Air Barriers: Small Details Make Big Difference

Originally published by the following source: SBC MagazineAugust 27, 2019
by Jay Crandell, P.E. with contributions from ABTG Staff and Professional Engineers

   

In two previous articles, we explored the significance of air leakage control and the various materials and methods now available to achieve air leakage control. In this article we’ll present the two methods that work together to achieve compliance with modern energy code air leakage requirements (See Table 1 and Figure 1):

  • Air barrier installation and inspection criteria
  • Blower Door Testing

Table 1: 2009 vs. 2012/2015/2018 IECC - Residential

Climate Zone 2009 IECC 2012/2015/2019 IECC
1-2 < 7 ACH ≤ 5 ACH @ 50 pascals
3-8 < 7 ACH @ 50 pascals ≤ 3 ACH @ 50 pascals
Air sealing list & visual inspection Yes Yes
Blower Door Test Not required Required

ACH = air changes per hour; a measure of building air tightness.

Figure 1: U.S. Climate Zones

Regardless of the many air barrier materials and methods available for air barrier installation (please see “What caused the air barrier industry to develop?”), one thing is common to all of these material options. Careful detailing and sealing at joints and intersections between assemblies and components is absolutely necessary to make the air barrier material effective in end use.  Consequently, this realization has given rise to the idea of an air-barrier assembly and then, more completely, the air barrier system. The system must provide a continuous air control layer across the entire building envelope, including interfaces between all exterior components and assemblies. This means, simply put, seal all the joints, cracks, holes and penetrations (see Figure 2). 

This is a pretty simple concept, but the complexity comes in making it happen in the field with real people and a real building. These small details make a big difference in air leakage performance (like proper flashing is to the prevention of rain water intrusion). Unfortunately, it is easy to overlook or skimp on this tedious task during the frenzied nature of construction, if not effectively managed, regulated and enforced.

Figure 2:  Air barrier installation and air sealing action items

Therefore, energy codes have adopted a laundry list of air leakage sealing requirements or criteria that also serve as a means of visually inspecting an air barrier system installation. This was a major step forward. But, a visual inspection only gets you so far. Many leaks may still be missed in a visual inspection (you just can’t see the air leaks under normal conditions).

Consequently, the capstone of air leakage control has been added to the 2012/2015/2018 editions of the IECC residential energy code for homes: blower door testing. Commercial construction, however, still just has to minimally do the “laundry list” and hope the visual inspection at least finds some of the bigger leaks with no confirmation that the intended air leakage targets are indeed met and this can have significant consequences (see “What’s the Big Deal with Air Leakage?”). But, this too may (or should) change soon.

What is a blower door? How does it work? What constitutes a pass or fail? What do you do if you fail the test? Can I use it to help find leaks? All of these questions will be addressed in the final and fourth article in this series on air leakage.  

For more information on air-barriers and air-leakage control, refer to https://www.continuousinsulation.org/air-barrier

For additional information, please review the following articles and videos:

Articles

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