to save energy seems like an obvious environment, much of the nation’s ener­ solution. A relatively recent study by gy goes toward heating, cooling, lighting, NIST entitled “NISTIR 7238, Investigation and countless other important opera- of the Impact of Commercial Building tions within buildings. According to the Envelope Airtightness on HVAC Energy Alliance to Save Energy,1 residential and Use,”5 confirms that constructing a more commercial buildings use 40% of U.S. airtight building envelope lowers energy energy and contribute to about 38% of consumption for HVAC functions. carbon dioxide emissions. With this Annual energy savings approach 40%, information, one can see that energy use according to the study. Although the pre- by buildings dramatically impacts overall viously mentioned IECC and ASHRAE U.S. energy use. Reducing energy use by codes indicate that airtight construction buildings is important, not only for the is desirable, it is not mandated by these financial savings of building owners, but codes. That is because the IECC and because it would reduce overall U.S. ASHRAE codes do not establish require- energy use, which in turn would reduce ments for airtightness of opaque assem­ consumption of fossil fuels and cut blies or of the building envelope. greenhouse gas emissions. Building code air barrier require- Building codes impacting energy use ments take envelope construction to a in buildings, special programs like higher level by mandating a minimum LEED,2 and energy-conscious design all airtightness level and giving means and provide methods of constructing more methods to achieve it. Canada’s National energy-efficient buildings. To build a Building Code (NBC) has required air more energy-efficient building, there is barriers for more than a decade. The usually emphasis on incorporating more Photo 1: Carlisle Coatings and Waterproofing’s energy code for Massachusetts, entitled insulation and using energy-efficient 705 Self-adhering Vapor and Barrier System “780 CMR Energy Code for Commercial HVAC systems, appliances, and lighting. being applied to a new building. and High-Rise Residential New Con-

S EPTEMBER 2007 I NTERFACE • 21 nificance, even though very few jurisdic­ tions actually require them. NBC and 780 CMR are considered established model codes for air barriers. Design pro­ fessionals, product manufacturers, con­ sultants, and spec writers use the afore­ mentioned codes as the basis for writing air barrier guide specifications. As a result, countless projects across the U.S. have been completed with air barriers that were effectively specified with 780 CMR or NBC. In fact, as a result of these air barri­ er model codes and projects, a national air barrier industry has emerged, sup­ ported by product manufacturers, design professionals, contractors, con­ sultants, professional organizations, and others. As the use of air barriers has entered the mainstream, CSI’s Master- Format® 20047 has assigned a Level 2 section number, 07 27 00, for air barri­ ers, and five Level-3 section numbers for Figure 1 common types of air barriers. Nationally, many building owners have embraced the struction,”6 has included requirements for directly from the language of the NBC. The benefits of air barriers and have paid for air barriers in Chapter 13 of the code since air barrier requirements of 780 CMR appear them to be installed. 2001. The air barrier language in the as seen above (see Figure 1). Note that the established air barrier Massachusetts code was adopted almost Air barriers have achieved national sig­ codes do not say what materials or products to use as air barriers. The codes indicate that an air barrier needs to be continuous, durable, withstand design pressures, accommodate movement, and be composed of materials having an air permeability of not more than 0.004 CFM/ft2 at 1.57 PSF. Air permeability, commonly measured with ASTM E 2178,8 is used to qualify mate­ rials as air barriers by measuring the flow of air through them at a given pressure differ­ ential. A great number of materials exhibit low enough air permeability to be consid­ ered air barriers, including: half-inch dry­ wall, glass, steel, poured concrete, plywood, extruded polystyrene insulation (XPS), spray polyurethane foam, 6-mil polyethyl­ ene sheeting, specialty sheet building wraps, modified bitumen self-adhering sheets, and certain liquid-applied mem­ branes. Materials that allow largely uninhibited passage of air exhibit a high level of air per­ meability and are NOT air barriers. Examples of these include most brick and mortar assemblies, non-glazed concrete block, batt insulation, expanded poly­ styrene insulation, perforated house wraps, and building paper. When all of the provisions of the model air barrier codes are considered, the selec­ tion of air barrier materials becomes more

