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Community and Q&A

Potential rainscreen issues…

user-1045979 | Posted in Green Building Techniques on

I’ve been interested in rainscreens for a while now but have been looking into them in more detail recently and have a couple of questions.

For context I live in Seattle and while we have (infamously) rainy weather it’s almost always drizzle, rather than driven.

I really like the look of an open-gap rainscreen, without a reglet or similar material between each panel. Is this practical, though? Is there an issue of water and/or insects getting between the panels?

I’ve also seen a lot of buildings with Tyvek (or similar) as the WRB behind the panels but I was talking to a contractor, who produces consistently quality projects, mentioned that he prefers felt since in remodels he finds that tyvek crumbles more readily than felt when opening up walls.
Is felt more reliable or are products designed specifically as a rainscreen WRB (Wrapshield, for example) actually the better product despite his concerns?

Lastly, is there an issue with the furring fasteners penetrating the WRB? Several products claim to self-cinch around penetrations but is it enough to trust the product to term effectively is there than some other component to help alleviate water infiltration?

Thanks in advance. I have been researching these questions for a while but wanted confirmation beyond marketing claims.

-Daniel Stewart
Seattle, WA

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  1. GBA Editor
    Martin Holladay | | #1

    While there were problems with Tyvek deterioration in the 1980s, the product was reformulated and most builders are satisfied with Tyvek's durability.

    There is no resolution to the asphalt felt versus Tyvek debate. If you like asphalt felt, by all means use it -- it is a quality product with a long history. If you want to read more about WRB options, see All About Water-Resistive Barriers.

    I wouldn't worry about water leakage at fastener penetrations in a WRB. The whole point of the air gap is to allow rapid drainage and rapid evaporation; that goes a long way toward solving any potential water-entry issues.

    However, the fastener penetration issue can affect air tightness, which is why I tell people that Tyvek doesn't make a great air barrier.

  2. Expert Member
    CARL SEVILLE | | #2

    If you're looking to install an open gap design, you may consider using a WRB that is UV resistant to avoid deterioration. Cosella Doerken makes a product like this, although I have not used it yet. You do run the risk of insects getting into the rainscreen space, so you may want to install screens at the gaps, but that is another layer of work and may end up collecting lots of debris.

  3. user-869687 | | #3


    I live in a building with 1/2" open joints between horizontal cedar 1x6 boards, on 2x2 vertical battens. You can poke a finger between boards to the black Vaproshield WRB. Each cedar 1x6 has a bevel cut (about 10°) down the length of the board, top and bottom. The building is about 5 years old and the siding looks fine. There haven't been any problems with water leaks due to the cladding, that I know of (but some flashing issues at openings).

    I think it would make more sense to limit the gaps between siding boards to 1/8" so there's less UV reaching the WRB. Black Vaproshield is a much better choice than Tyvek, which would be clearly visible and is not UV stable. Felt would not be any advantage for handling UV. I suspect the black Vaproshield will degrade prematurely due to the 1/2" open joints--it's just woven plastic. As for insects there are some wasps that nest behind the cladding.

    I have the idea that it would improve the system to fit 1.5" mineral wool batts between the 2x2 battens to back up 1/8" (or maybe 1/4") open joints. This would keep the WRB in the dark and the wool is UV stable. It would still allow enough air and vapor movement behind the cladding to behave as a rainscreen. This would keep the bugs out, slow the spread of a fire, and add acoustic and thermal value to the wall.

  4. user-980774 | | #4


    Won't the batts behind the cladding act like giant sponges and defeat the purpose of the air space?

  5. JWXNMHqdgg | | #5

    I have installed several open joint systems, all using Wrapshield and haven't had a callback yet for leaks. I'm pretty happy with it but there are several other options out there also meant for open joint applications. It's recommended to double up where you get UV exposure. We've only done 4x8-4x10 panels so we just run a strip behind the horizontal joints, the verticals get covered by the furring strip. You'll pay a lot more for it than felt or Tyvek but worth the piece of mind IMHO. And as TJ mentions, flashing details are crucial. We haven't ever done anything to keep bugs out, they do get in, but I wouldn't try the mineral wool, some type of screen situation would be preferable but as Carl says, lots of extra work that I haven't felt was worthwhile.

