14 January

Top five questions answered about Air and Vapor Barriers


Constructive Barriers

By Mike Nasso, CDT, LEED AP – Air and Vapor Barrier Product Manager 

No doubt a teacher in your past has said to the class, “no question is a bad question.” He or she was probably saying that to prevent students from asking a question because they were afraid their classmates would laugh at them.

This happens in business as well. I know, because I sit near our technical support team. On the road, I’m asked the same questions as well.  Trust me, we don’t laugh. These are fundamental questions and a wrong answer can mean the difference between a pass or fail when installing an Air & Vapor Barrier. The following are the top five questions – and answers – about Air & Vapor Barriers.

1.      When using a rubberized asphalt based air barrier (fluid applied or peel & stick) on a window frame, can I use a silicone sealant?

Typically, no.  The plasticizers in the sealant have a tendency to break down the rubberized asphalt in the air barrier. This causes the asphalt to soften and the oils to leech out. The result is an ugly stain on your newly installed sealant.  The better option?  Use some type of membrane that doesn’t contain asphalt such as a butyl self-adhered flashing or a non-asphaltic fluid applied air barrier.

2.      What happens if I damage a sheet applied air barrier?

Good news. The fix is fairly easy. First, cut out and remove the affected piece of membrane.  Next, depending on the condition of the substrate, reapply primer to the area being repaired to ensure that the new piece of membrane adheres well.  After the primer has dried according to the manufacturer’s instructions, apply a new piece of membrane to the area.  Typically, an area that overlaps the affected area by 6” is sufficient.  Press the new membrane into place with a silicone roller and apply a liquid membrane product to all seams to ensure that the patch is not only water tight, but air tight as well.

3.      Can I use a self-adhered sheet applied air barrier on the roof?

While technically most self-adhered roof underlayments are air barriers, using the same air barrier that is used for walls is not safe for use on roofs.  Wall membranes act in the same way as roof underlayments by protecting against detrimental air, water, and vapor from damaging the building. The danger is that wall underlayments don’t have skid resistance to keep the roofer from slipping.  Smarter folks than me have worked long hard hours in labs to develop the right product for the right job. I take their word for it when the say use the right product for the right job.

4.  How long can fluid applied and sheet applied air barriers be exposed to UV rays on my project?

While technologies have improved air barrier UV resistance, most companies require that the membranes not be exposed for long periods of time.  That’s because the harsh UV rays of the sun break down and degrade polyethylene carrier sheets of both sheet applied membranes and unprotected fluid applied membranes.  Typically, you are safe exposing them between 30 days to 6 months. But make sure you check with the manufacturer for exact recommendations for their products.

5.      Which is better to use, a fluid applied or sheet applied air barrier?

This question doesn’t have a black or white answer.  That’s because so much depends on project variables:   How experienced are your installers?  Is your project located in an urban or outlying area?  What type of façade are you using? What time of year is it?

There are many times when an installer doesn’t have a crew used to working with a fluid applied barrier and is more comfortable with installing a sheet applied membrane.  While working in dense urban areas, spraying a fluid applied barrier may mean that you unfortunately have to pay for the car washes of all the cars in the neighboring parking garage.  Finally, if you’re working in the dead of winter in Duluth, Minnesota, then using a fluid applied membrane that can only be applied down to 20 degrees F just won’t cut it.  Like we always say, the right tool for the right job.

Testing, testing, testing

Complex new construction calls for complex new solutions. Carlisle Coatings and Waterproofing continues to be a leader in innovative products for building envelope construction.   As we develop new products, each must undergo rigorous (and costly) tests to meet comprehensive industry standards.  Recently, each of our three main Air and Vapor Barrier systems exceeded industry standards for air barrier assemblies as defined by ASTM E 2357. Take a look at our independent lab results here to find out why it’s important for you to choose ASTM E 2357 products. Here’s a hint:  ABBA now requires manufacturers to prove air barrier performance using ASTM E protocol, and increasingly, project specifications are requiring the test as part of contract requirements.

I know. White papers are boring, but this one is a quick and informative read. Plus! There’s a prize for reading it. The first person who can answer the following question will win SWAG.

Question: During ASTM E 2357 testing, what is the highest wind pressure load that CCW air barriers successfully withstood?


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