22 • INTERFACE S EPTEMBER 2007 wall and is covered by the building’s exteri­ or cladding. This is the same location where one would find building paper or house wrap as a water-resistive barrier in conven­ tional construction. Typical air barrier membrane products employed on these projects include peel-and-stick sheets, liquid-applied coatings, mechanically attached sheets, or spray-applied polyure­ thane foam. The air barrier membrane on the walls either terminates onto a poured concrete footer or ties into below-grade waterproofing or dampproofing. Then the air barrier membrane on the wall is either joined directly to the roofing membrane, it is joined to a special roofing air barrier underlayment, or it terminates onto an air­ tight roof deck. Not all wall assemblies require a full coverage membrane to meet the air barrier requirements. For example, walls con­ structed of poured concrete or air barrier type sheathing with joints securely sealed can meet the air barrier requirements as long as there are provisions made to seal the walls at openings and around penetra­ tions to the roof and foundation. Regardless of materials and methods selected, the greatest challenge to providing an effective air barrier is installation. With all of the common building materials that Photo 2: Carlisle Coatings and Waterproofing’s 705 Self-adhering Vapor and Barrier System qualify as air barriers, it’s easy to imagine being applied to a new building. that the challenge lies not in selecting air­ tight materials, but in finding a way to put focused. In particular, the requirement for when it is properly installed on a project? A all these materials together without leaving continuity is the most difficult to achieve. common approach is full coverage of the holes or having holes eventually manifest For example, 6-mil polyethylene sheeting, walls with an airtight polymeric membrane themselves. To this end, ASTM has devel­ even though it qualifies as an air barrier, that is fully supported by the wall surfaces oped a standard, designated E 2357,9 for generally cannot meet the provisions of the and either fully adhered or securely evaluating performance of air barrier air barrier code as installed in practice. attached by other means. Tight seals to the assemblies. Another standard by the same That is because it is virtually impossible to air barrier membrane are made around win­ organization, ASTM E 1186,10 is useful for install 6-mil poly without holes or gaps in dows, doors, and mechanical and electrical performing field inspection of air barrier its typical location, which is on the inside penetrations. The air barrier membrane is assemblies. ASTM also has standards for surface of the wall and ceiling studs. In this placed on the exterior side of the structural measuring air and watertightness of field- location, 6-mil poly is unsupported in the span between studs, is not sealed at over­ laps between sheets, and has many mechanical and electrical penetrations through it. Even if one installs the poly sheets meticulously to seal the laps and penetrations, how will it be joined to the roof and foundation, and how will it be made continuous between floors? The same problems exist when trying to use interior drywall as an air barrier. In addition to material choice, location within the building envelope and method of installation are cru­ cial factors for delivering effective air barri­ ers. So, what does an air barrier look like

S EPTEMBER 2007 I NTERFACE • 23 Photo 3: Carlisle Coatings and Waterproofing’s Barriseal Liquid-Applied Air Barrier being applied to Lawrence High School in Lawrence, Massachusetts.

constructed mock-ups as locate these properly in the envelope assem­ well as standards for mea­ bly so as not to “trap” moisture. suring whole-building air- In some regions of the country, vapor tightness. With a multi- barriers are required by code in the exterior tiered approach – escalating envelope assembly. A material that is both from air barrier material an air barrier and a vapor barrier can qualification to air barrier simultaneously perform these necessary assembly qualification to functions. Some air barriers are vapor per- evaluation of whole-building meable, so they block airflow and are often airtightness – a systematic water resistant, yet they allow moisture and standardized method of vapor to pass through. In any case, air bar- delivering an airtight enve­ riers must not be confused with vapor bar- lope can be followed. riers, as these two functions must be con- Materials employed as sidered separately. Both systems function- air barriers can have multi­ ing as vapor-permeable air barriers and ple functions. Often, they those functioning as air and vapor barriers are also water resistant or can be used successfully with proper enve­ waterproof because of their lope design and installation. composition and intended Air barriers provide benefits other than area of installation. In this just energy savings. They also enable a case, they perform a dual more comfortable interior environment by