Control of water intrusion into building assemblies is best achieved by establishing a continuous “drainage plane” that extends across, and in some cases through, all the building enclosure elements and assemblies. These include windows, precast, sealant, flashings, moisture barriers, and roofing systems. Elements such as brick, stone, metal panels, and plaster provide environmental protection as “weather barriers” but should not be considered moisture barriers. An important test of the successful detailing of the “drainage plane” is the ability to trace its “line” throughout all the details of the building enclosure assemblies—without lifting the pencil. In reality, due to gravity’s downward pull on water, detailing to prevent water intrusion can be successful even with some minor discontinuities.
One example is the typical punched window installation with a masonry veneer. Sealant typically ties the wall moisture barrier to the window frame, protecting the head and jambs as shown in Figure A. Properly placed to the frame, this provides for the continuity in the drainage plane. A common detail at the sill is the use of a “pan” to guide water collected and guttered within the window back to the exterior. However, without additional gaskets or sealant, this may not provide a complete barrier against air infiltration. See Figure B. Study your standard details to see how many have hidden paths for air. Similar to a drainage plane, an effective air barrier should be traceable throughout the building enclosure, and not cross an unsealed joint or porous material. Note that the drainage plane and air barriers often can
The successful design and construction of a building’s exterior enclosure defines the aesthetic sense of a building, it secures protection from a variety of weather conditions, and today it is an integral part of strategies for sustainable building design. In recognition of the importance of the building enclosure design, the Building Enclosure Council Initiative was created in May 2004 through a partnership between the American Institute of Architects (AIA) and the Building Enclosure and Environmental Council (BETEC) of the National Institute of Building Science. Its
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mandate is to create a series of BEC chapters across the country to “promote and encourage discussion, training, education, technology, transfer, the exchange of information about local issues and cases, relevant weather conditions, and all matters concerning building enclosures and the related science.” With an initial goal of nine local councils by 2007, there were 17 as of July, with another two or three cities considering establishing their own BEC. Sponsored as an autonomous profit center by local AIA chapters, each local BEC is an interdisciplinary forum with architects, engi-
neers, consultants, manufacturers, contractors, educators, and owners. Texas has two councils, known as BEC Dallas and BEC Houston. To learn more about the BEC program, access information at www.bec-national.org and the National Institute for Building Standards at www.nibs.org. To participate in the Dallas chapter, contact George Blackburn III, AIA, at firstname.lastname@example.org. To join the Houston chaptercontaact or Andy MacPhillimy, AIA, at email@example.com.
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P. 91 image copyright Pali Rao and Andrew Johnson, 2007 istockphoto
Local Councils Promote Education