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Building Wall Assemblies: Focus on Wall Designs for Air Leakage Testing and the Role for Sealants and Adhesives

Posted on 2/27/2013 10:28:25 AM By Bob Braun
  

caulk, wall designs, air leakage testing 

In the last blog, I focused on the three common wall designs: cavity walls, barrier walls, and mass walls.  You might want to review the last blog which includes a drawing for each wall type. 

In future blogs I will review many of the test methods used to evaluate these wall types and how these standards are then becoming requirements in the model building codes.  In my much earlier Blog #3, I reviewed the many associations and groups that develop standards affecting sealants and adhesives that are used in building construction. Since ASTM methods are so commonly referenced, this society will receive most of the focus as I review wall assemblies.

Construction sealant material test methods are mostly developed in the ASTM C24 Committee.  Adhesive material test methods are developed in the committee related to the specific application for the adhesive.  For example, D08 on Roofing Standards maintains material test standards related to roofing adhesives and sealants.  In addition D08 encompasses standards for roofing assemblies as well.  ASTM D14 on Adhesives primarily maintains material test standards for a number of adhesive applications for building construction products.  ASTM E06 on Building Performance, however, is the main group developing and maintaining standards for assembly test of wall constructions.  This committee has developed test methods for wall assemblies.  In this blog, I will feature a review of ASTM E2357, an assembly test method that encompasses the use of sealants and adhesives.  This standard can be purchased online at www.astm.org .

ASTM E2357-11 Standard Test Method for Determining Air Leakage of Air Barrier Assemblies This test method covers the determination of the air leakage rate of air barrier assemblies that are used in building enclosures. This procedure measures the air leakage of representative air barrier assemblies before and after exposure to specific conditioning cycles and then assigns a rating dependent upon the results. Although this is a laboratory procedure, the method may also be used for site mock-ups.  This standard was many years in development and represents some of the latest thinking for testing wall assemblies containing various types of penetrations which often involve the use of sealants and adhesives for maintaining a good air seal.  ASTM E2357 was first published in 2005 and revised in 2011.  Today we will review this test method in detail.

Since I am focusing so much on assembly testing, please do not conclude that product material testing is not also important.  However, through testing products in combination with the many substrates and geometries they encounter in end use applications, one more clearly demonstrates performance.  Also, after the air leakage test, the assembly can be aged by simulated environmental cycling which then begins to demonstrate “durability” of all the materials used together in the assembly construction.

Now let’s review a few ASTM definitions related to air barriers:

  • air barrier—a designated “plane” of reduced air flow between different environments.
  • air barrier material—a primary element that provides a continuous barrier to the movement of air.
  • air barrier accessory—a transitional component of the air barrier that provides continuity.
  • air barrier assembly—the air barrier materials and accessories that provide a continuous designated plane to the movement of air through portions of building enclosure assemblies.
  • air barrier system—a combination of air barrier assemblies installed to provide a continuous barrier to the movement of air through building enclosures.
  • air leakage rate—the quantitative measure of air passage through a set surface area of an assembly within a given time period under a pressure differential between the two sides of the assembly.
  • building enclosure—a system of building components and materials designed and installed in such a manner as to provide a barrier between different environments, including dissimilar interior environments.

The drawing below shows the essentials of the test design and illustrates the importance of sealing penetrations with any number of sealing techniques.  Some manufacturers conducting this test may focus on the use of elastomeric joint sealants, others will utilize aerosol foam sealants, and commonly adhesive tapes and flashings are evaluated.  Also, now there are spray applied liquid sealers utilized for window flashing seals.

A Wall Assembly Specimen Design per ASTM E2357

Wall Assembly Specimen Design, ASTM, ASTM E2357, wall assembly standards

“For the air barrier system to be effective it must reduce air flow. This resistance to air flow can only be achieved by maintaining continuity (no breaks or tears). Continuity of joints must be maintained by overlapping, sealing with weatherable adhesive tapes or caulkings/gaskets. Caulked joints must accommodate dimensional changes in framing members without loss of seal integrity. Such dimensional changes can be induced by lumber drying and settling thermal movement and structural movement. Special care (for example, gasketing, sealing) must be used to reduce air leakage around unavoidable penetrations such as plumbing, air ducts, electrical conduits and window/door edges.”

Although conducting the ASTM E2357 test can be expensive, only a full assembly test can provide this wealth of data.  In addition, it can be very effective in helping the manufacturer demonstrate superior air sealing construction.  ASTM E283 protocol is used to induce pressure differences across the specimen.  Air barrier codes will determine the permissible air leakage for specific constructions based on these testing methods.  I suggest you also review again the list of the many points for air or water leakage in the building wall as I presented in the last blog.  You will see a common theme with the above drawing.                      

In Blog #23 we will look at the most common test methods for evaluating water leakage through various types of wall assemblies



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