function as an air barrier allowing more controllability of the HVAC and a water-resistive barri­ system. Air barriers can also provide a er. Some air barriers are also healthier interior environment while ex- vapor barriers, in which tending building life. Consider that a seri­ case care must be taken to ous consequence of air leakage through the Reroofing building envelope is the wetting of non­ moisture-resistant materials through con­ densation. Free air movement through the building envelope can inadvertently move a lot of moisture. For example, heavy conden­ sation can form as a result of movement of inside heated and humidified air toward the cold exterior in a cold climate. Conversely, in a warm climate, condensation forms from movement of hot and humid air toward the cool, air-conditioned interior. Persistent condensation can cause mold growth, decay, and corrosion, which in turn can cause health problems for occupants and premature building deterioration. Studies by the Canadian Mortgage and Housing Corporation (CMHC)11 and Oak Ridge National Laboratories (ORNL),12 as well as investigations performed by individ­ ual building envelope consulting firms reveal the damaging effects of moisture Photo 4: Carlisle Coatings and Waterproofing’s Barriseal Liquid-Applied Air Barrier being from condensation as a result of air leakage applied to Lawrence High School in Lawrence, Massachusetts. across building envelope assemblies. Specifying an air barrier and assuring its proper installation can be a monumental considered the universal air barrier Massachusetts energy code. Since then, feat. While manufacturers of air barrier resource. ABAA was formed in 2001 as a this organization has grown, with national materials are obvious resources for assis­ group of professionals whose mission was membership from many companies and tance with their proprietary systems, the Air to provide guidance on how to meet the new professions. ABAA’s Web site (www.airbar­ Barrier Association of America (ABAA)13 is air barrier requirements in the rier.org) contains guide specifications for various types of air barriers, a library of MSPageID=220. www.csinet.org. technical articles, member directory, and 3 International Energy Conservation 8 ASTM E 2178, Standard Test other important information. ABAA also Code 2006. Method for Air Permeance of trains and certifies air barrier installers and 4 American Society of Heating, Building Materials. provides building owners with a quality Refrigerating and Air-Conditioning 9 ASTM E 2357, Standard Test assurance program (QAP) to assist in deliv­ Engineers (ASHRAE) 90.1 Energy Method for Determining Air Leakage ery of a quality air barrier on a specific pro­ Standard for Buildings Except Low- of Air Barrier Assemblies. ject. Rise Residential Buildings, 90.2 10 ASTM E 1186, Standard Practices Energy Efficient Design of Low-Rise for Air Leakage Site Detection in Conclusion Residential Buildings. Building Envelopes and Air Barrier Air barriers in building envelope con­ 5 NISTIR 7238. The full report is pub­ Systems. struction provide significant HVAC energy licly available at www.fire.nist.gov/ 11 Canadian Mortgage and Housing savings. Buildings consume nearly half of bfrlpubs/build05/PDF/b05007.pdf. Corporation, www.cmhc-schl.gc.ca/. U.S. energy use, so installing air barriers in 6 CMR 780 is accessible to the public 12 Oak Ridge National Laboratories buildings can dramatically impact national at www.mass.gov/bbrs/energy.htm. (ORNL), www.ornl.gov/sci/btc/ energy consumption. Constructing build­ 7 MasterFormat® 2004 is available for search.shtm. ings with barriers can contribute signifi­ purchase from the Construction 13 Air Barrier Association of America, cantly toward efforts to reduce U.S. depen­ Specifications Institute (CSI) at www.airbarrier.org. dence on fossil fuels and can lower green­ house gas emissions and lessen consump­ tion of valuable energy resources. Air barri­ Brian Carey ers also enable a more comfortable and healthy interior. Brian Carey is employed by Carlisle Coatings and Waterproofing, where he has assumed the role of air and References vapor barrier product manager for the past three years. He 1 The Alliance to Save Energy charter has worked in the coatings, sealants, and adhesives busi­ and published information can be ness, serving the construction and manufacturing sectors accessed at www.ase.org/content/ since 1994. Carey holds a BS in chemical engineering from article/detail/2356. the University of Michigan in Ann Arbor. He also serves as 2 LEED (Leadership in Energy and technical committee chairman for the Air Barrier Association Environmental Design) programs for of America (ABAA) and holds a seat on the board of directors new construction can be accessed at of that organization. Carey is also a member of the Construction Specifications Institute www.usgbc.org/DisplayPage.aspx?C (CSI) and the American Architectural Manufacturers Association.