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Community and Q&A

Choosing an Air Barrier

acarbs12 | Posted in Green Products and Materials on

So we are doing a renovation and an addition. When we built in 2007, the importance of air sealing hadn’t quite made it to all builders. So we ended up with your typical 2×4 walls with r15 in the walls and tyvek on the exterior. Still seems to be the case here in Southeastern, MA with a few exceptions.

So now that we decided to stay here for the long haul and are doing a major renovation which requires removing all the siding I want to tighten up the envelope. For the new construction we are going to go with the zip system for all the sheathing details.

The real question comes with what to do on the existing house. We debate whether to use a fluid applied product such as polywall, or proseco cat5. And I think I have settled on a SA product, but there are so many I’m trying to find how to compare to choose.  My inclination is to go with the  Siga Majvest 500 SA ( and I don’t think I could go wrong there ), but I feel that might be the cadilac of products… So I’m wondering if something like Blueskin VP100 might be in the same category, or the Solitex ADHero or Solitex Mento 5000. Seems very difficult to find decent comparisons between some of these products based on performance, durability and cost, and ease of installation for someone not familar with them.

Any of your professional experience with these would be greatly appreciated

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  1. GBA Editor
    Kiley Jacques | | #1

    Read through this Q&A Spotlight and comments: Choosing an Air Barrier and a Housewrap. It has some good related information and resources BUT your question has given me a new assignment idea, as it is a good one and GBA should cover it, so thank you.

    1. acarbs12 | | #4

      Thanks Kiley I will definitely look through the resources... part of the problem I have noticed is a lot of manufacturers put forth WRB's with Air Barriers adding to the confusion.

  2. woobagoobaa | | #2

    I priced out WRBs by the sq ft a couple years ago (including Tyvek, Siga, Henry, Benjamin Obdyke, etc.). My specific needs were to water and air seal 100 yr old gapped board sheathing ... self adhered was highly recommended. I used VP100 which came in the middle of the price range with a good perm rating (relatively vapor open). I see lots of VP100 going onto old houses West of Boston.

    I was also interested in the HydroGap SA product, but it was not yet available for sale. We instead did 1/4" plywood strips outboard of the VP100 to provide air gap behind the siding.

    1. acarbs12 | | #3

      Thank you that was helpfull I have seen the Hydrogap SA, actually got some samples when I got some or the rain slicker max. What was your major determining factor on what you chose cost or some performance factor you mentioned that is was gapped boards did that limit your products i know they have specific products to deal with that.

      1. woobagoobaa | | #6

        Providing a good air and water barrier for the gapped board sheathing drove the decision for self adhered WRB. Ability to dry outward and good value were second and third. VP100 had a perm of 33 (?) and mid range cost. Used a lot in my area. Plus the local Henry rep was fantastic, visited my site a few times.

  3. Expert Member
    Akos | | #5

    I'm guessing your existing sheathing is OSB. In that case, there is no need for self adhered WRB. Strip the existing house wrap, tape the seams of the OSB with a quiality tape (ie Zip or 3M 8067) and install new house wrap. Make sure to also to air seal your sheathing to your foundation (tape or liquid flash) as this is a big air leak in most houses.

    If budget allows, now is the time to add rigid insulation. 2" polyiso doubles the R value of your wall assembly and makes it the same thickness as a 2x6 wall if that is what your addition is.

    Whichever way you go, I would install the siding over rain screen strapping. This makes a big difference in the durability of any painted siding.

    1. acarbs12 | | #7

      No it is actually plywood, was going to siga fentrim tape the siding to the foundation. And I was intending on adding 2.5-3 in of rockwool comfortboard to the exterior, debating furring vs a slicker max... and then hardie plank

      1. Expert Member
        Akos | | #8

        You need to seal the sheathing not the siding to the foundation, fentrim is a great product for this. The siding should have flashing/trim on the bottom to close up any gaps to keep critters out.

        You can't attach any siding directly through 2.5" or so of any type rigid insulation. The insulation must be strapped out.

        If you were using less rigid, you could skip the strapping but also mineral wool is free draining so you don't need any drainable wrap.

        If you are using rigid foam instead, strapping is much cheaper than slicker max. Slicker is a great product for cedar shingles over sheathing.

        1. acarbs12 | | #9

          Yes My appologies I mis-spoke I meant the taping the sheathing.

          I think I have settled in on some more details for folks that might be interested.

          I think I am going to go with the Harvey VP100, largely because it seems to be a solid product, cost effective, and easily available... Our local lumber yard caries it.

          I think I am leaning towards the 2.5" ( as recommended for our area by manufacturer ) of Rockwool Comfortboard 80. And as I have been researching more it makes sense to use furring strips screwed through to the studs so I have a solid base for my siding ( versetta stone / hardie plank ). I will corravent SV-5 on top and bottom according to detail.

  4. Expert Member
    Joshua Salinger | | #10

    It sounds like you have landed on a great assembly. A minor note and a personal anecdote, we used the Henry project on a colder wet day and had issues with adhesion. We switched to the Siga SA 500 after that and haven't had any issues. That being said, the Siga does cost more and if you are installing on a dry warm day you are probably fine. My feeling is the adhesive is better on the Siga product, but once the exsulation and strapping is on it should be just fine

    1. acarbs12 | | #13

      Thanks for the Heads up on this one, ya Siga 500 seems to be a premium product but given the fact that I'm doing this in the summer months, hopefully shouldn't be an issue...

      I will definitely come back and post some details as the project goes along...

  5. Expert Member
    Akos | | #11

    One thing that really helps with most peel and stick air barrier membranes is they can be installed in vertical strips with the same overlap requirement as horizontal install.

    Installing in vertical orientation is way easier. Cut to height and staple to the top of the wall, peel back the release film and adhere it as you work your way down the wall. Can be even be done on a ladder, no scaffolding needed. Quick and easy, less wrinkling and less chance of it sticking to itself.

    1. acarbs12 | | #12

      Actually this is great to think about... because this will definitely ease the installation... especially as we have to deal with weather tightness as we go replacing/installing windows.

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