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The goal of the Building Performance Knowledge Community (BPKC) is to promote architects as leaders in the application of technical design for building performance; in the use of high-performance design criteria, codes, and standards; and in programming, designing and managing building performance. To advance, disseminate, and advocate—to the architecture profession, AIA members, building owners, the construction industry, the academy, and the public—design practices that create buildings that are healthy, energy efficient, and durable.

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Building Envelope Air Barriers

  • 1.  Building Envelope Air Barriers

    Posted 04-12-2020 19:07

    Chapter 3

    The third element for energy efficiency of the building envelope is the air barrier.  It is the latest building envelope barrier system to be required by the Building Code and the least understood relative to its design, installation, and performance verification.  Air movement through the building envelope (infiltration and exfiltration) transfers energy, as well as moving water vapor and pollutants.  Additional posts will be necessary to cover the air barrier. 

     

    Requirements in the building code for air barriers began to evolve in the early 80s as a result of the Arab Oil Embargo.  Air leakage of a building wastes the energy required for heating and cooling it.  Air Barriers were initially required only in Climate Zones 4-7 (the heating zones).  See the Climate Zone and Moisture/Dry/Marine Region map below.  It is one of the first things that I refer to when beginning a commissioning assignment.  

    Today, air barriers are required in all climate zones and regions with one exception.  Air Barriers are not required in the counties in southwest Texas along the Rio Grande river, in Climate Zone 2, Dry (B) Region. 

    There is a progression of performance requirements for air barriers: the materials, assemblies, and the whole building.  The allowable air barrier air leakage rates are:

    • Materials must not exceed 0.004 cubic feet per minute per square foot (cfm/sq.ft.) at a pressure differential of 0.3 inches water gauge (w.g.). (also expressed as 1.57 lb. per sq. ft (psf) or 75 Pascals (Pa))  Testing is in accordance with ASTM E 2178.  
    • Assemblies of materials and components must not exceed 0.04 cfm/sq. ft. at a pressure differential of 0.3 inches w.g. when tested in accordance with ASTM E 1677.
    • Whole building air leakage must not exceed 0.4 cfm/sq. ft. at a pressure differential of 0.3 inches w.g when tested in accordance with ASTM E 1827 or ASTM E 779.

    NOTE: The building code specifies the E 779 test, but E 1827 is a more effective test because it can test the building with both positive and negative pressures, and uses "blower door fans". 

    What does all of this mean?  And how is air leakage rate of a building actually determined?  Also, be aware that the air leakage rate of materials is based on the air leakage of gypsum board.  There are several common construction materials that are listed in the building code as air barrier materials.  I like to separate air barriers into two groups: Air Barrier Materials and Air Barrier Products. 

    Air barrier products are promoted by the Air Barrier Association of American (ABAA).  I was an "Auditor" for ABAA for two years, and quit because it was a complete waste of time and effort for verifying building air leakage, and completely wasted money for the owners.  The test methods of the audit are not effective in verifying building air leakage. 

    I have been tasked with determining the air leakage of numerous buildings that have included many single-story free standing branch bank buildings, U. S. Army Corps of Engineers (USACE) buildings that included a single space building with a 1 million cubic feet volume, as well as a high rise apartment building.  I have yet to have a building to pass the air leakage E 1827 test.  For the high rise apartment building, a single apartment was tested.  When the required air pressure could not be achieved, smoke was used to identify leak locations, which was mainly at the floor to facade curtain-wall joint. The smoke traveled into the apartments above and below; a code violation.  To my knowledge nothing was done to correct the condition. 

    I have presented my program on Building Envelope Commissioning for the USACE, and always ask how often they get a building to pass and, the answer has always been, "only very small ones".  

    To Be Continued



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    George Blackburn [AIA]
    Blackburn Architecture
    [Carrollton] [Texas]
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  • 2.  RE: Building Envelope Air Barriers

    Posted 04-28-2020 12:36
    George, I enjoyed your dissertation on air barriers in curtain walls. I found the inclusion of the Climate Map very informative. I have 1(one) request-can you provide your recommended curtain wall detail showing the proper application of the air barrier? Much appreciated TakeCare, Mark C Miller

    Sent from my iPhone