Determining Air Barrier Performance

Transcription

1 solutions for the construction industry december 2009 Determining Air Barrier Performance The Offi cial Magazine of the q Construction Specifi cations Institute also in this issue Using CPVC for Industrial Piping Seismic Tests for Brick Assemblies Linking with Keynotes

2 Testing Mechanically Fastened Air Barrier Systems Under Wind Pressure by maria Spinu, phd, CSi, leed ap, and alan learned, phd All photos courtesy DuPont ABOUT 40 PERCENT OF THE WORLD S ENERGY IS CONSUMED BY THE BUILDING SECTOR, AND ABOUT 37 PERCENT OF THIS IS FOR HEATING, COOLING, AND VENTILATION. 1 SINCE AIR LEAKAGE HAS A SIGNIFICANT EFFECT ON HVAC USE, DESIGN PROFESSIONALS MUST UNDERSTAND HOW A CONTINUOUS AIR BARRIER SYSTEM CONTRIBUTES TO AN ENERGY-EFFICIENT ENVELOPE. Air infiltration is a property that is inherent to each material and can be measured in the lab, but whole building air leakage is highly dependent on field installation and quality of workmanship. Testing of air barrier assemblies is an important intermediate step for developing proper installation guidelines and best practices. The standard method for testing of air barrier assemblies is ASTM E (2000), Standard Specification for an Air Barrier Material or System for Low-rise Framed Building Walls. A more recent standard for determining air leakage of air barrier assemblies in commercial enclosures ASTM E , Standard Test Method for Determining Air Leakage of Air Barrier Assemblies requires testing under significantly more stringent conditions. This article reviews test methods and performance requirements for air barriers, with special focus on assemblies constructed with mechanically fastened membranes (i.e. building wraps). ASTM E 2357 testing of assemblies constructed with commercial-grade spun bonded polyolefin (SBP) membranes shows these systems outperform requirements for air barrier assemblies, when installed per the manufacturer s instructions. This allows a tighter and more energy-efficient building envelope. Air infiltration and air leakage This section gives a brief summary of the test methods and requirements for air barrier materials, assemblies, and whole buildings. 2 Air barrier materials Air barrier materials are defined by their level of air permeance, which is the amount of air that migrates through a material. The standard test method for determining air infiltration in this context is ASTM E 2178, Standard Test Method for Air Permeance of Building Materials. Performance requirements for air barrier materials have been specified in the National Building Code of Canada (NBC) since NBC requires air barriers have an air permeance not to exceed 0.02 L/s m 75 Pa (0.004 cfm/sf under a pressure differential of 0.3 in. H 2 O [1.57 psf]). In 2001, Massachusetts became the first state to adopt an air barrier code in the United States with similar requirements as NBC. Other states (Georgia, Minnesota, Rhode Island, Washington, and Wisconsin) and agencies (e.g. U.S. Army Corp of Engineers [USACE] and General Services Administration [GSA]) are beginning to mandate air barriers and enforce airtightness standards. Few other states are developing such codes. A national standard for air barriers is needed. American Society of Heating, Refrigerating, and Air-conditioning Engineers

3 (ASHRAE) 90.1, Energy Standard for Buildings Except Low-rise Residential Buildings, has been developing an air barrier standard for the past four years. The last public review of the ASHRAE 90.1 air barrier proposal was published June 19, Many common building materials meet the air permeance requirement. A few examples are: plywood minimum 10 mm ( 3 8 in.); oriented strandboard (OSB) minimum 10 mm; extruded polystyrene (XPS) insulation board minimum 19 mm ( 3 4 in.); foil-faced urethane insulation board minimum 12 mm ( 1 2 in.); exterior gypsum sheathing or interior gypsum board minimum 12 mm; cement board minimum 12 mm; built-up roofing (BUR) membrane; modified bituminous (mod-bit) roof membrane; fully adhered single-ply roof membrane; a portland cement/sand parge, stucco, or gypsum plaster minimum 16 mm ( 5 8 in.) thick; cast-in-place (CIP) and precast concrete; and sheet metal. Materials specifically designed as air barriers include premanufactured sheet structures (i.e. mechanically fastened or self-adhered membranes) or fluid-applied membranes and foams. Some weather-resistive barriers (WRBs) also meet the material requirements for air barriers, however many others (including building paper and perforated wraps) do not. Air barrier assemblies Air barrier assemblies are made up of primary air barrier materials and accessories (e.g. primers, sealants, tapes, flashing, mechanical fasteners, etc.) that provide a well-designed air barrier systems can improve a building s energy efficiency, but proper field installation is crucial. continuous designated plane to the movement of air through portions of building enclosure assemblies. The air leakage rate for assemblies is the sum of air infiltration through both materials and the unintended holes or gaps at penetrations and transitions. As mentioned, ASTM E 1677 and ASTM E 2357 are the two accepted standards for testing air barrier assemblies under conditions simulating actual use. ASTM E 1677 describes the testing method and includes performance criteria for air leakage rate of air barrier assemblies not to exceed 0.3 L/s m 75 Pa (0.06 cfm/sf at 0.3 in. H 2 O [1.57 psf]) when tested in accordance with ASTM E 283, Test Method for Determining the Rate of Air Leakage Through Exterior Windows, Curtain Walls, and Doors Under Specified Pressure Differences Across the Specimen. ASTM E 2357 requires significantly more stringent test conditions, but does not specify an air leakage rate for air barrier assemblies. Instead, the air permeance values at 75 Pa for the exfiltration and infiltration conditions Figure 1 Summary CompariSon Between astm e 1677 and astm e 2357 ASTM E ASTM Number of test specimens and configuration Conditions for air leakage testing Pressure-loading schedule One specimen: Opaque Wall (8 x 8-ft walls) Single test pressure: 75 Pa (1.56 psf); 40 km/h (25 mph) (Positive pressure) Sustained loads up to +500 Pa (10.4 psf); km/h (65 mph) (Positive pressure) Test two of the three specimens (8 x 8-ft walls): 1 Opaque wall 2 Wall with penetrations 3 Wall-foundation interface Seven test pressures: +/ 25 Pa (0.56 psf); 24 km/h (15 mph) +/ 50 Pa (1.04 psf); 32 km/h (20 mph) +/ 75 Pa (1.56 psf); 40 km/h (25 mph) +/ 100 Pa (2.09 psf); 46 km/h (28.8 mph) +/ 150 Pa (3.24 psf); 56 km/h (35 mph) +/ 250 Pa (5.23 psf); 73 km/h (45.6 mph) +/ 300 Pa (6.24 psf); 80.5 km/h (50 mph) (Positive & negative pressures) Sustained: +/- 600 Pa (12.5 psf); 113 km/h (71 mph) Cyclic: +/- 800 Pa (16.7 psf); 130 km/h (81 mph) Gust: +/ Pa (25 psf); 161 km/h (100 mph) (Positive & negative pressures)

4 Figure 2 are used to establish the system air leakage rating. ASHRAE 90.1 s air barrier proposal specifies performance criteria for average air leakage rate of air barrier assemblies in other words, not to exceed 0.2 L/s m 75 Pa (0.04 cfm/sf under a pressure differential of 0.3 in. H 2 O [1.57 psf]) when tested in accordance with ASTM E 1677 or ASTM E The International Building Code (IBC) requires a continuous weather-resistive barrier to protect against water intrusion. However, for a WRB to also perform as an air barrier, it must: meet the material permeance criteria (e.g. not to exceed 0.02 L/s m 75 Pa (0.004 cfm/sf under a pressure differential of 0.3 in. H 2 O [1.57 psf]); and be installed in such a manner as to meet air leakage requirements for air barrier assemblies (e.g. not to exceed 0.3 L/s m 75 Pa (0.06 cfm/sf at 0.3 in. H 2 O [1.57 psf]). 3 Whole building air leakage The standard test method for whole building air leakage is ASTM E , Standard Test Method for Determining Air Leakage Rate by Fan Pressurization (e.g. the blower door test). Currently there are no criteria for air leakage rate of whole buildings. For example, ASHRAE 90.1 requires sealing, caulking, gasketing, or weatherstripping at joints and interfaces, but does not specify an air leakage rate. The ASHRAE 90.1 air barrier proposal includes criteria for air leakage rate of air barrier materials and assemblies, but not for whole buildings. The only guideline for whole building air leakage rate is provided by the U.S. Army Corps of Engineers, which requires blower door testing of all new buildings and an average air leakage rate not to exceed 1.25 L/s m 75 Pa (0.25 cfm/sf at a pressure differential of 0.3 in. H 2 O [1.57 psf]), when tested in accordance with ASTM E or an equivalent approved method. The USACE-proposed whole building air leakage rate was based on values from field testing available to date, 4 and are achievable with current technologies using best practices. the configuration of the three wall assemblies for astm e 2357 testing. Testing of commercial air barrier assemblies The ultimate goal when using an air barrier is to reduce air leakage both in (i.e. infiltration) and out (i.e. exfiltration) of the building, and to achieve a tight envelope. Testing of air barrier materials, while important, is not enough to ensure whole building performance because actual installation methods are critical. On the other hand, while whole building testing can be done, it might be too late to find out the project leaks after it has been completed. Testing of air barrier assemblies is a very important intermediate step for establishing the best installation methods for a system that performs under use conditions. Figure 1 provides a summary comparison between the two test methods currently accepted for air barrier assemblies. As mentioned, this article focuses on the more stringent ASTM E , which is a laboratory procedure, but may also be applied to site mockups. It requires up to three specimens, each additionally representing different

