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Community and Q&A

Mechanically Fastened WRB vs. Liquid Membrane

Evan_R | Posted in General Questions on

I am a recent new homeowner. I purchased the home knowing that the stucco exterior, from ~1987, had some issues and would need to be redone over the next couple of years (worked into my negotiations). I got multiple quotes and am confident with the contractor that i chose. However, he has given me 2 options for the new system and i was hoping i could get some advice.

Basic home info:
-original structure is from 1956. An extension was placed in 1987 at which point the exterior stucco was redone. Upon investigation it seems like the person who installed it didnt not abide by the code from the 80s. There is between 5-7 inches of styrofoam behind the outer shell of stucco and there is no wrap between the styrofoam and the plywood. I have some areas concerning for rot.
-exterior surface is ~3000sqft
– i live in montreal, canada. a climate that has extremes of both cold and hot from -20C to 35C. I guess it would be considered average rainfall.

1) Tyvec system with anchors. Standard molding for doors and windows. 5 year warranty = 42000$
2) Liquid membrane system, standard moldings + flashings above all openings and at the bottom perimeter. 10 year warranty = 52000$

After reading some articles on this site it seems like the liquid membrane is clearly superior, but is it worth the cost?
is it superior as an air barrier and water barrier? Will it significantly help my energy costs? Does this system have a significantly better longevity then tyvec with anchors?

Any other advice would be greatly appreciated.

Thanks in advance

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  1. GBA Editor
    Brian Pontolilo | | #1

    Hi user-7582237 (would be great to get your name...)

    Can you describe the proposed walls in layers from the sheathing out to the stucco, please?

    1. Evan_R | | #2

      Name updated.

      The proposed system would be the Impermea system by STEF. See image attached or link below.


      1. GBA Editor
        Brian Pontolilo | | #3

        Hi Evan,

        I have no knowledge of that system, but I notice two things that you can consider.

        The first is that the layer you have options for is the water and air barrier. I would not be concerned with the Tyvek as a water barrier, but it is not a great air barrier. The fluid applied membrane will likely do much more in the way of air sealing (do you know what the specific fluid-applied product is?)

        More of a red flag is that option #1 doesn't include flashing. If that is correct, I can see why the warranty is so short.

        So, again, without knowledge of that system, I would be weary of option #1. Hopefully another GBA member with experience with this type of assembly sees your post.

        1. Evan_R | | #4

          The fluid product is

          Do you think that increase in air barrier properties has a significant enough impact on my energy costs to warrant the 10000$ extra cost of the system?

          1. GBA Editor
            Brian Pontolilo | | #5

            That would have to be modeled and there would have to be a timeframe to consider. Again, I'd be much more concerned about the flashing question.

  2. Expert Member
    Peter Engle | | #6


    Regardless of the system selected, it is important that all flashings, sealant joints, and other waterproofing details be installed in accordance with the stucco manufacturer's instructions. Most of them post their details online. In the US, most stucco systems are approved only for 4" foam because of fire safety issues. I don't see in either quote how much insulation is going back on. I've tested hundreds of stucco houses, and I can say unequivocally that more insulation is better in terms of moisture performance.

    As far as the liquid vs. Tyvek question, I am definitely in favor of liquid. I don't see any reason that a liquid membrane should cost $10k more than Tyvek. The material cost is higher and there's a bit more labor, but not that much more. When I see a big cost difference like this, it often means that the contractor doesn't have much experience with the liquid and is pricing in his learning curve. Ask some pointed questions. This might not be the contractor to do the work.

    Done properly, stucco should be a nearly airtight cladding by itself. If the Tyvek layer is taped at the seams and at the top and bottom, it should be relatively airtight itself. The foam and stucco over top will be essentially airtight, with the only air leaks at the drainage vents at the bottom of the system. For most houses, this will have little impact on overall air leakage.

    I would choose the liquid membrane, but probably not for $10k more. $1k-$2k maybe.

    1. Evan_R | | #8

      i've contacted at least 5 different stucco contractors and most gave me similar quotes, although im not 100% sure what types of systems they were using. The issue with a lot of these people was that they didnt seem to care to actually assess whether or not my property needed some repairs vs a complete redo of my siding. I ended up contacting the manufacturer STEF directly and they sent one of their experts (supposedly with 30 years of experience) to my house for an assessment. They gave me a good idea of what they thought i should do in terms of investigations and assessment to determine if repairs vs replace was the best choice. They referred me to one of their contractors who they said would do the best job and not simply "up-sell me". When meeting with him he seemed to be the most legitimate compared to the rest and seems to have lots of experience.

      - is $42k a reasonable cost for redoing a EIFS system from scratch on a 3000+ sqft exterior?
      - maybe the $10k difference isnt just because of the cost of the liquid membrane but maybe because of the other components of the system as well. unfortunately i dont know the details of the system he proposed for the tyvec option.

  3. Expert Member
    Akos | | #7

    I'm with Peter on this one, the energy saved by the liquid WRB will never pay for the $10k upcharge. Fluid applied WRB is not always superior, it is one of those that improperly done can cause issues down the road.

    For regular Tyvek install make sure there are proper flashing details around windows/doors, the EIFS manufacturer should have those and make sure the installer follows them to the T.

    If you have OSB/CDX sheating you can get most of the benefit of a fluid applied WRB by taping the seams before the house wrap goes on. This is not a lot of extra materials or labour.

  4. Cle20 | | #9


    I will do the same renovation with stucco exterior. Could you please let me know if your project went well? Thanks

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