  6. Trevor_Lambert | | #6

    Just a curiosity question; does anyone know the motivation behind these spam posts? I can't figure out what possible benefit they get from them.

    1. Expert Member
      BILL WICHERS | | #7

      I suspect they’re probing to see if they can post at all, thinking if the post goes through maybe they can advertise or something like that. Or maybe some of them are just “me too” posts. I’ve see a number of these over the past week, all replying to pretty old threads. Since they seem to get removed pretty quickly, their main function right now seems to be to be a nuisance to the site admins, unfortunately.


      1. Trevor_Lambert | | #8

        They are all, or mostly, "me too" posts. But that doesn't really explain the motive. What does someone get out of being a nuisance to the site admins of a random website?

        1. GBA Editor
          Martin Holladay | | #9

          My guess: (1) They are generated by robots with a (very limited) amount of artificial intelligence, and (2) The spam software watches to see how long these test comments stay up before being deleted.

          Sites where the comments stay up without being deleted thereupon become targets for waves of revenue-generating spam.

  7. Stockwell | | #10

    Proclima makes an open joint cladding WRB that looks quite robust

  8. Expert Member
    MALCOLM TAYLOR | | #11

    Apart from fashion, is there any reason to choose an open-gap cladding?

    1. Expert Member
      Akos | | #12

      Cost of gaps is free, when putting up something like 1x3 horizontal cedar, save about 5% material for each extra 1/8" gap on an 8' wall.

      I think it is also easier to hide material and build defect with gap (plus a great way to cheat if the wall is off square)

      1. Expert Member
        MALCOLM TAYLOR | | #13

        yes but you end up with a cladding that only does half of what it should and transfers those functions to the secondary layer behind.

        1. Expert Member
          Akos | | #14

          Depending on the ratio of gap height to cladding width, not much makes water makes it through the gap. Even if some makes it through, its not going to get the WRB in a rainscreen type build(in a normal rain storm at least).

          I agree it is not as good as a proper lapped siding. It does seem silly to go out of your way to ensure the backside of the cladding can see water. It does look good though.

          My thinking, a brilliant salesman is one that can sell less of something to a costumer, charge more for it and also have the costumer think they got something extra.

          1. Expert Member
            MALCOLM TAYLOR | | #15

            As someone who studied architecture I know only too well how seductive these trends are. They are still like a bit like heroin to me and I've tried for years to break myself of the habit.

  9. BrianPontolilo | | #16

    Last year I visited a job site where the builder was installing open-gap, rain-screen cedar siding, based on an architect's design. If I remember correctly, the choice was about style, not any improvement in durability over any other type of siding installed with a proper rain-screen detail. What I thought was interesting was that because he didn't want the nails to bleed and discolor the siding (and it was a coastal setting) and because the nails would be exposed, he was using stainless steel nails and very carefully hand nailing the siding. The look is stunning, at least to me, but that's a lot of extra cost in fasteners and time, and like many of you here, it seems to invite issues (like UV degradation of the WRB, insects infiltration, etc.) that a closed systems does a better job of defending. I'll reach out to the architect on that project, and see if he has time to share some thoughts here and maybe a few photos.

  10. tedbuilds | | #17

    Here in Toronto, Canada, we are concerned with a few (new?) species of very aggressive wasps and hornets nesting in any protected volume. They routinely chase guests inside during our summer. To build an open rain screen is almost 'reckless disregard'.

    For those on the west coast, Menzies Metal of Vancouver stocks perforated bottom and top bug screens for steel sheathing and roofing, in both galvanized and aluminum.

    As a general question, perhaps it's a balance between your ethics and money. Do you build, teach or lose the job because you quote too high?

    How do you educate a building's owner that a caulked rain screen will need to be re-caulked one day, that a cheaper open rain screen invites bugs and that a closed-joint rain screen will initially cost more?

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