After introducing air barriers ages ago, I wanted to talk more about their materials. I then promptly forgot about it and wrote for 8 months about insulation, heating and air conditioning. C’est la vie.
What we build our houses from has always been important. In some way or another, we need to keep the rain out and the heat in. The roof over our head has moved from caves to stone buildings that were essentially standing caves to wattle and daub to masonry construction to timber frame and, the ultimate evolution, the McMansion. Obvious from the beginning, really.
But as building science research has evolved, so has our understanding of that dividing point between inside and out. Some air barrier materials do a better job at preventing air leakage than others, but there are a number of them to choose from.
What is an Air Barrier Material?
First, what is an air barrier material…I mean besides the material from which an air barrier is made. An air barrier material is the main structural element of the air barrier. Or as the ABAA (Air Barrier Association of America…of course, there’s an Air Barrier Association) puts it, ‘provides the principal plane of air tightness through the environmental separator’. As Britta Perry would say, Super Sexy.
Much more simply put, it’s the main piece of material that makes up that wall behind you.
How can we make this conversation even more riveting? Let’s talk scientific standards! As you can imagine, air barrier materials are designed to be ‘Air Impermeable’, which sounds suspiciously like it ought to have a standard measurement. And it does.
Warning: Tech Talk!
An air impermeable material, such as one of the air barrier materials listed below (eventually), is defined as allowing less than 0.02 L/(s x m2) air permeance at 75 Pascals pressure difference across the material (That’s .02 liters of air per second per square meter).
This is tested by the ASTM (American Society for Testing and Materials), adhering to ASTM E 2178 air permeance standard.
End of Warning: Tech Talk
If the air barrier material allows for more than this minimum measurement, it is not air impermeable and is not an air barrier. Any homeowner who has had their electrician and plumber poking holes through an alleged poly plastic ‘air barrier’ sheet understands this.
Air Barrier Materials
These materials form the primary structure that (to list off the air barrier checklist) will separate interior from exterior air, provide a continuous barrier over the whole building and last a really long time. Several air barrier materials are commonly used in current construction, some familiar, other less so.
Self-Adhered Membranes – These are bituminous membranes adhered to the exterior of the building which acts as the air and vapor barrier.
Closed Cell Spray Foam – Read more about spray foam and how it acts as an air barrier in this article.
Interior Installed Drywall – The most common example in residential construction. This is drywall (or plaster in older construction) installed on the building’s interior wall.
Interior Installed Poly Plastic Sheets – Another residential standard, adding polyethylene plastic sheets to the interior of standard wall construction.
The Bottom Line
The air barrier materials are the main divider between your comfortable house and the decidedly less comfortable outdoors. Whether in a heating or cooling climate, air barrier materials help keep your house comfortable.