5 field conditions. Figure 2 shows the configurations of the three test assemblies. Measurements must be performed on two of the three test specimen. (Specimen 3 is optional and may be combined with Specimen 2.) ASTM E 2357 requires at least seven measurements of air leakage rate under both positive and negative pressures (i.e. infiltration/exfiltration) at each of the air pressure differences across the test specimen indicated in Figure 1. Pressure loading schedule After the initial air leakage testing, ASTM E 2357 requires each specimen be exposed to a structural loading schedule (i.e. conditioning). The wall assembly s structural loading is based on the assumption the air barrier: takes the full wind loads (i.e. pressure-equalized façade systems); experiences repeated cycling of high positive and negative pressure loads during its service life (i.e. thousand cycles); and experiences two severe storms in the first 15 years in service. Figure 3 shows the pressure load profiles for sustained loads, cyclic loads, and gust loads at pressures indicated in Figure 1. Figure 3 astm e 2357 wind loading schedule for sustained, cyclic, and gust loads. Figure 4 opaque wall assemblies constructed with spun bonded polyolefin (SBp), using screws/washers or brick ties as fasteners. Post-conditioning air permeance The air leakage test is repeated after the pressure loading, and the post-conditioning air leakage rates at 75 Pa are used to establish the assembly air leakage rating. Deflection measurements ASTM E 2357 requires the maximum deflections of the air barrier material and test specimen be measured following the pressure load testing. These deflection measurements must be recorded at wind pressures equal to the wind design values for the geographical areas (i.e. up to 1440 Pa [30 psf] or equivalent wind speed of 175 km/h [109 mph]). 5 Testing of wall assemblies with mechanically fastened air barriers Based on the application method, air barrier materials are classified as fluid-applied, self-adhered, or mechanically fastened membranes (i.e. building wraps). Installation details are specific to each type of air barrier and vary among manufacturers. Improper installation could lead to failure of any type of air barrier system. However, for building wraps, the failure caused by improper installation could be more visible, fostering a misconception building wraps do not perform as air barriers. Not all building wraps meet ASTM E 2357 performance criteria. Each manufacturer must specify all materials and components as well as how to deal with penetrations and transitions to achieve a continuous air barrier assembly. Issues such as compatibility and durability must also be addressed by the manufacturer (rather than the design professional using a trial and error method). Due to the many factors affecting performance in use, testing must be done for the specific air barrier assembly, rather than generally. Typical wall assemblies using commercial-grade SBP This article describes testing by an independent third-party laboratory of air barrier assemblies constructed with commercial-grade spun bonded polyolefins. More than two dozen wall assemblies (opaque and penetrated walls) representative of target commercial installations were built and tested to gauge their performance against the ASTM E 2357 requirements for air barrier assemblies and establish the best installation practices. Opaque wall assemblies (Specimen 1) Typical commercial walls were constructed with 2x6 18- gage steel studs (406 mm [16 in.] on center [oc]) and sheathed with exterior gypsum board. Commercialgrade SBP membranes were installed with the recommended horizontal and vertical seams, which were sealed with 76-mm (3-in.) tape, fastened into the steel studs with screws and or 51-mm (1 ¼ or 2-in.) gasketed metal or plastic washers spaced 305 or 457 mm (12 or 18 in.) oc. Brick ties with flashing patches, spaced 305 or 406 mm (16 in.) oc, were also tested as the permanent fasteners. Figure 4 shows representative pictures of the opaque wall assemblies constructed and tested by an independent third-party laboratory.

