You Can’t Buy an Air Barrier


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Professor John Straube is one of the smartest guys in building science. On top of that, I think he’s the best presenter in the field. At the Air Barrier Association conference in Baltimore earlier this year, he gave one of the best building science talks I’ve heard. Of the things he said, this statement really stood out:

“There’s no such thing as an air barrier product you can purchase. There are only air barrier systems that have to be assembled.”

The lead photo above (from my friends at Mechanical Hub) is not an example of a well-assembled air barrier system. In fact, it illustrates Professor Straube’s point. Whoever did this used several products that individually are good at stopping air leakage. A little inspection, however, shows that the system they assembled has some flaws.

There are a lot of great products out there that can help make a building airtight: structural insulated panels (SIPs); air-sealing tapes from Siga and Pro Clima; spray foam insulation;

Huber’s Zip sheathing (disclosure: they’re a client of ours); liquid-applied WRBs like Prosoco’s R-Guard and Sto’s StoGuard; and self-adhered membrane’s like Cosella-Dörken’s Delta Vent SA or Henry’s BlueSkin VP100.

But not a single air barrier product on the market can ensure you have an airtight building if you use it. Yes, you’ve got to use good products, and the more airtight you want the building, the more important that is.

Take the recessed light in the photo below as exhibit number two. It’s rated as an airtight can light. Note the gasket that’s supposed to create a nice seal between the can light housing and the ceiling drywall. When the drywall installers cut the hole beyond the gasket, the product fails. But someone who understands that an air barrier is a system, not a product, will spot that and make sure it gets fixed.

airtight-can-light-gasket-drywall

The products you use are only part of the whole system. As with most things, the devil’s in the details. You’ve got to install those products correctly. You’ve got to use the right product in the right place. And you’ve especially got to watch out for transitions and penetrations.

An air barrier is a system. Not a product.

Allison Bailes, III, PhD
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Posted In: Building Performance, Residential Buildings

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