An air barrier is a material or system of materials designed to reduce uncontrolled air leakage and air infiltration through a building's thermal envelope. Remember that the thermal envelope separates conditioned space and outdoor air. An air barrier can technically be comprised of different types of material and/or coatings, such as polyolefin.
When an air barrier is assembled with a number of materials, then it becomes an air barrier system. As the Air Barrier Association of America (ABAA) notes, an air barrier “system essentially “wraps” the building shell and ensures that it protects the building from the effects of air leakage.” Air barrier systems provide a barrier to not only water vapor, but also to “pollutants entering either the building or the building enclosure, such as suspended particulates, dust, insects, smells, etc.”
The image to the right is a good example of an air barrier system. The green material is the actual air barrier, which, in this case, is made up of a cross-woven non-perforated building wrap with a breathable polyolefin coating. As you can see, the air barrier is part of a double layer High-R Liner System (Ls), which includes liner system components (fabric, banding) and two layers of fiberglass, with the air barrier laminated to the second layer of fiberglass.
An air barrier can be placed on the interior side, exterior side, somewhere within assemblies composing the envelope, or any combination thereof. In the picture above, the air barrier is placed within the assembly, which adds a lot of value to the overall system, and the building itself. When placed within the assembly, the air barrier is protected from damage by trade workers who cannot poke holes in it as they might in exposed vapor retarders. This means that the system provides a fully sealed airtight envelope.
First, a building designer must identify the air barrier. A vapor retarder can be designated as both an air barrier and as a vapor retarder. If a designer chooses to use an air barrier separate from the vapor retarder, the air barrier then cannot be a vapor retarder and must be a breathable barrier. In essence, the air barrier design needs to be amped up a notch to go further than a vapor retarder if it’s appropriated separately. If the air barrier is placed within the thermal envelope, the perm rating should be between 15 and 25 perms. This allows water vapor, a gas, to carry its moisture through the air barrier and not trap moisture. A true vapor retarder should be between .09 and .02 perms.
Both IECC 2015 and ASHRAE 90.1.2013 now require buildings to have an air barrier in the thermal envelope, and to be indicated in drawings. The first mention of air barriers was actually in IECC 2009. From then on, the next few code cycles made air barriers mandatory requirements. The air barrier is also a checklist item on a COMcheck™ report. However, remember that blower door testing is not required unless the building designer chooses to do so. Blower door testing is a compliance option that tests air leakage of the entire building as a whole.
MaxTight™ is our patented new air barrier system for metal buildings. It’s compatible with a variety of different insulation applications, including the most commonly prescribed in code compliance, High-R Liner System (Ls) applications. You can see from the picture to the left, as well as the one from earlier in this post, that MaxTight™ consists of a vapor barrier, at least one layer of fiberglass (in the pictures, two layers), and a continuous air barrier. The air barrier material is the green film in each picture.
I mentioned this before, but I can’t reiterate it enough: The major value-add of this system is the placement of the air barrier within the assembly. Remember that air barriers can be placed on the interior side, but this leaves them susceptible to damage from trade workers (Think: electricians, HVAC guys). Placement within the assembly ensures a fully sealed airtight envelope, plus reduced air leakage and air infiltration rates and much more.
Check out this page to take a look at roof and wall application diagrams. If you have questions about MaxTight™ or want more information, call your local Therm-All rep or dial 888-2-INSUL-8 for the nearest office.
In sum, as the future of code cycles change, the air barrier requirement will only increase in terms of required performance. This is a good thing for the metal building industry, as new requirements propel new innovations.
If you have questions about any of the information I went over in this post, fill out the form on this page and I’ll get back to you directly.
*Note: All air barrier system images used throughout this post are pictures of MaxTight™.
Want to make sure you don’t miss out on the latest energy code updates? Subscribe to our energy code newsletter to get blog posts sent directly to your inbox.