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Product Guide

Membrane Air Barriers

In addition to water and vapor control, many of today's membrane products make excellent primary air barriers

Siga’s Majvest 500 SA vapor-open membrane serves here as both the water-resistive barrier (WRB) and the primary air barrier; it is not uncommon for WRBs to also function as air barriers.

Years ago, I participated in a detailed study on air-sealing techniques at the NAHB Research Center, now known as the Home Innovations Research Labs. The study demonstrated that traditional methods, like using a caulking gun and foam sealant, were effective and cost-efficient. However, the landscape of air-sealing has evolved significantly, particularly with new building regulations that include mandatory blower-door testing for homes. To adapt, manufacturers have been developing innovative products to simplify this painstaking task for builders.

One of the most notable advancements is the introduction of membrane barriers. Although they can be detailed as interior air barriers, building science experts like Allison Bailes favor putting air barrier membranes at the exterior. In his book, A House Needs to Breathe… Or Does It?, Bailes writes that exterior air barriers “solve most of the problems associated with air leakage.”

Performance-based code guidance

The applicable building codes—IECC and IRC—offer limited guidance on installing an air barrier. The codes require a continuous air barrier installed in a building’s envelope without specifying how. The air barrier must be sealed at any joints or breaks, and air-permeable insulation cannot be used as a sealing material. There are a handful of provisions, such as where air barriers should go on a wall, including the junctions between the foundation and sill plate, the top of exterior walls, windows and doors, and knee walls—and that’s it.

So, unlike other prescriptive sections of code that tell, in paint-by-number detail, how to build an assembly, the air-barrier provisions are based on performance: “The maximum air leakage rate for any building or dwelling unit under any compliance path shall not exceed 5.0 air changes per hour.”

How you get there is up to you. However, standards exist that can help you choose materials that will do the…

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  1. charlie_sullivan | | #1

    Although it's not clear in the beginning, this article seems to be almost entirely about self-adhered membranes. I think that's a good idea. I think that you can expect better short and long-term air barrier performance from an adhered membrane vs. a loose one. Membranes that are stretched loose over the exterior surface, with taped seams, edges, etc. can work too, but air tightness can more easily be degraded by minor imperfections.

  2. frontrange | | #2

    Has there ever been published testing of the "self-sealing" claims of any of these membranes?

  3. freyr_design | | #3

    What a missed opportunity with naming a non permeable membrane perm-a-barrier….

  4. Tim_O | | #4

    One more option (technically 2 options)- Rothoblaas offers Traspir EVO 260 in both a vapor open and closed version. They sell direct to consumer, and ship from their warehouse in PA I believe. The quote I received on the 260 was $810 for about 780sqft roll. They offer a line of products that I would say is generally pretty similar offerings to Siga and Pro Clima at slightly lower costs.

  5. Expert Member
    Michael Maines | | #5

    I was just about to post Rothoblaas' version but I see that Tim O beat me to it. Some of the builders I work with like it because they can get it through their regular lumberyard vs. having to order from a separate company (Pro Clima, Siga.)

    1. Tim_O | | #6

      Is the quality pretty comparable? Their interior tape and interior membrane is a decent chunk cheaper than Pro Clima/Siga options.

      1. Expert Member
        Michael Maines | | #7

        As far as I can tell. I haven't installed it myself, but my builders say it's comparable to Siga or Pro Clima.

  6. DanielCurran | | #8

    One other new-ish product that hasn't been mentioned before is VaporDry SA by Benjamin Obdyke. I'm considering using it over the plywood on my new roof and haven't seen anyone give any firsthand experience with it, but from reading it seems to be comparable to Henry Blueskin VP100. Perm rating is 14 perms.

  7. Danan_S | | #9

    I used Henry Blueskin VP100 on my house. Overall installation was pretty easy, but you have to be quite careful about not letting it self-adhere, which will waste a lot of material.

    Also, it will not stick to any surface that has dry caulk on it. I installed it horizontally from bottom to top since I was single-handed on the scaffolding, but later I learned that it's a lot easier to install vertically if you have at least 2 people.

    Overall I found it to be the least expensive vapor permeable adhered membrane among the ones I researched, and it seems like according to this article that remains the case.

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