6 The air infiltration rate measured for both specimens was less than 0.05 L/s m 2 (0.01 cfm/sf) at all test pressures, under both positive and negative pressure differential. Both specimens significantly outperformed the ASHRAE 90.1 and ASTM E 1677 requirements. astm testing of air barrier assemblies is an important step for developing proper installation guidelines and best practices. Wall assemblies with penetrations (Specimen 2) The penetrated walls were the same construction as Specimen 1, but included standard penetrations as required in ASTM E 2357: window, junction boxes, duct, and pipe. The steel octagonal box and 102-mm (4-in.) polyvinyl chloride (PVC) electrical box were reinforced with tape and sealed with a commercialgrade sealant around the perimeter. The 38-mm (1.5-in.) PVC pipe was sealed using flexible flashing around the perimeter. Flexible flashing was installed at the head and sill of the window, and straight flashing was installed at both jambs. The entire window perimeter was sealed with a commercial-grade sealant. Figure 5 shows pictures of typical Specimen 2 wall assemblies, built and tested by an independent third-party laboratory. Air leakage test The initial air leakage rate was measured under the following sustained wind conditions, under both positive and negative pressure differential: + / 25 Pa (0.56 psf) or equivalent wind speed of 24 km/h (15 mph); + / 50 Pa (1.04 psf) or 32 km/h (20 mph); + / 75 Pa (1.56 psf) or 40 km/h (25 mph); + / 100 Pa (2.09 psf) or 46 km/h (28.8 mph); + / 150 Pa (3.24 psf) or 56 km/h (35 mph); + / 250 Pa (5.23 psf) or 73 km/h (45.6 mph); and + / 300 Pa (6.24 psf) or 80.5 km/h (50 mph). Figure 5 penetrated wall assemblies constructed with SBp, using screws/washers or brick ties as fasteners. also, flashing of penetrations. Pressure loading schedule After the initial air leakage testing, each specimen was exposed to a structural loading schedule (conditioning), which included: sustained loads for 60 minutes under positive and negative deformation: +/ 600 Pa (12.5 psf), or equivalent wind speed of km/h (70 mph); cyclic loading for 1000 cycles under positive and negative pressure: +/ 800 Pa (16.7 psf), or 130 km/h (81 mph); and gust loads for a three-second load under positive and negative pressure: +/ 1200 Pa (25 psf), or about 161 km/h (100 mph). After each loading stage, the wall assemblies were inspected for signs of fracture, delamination, loosening of fasteners, or other damage per ASTM E 2357 requirements. Neither specimen showed any damage under the above structural load conditions. Post-conditioning air permeance Following the structural loading test, the wall specimens were subjected to the same pressure conditions as the original air leakage testing; the infiltration rate was measured again under sustained wind conditions, positive and negative pressures. The air leakage rate for the two specimens was less than 0.05 L/s m 2 (0.01 cfm/sf) at all seven test pressures and under both positive and negative pressures. The post-conditioning air leakage rate at 75 Pa gives the air leakage rating for this assembly of less than 0.05 L/s m 75 Pa ( in. H 2 O [1.57 psf]). Both specimens significantly outperformed the requirement for air barrier assemblies per ASHRAE 90.1 that is, less than 0.2 L/s m 75 Pa ( in. H 2 O [1.57 psf]). They also outperformed ASTM E 1677, which is less than 0.3 L/s m 75 Pa ( in. H 2 O [1.57 psf]). Deflection measurements The specimens were then subjected to positive and negative deflection loads of +/ 1440 Pa (30.1 psf) or equivalent wind speed of about 176 km/h (109.3 mph). The total deflection measured under negative load was less than 25 mm (1 in.). Further, under these extreme pressure loads, the entire test assembly (including structural framing) had a deflection of more than 38 mm (1.5 in.), once again indicating the extreme structural load conditions required by ASTM E Typical structural design for commercial buildings would require additional bracing or narrower stud spacing to limit the wall deflection on the structure. Testing beyond ASTM E 2357 While ASTM E 2357 uses a very rigorous set of conditions for testing of air barrier assemblies, the high-

7 performance capability of properly installed SBP mechanically fastened wrap systems can be seen in testing beyond these parameters. After completing the ASTM E 2357 deflection test, wall assemblies were subjected to an additional air leakage test. Once again, the air infiltration measured for both specimens was less than 0.05 L/s m 75 Pa ( in. H 2 O [1.57 psf]) at all seven test pressures under both positive and negative pressure differential; this means both specimens significantly outperformed the requirement for air barrier assemblies per ASHRAE 90.1 and ASTM E The wall assemblies were then placed in a chamber and exposed to thermal cycling, consisting of 28 cycles between 17 and 82 C (0 and 180 F). The severe range in temperature tests the system s ability to not only handle the extreme temperatures themselves, but also the expansion and contraction forces created around critical interfaces in the assembly throughout the cycle. The robustness of the penetration details and taped seams in particular are stressed during this test. For the wall assembly specimens designed for the highest structural load conditions, pressure loads of up to 4310 Pa (90 psf) or equivalent wind speed of 306 km/h (190 mph) were used to further challenge the assemblies. Air penetration resistance testing (i.e. ASTM E 283) and water penetration resistance testing (i.e. ASTM E 331) was conducted after these severe thermal cycling conditions. The water test consisted of a 15-minute cycle at each of the following pressure differential: 25, 75, and 700 Pa (0.52, 1.56, and psf) or equivalent wind speeds of 23, 40, and 122 km/h (14.4, 25, and 76 mph). The best wall assemblies (employed to develop highperformance installation guidelines) showed no water leakage at the above test pressures and air leakage levels better than the proposed ASHRAE 90.1 limits. In practical terms, this testing demonstrates when the continuous air barrier is designed with recommended system components and installed per manufacturer s instructions, these systems resist the wind pressures and water penetration under expected building movement for the region in which the building is constructed. also pictured on the cover, the Children s Hospital (pittsburgh, pennsylvania) relies on an air barrier system to reduce both its unintended air leakage and its use of mechanical systems for heating and cooling. Figure 6 SCrew FaStenerS and 16 Steel Stud SpaCing Washer size Fastener spacing Allowable pressure 2 metal 2 plastic 1.25 metal psf 188 mph psf 153 mph psf 165 mph psf 133 mph psf 153 mph psf 125 mph * Values presented are maximum allowable pressures. A factor of safety may need to be applied for certain cladding systems. Mechanically fastened wrap installation keys The key to achieving this kind of high performance air barrier and water-resistive barrier system with mechanically fastened wraps is to pay particular attention to the COF installation principles continuity, overlap, and fasteners. Continuity This principle encompasses sealing seams with a durable tape, proper terminations at roof-wall interfaces, wall-to-foundation interfaces, and appropriate details for all penetrations. Overlap This refers to the proper shingling of the materials (air barrier and flashing) to facilitate efficient drainage down the system. Fasteners Fasteners are important both for durability and from an air barrier integrity perspective. Certain types of fasteners, for example slap staples, used in building paper installation methods are very poor choices for a high-performance wrap air barrier system. Cap fasteners of the appropriate design and installed at the appropriate spacing provide excellent performance. Fastener examples and their representative performance limits with wrap systems are shown in Figure 6. Summary Air leakage is one of the factors significantly affecting HVAC energy use. When properly installed, a continuous air barrier system can minimize air leakage into or out of the building. As shown by the research discussed in this article, air infiltration rates measured for air barrier assemblies constructed with commercial-grade spun bonded polyolefin, and tested under severe conditions of ASTM E 2357 standard, can significantly outperform the requirements for air barrier assemblies under ASHRAE 90.1 and ASTM E This work is instrumental in providing valuable information for optimizing the installation methods used for the development of installation guidelines for SBP air barrier systems. cs

8 Notes 1 For more on these statistics, see the May 2009 World Business Council for Sustainable Development (WBCSD) document, Energy Efficiency in Buildings Report. Visit See also the 2008 U.S. Department of Energy (DOE) Buildings Energy Databook at buildingsdatabook.eren.doe.gov. 2 More information on test methods and performance requirements of air barrier materials and assemblies can be found at the Air Barrier Association of America Web site ( 3 For further discussion on role of air and weather-resistive barriers, see the October 2009 Insight Vocabulary by Joseph W. Lstiburek online at At that site, John Straube also provides further information on air barriers via Building Science Digest 014, Air Flow Control in Buildings. For» AdditionAl InformatIon Author buildings, Maria Spinu, PhD, CSI, LEED AP, received her doctorate in polymer science from Virginia Tech and has worked with DuPont for two decades. She currently leads the Building Innovations group s building science and sustainability initiatives. Spinu is a member of the ASHRAE 90.1 Committee and envelope subcommittee, and has authored 15 patents. Spinu can be contacted via at [email protected]. Alan Learned, PhD, received his B.Sc. in Chemistry from Sterling College and his doctorate in organic chemistry from the University of Utah. In 1987, he joined DuPont, where he has received numerous awards and patents for new product, technology, and process development. Learned is currently the commercial technology development leader for the DuPont Building Innovations business. He can be contacted via at [email protected]. Abstract Air leakage is one of the factors significantly affecting HVAC energy use. This article reviews test methods and performance requirements for air barrier materials, assemblies, and whole further discussion on vapor permeability of air barriers and weather barriers, see co-author Spinu s article, To Be or Not to Be Vapor-permeable? in the April 2007 issue of The Construction Specifier. Visit and select Archives. 4 See National Institute of Standards and Technology Interagency Report (NISTIR) 7238, Investigation of the Impact of Commercial Building Envelope Airtightness on HVAC Energy Use, by Steven J. Emmerich, Tim McDowell, and Wagdy Anis. See also Airtightness of Commercial Buildings in the U.S., by Steven J. Emmerich and Andrew K. Persily and sponsored by DOE s Office of Building Technologies under Agreement No. DE-A01EE All equivalent wind speeds in this article should be considered as approximate. with special focus on testing of systems constructed with mechanically fastened membranes. Current ASTM methods show commercial-grade spun bonded polyolefin (SBP) membranes can outperform current requirements for air barrier assemblies when installed per the manufacturer. MasterFormat No Air Barriers UniFormat No. B2010 Exterior Wall Vapor Retarders, Air Barriers, and Insulation Key Words Division 07 Air barrier systems Air leakage ASTM International Building wrap Spun bonded polyolefin Contents of The Construction Specifier are copyrighted and are reproduced by Foster Printing Service with consent of Kenilworth Media Inc. The publisher and The Construction Specifications Institute shall not be liable for any of the views expressed by the authors, nor shall these opinions necessarily reflect those of the publisher and The Construction Specifications Institute. P: Tyvek W: