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Conflict between Solitex Mento and Loewen Window installation instructions

hughw | Posted in General Questions on

We’re using Solitex Mento 1000 as a WRB along with metal-clad Loewen windows with an integral flange. Installation instructions for Mento published on 475’s web site are similar to the manufacturer’s instructions with one major difference. Mento recommends that the WRB at the jambs be folded back into the jambs and the window installed over the WRB (after installation of a pan). Loewen instructions call for cutting back the WRB at the sides of the open several inches so that the window can be fastened directly to the sheathing. My gut sense is that it’s crazy to cut back the WRB and rely only on sealant behind the flange and tape, but I’m hesitant to go against the manufacturer’s instructions in case it would void the warranty. What think thee?

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  1. Expert Member


    I don't think it make much difference whether the WRB is applied before the window is installed or after as long as all the steps in sealing get covered. You can see this in the two installation instructions Dupont publishes:

    The whole question as to which instructions to follow when they contradict each other is a thorny one. Up here in much less litigious Canada, the advice my lawyer gave me was that manufacturers can not void a warranty unless the instructions that were ignored materially affected the failure of the product.

  2. CMObuilds | | #2

    Follow the windows instructions for warranty purposes.

    Folding WRB back into the jambs just doesnt make sense, since the WRB makes a imperfect air barrier it only takes a blower door test to demonstrate the amount of leakage that will come between sheathing and the WRB, a lot of people miss that folding the jamb sides in and cutting flush with the interior stud face and not sealing between the WRB and the framing. If you are folding in on all sides, give up your tools now and step away from the opening.

    I have cut WRB back so the window flange is sealed to the bare exterior sheathing, a gap of exposed sheathing and then the WRB allowing window tape to adhere to flange, sheathing and WRB and it works but its much simpler and just as effective to cut the WRB out same as the window opening, this allows the interior perimeter seal of foam around the window frame to seal the window to the framing AND sheathing/framing contact at the air barrier plane of the sheathing.

    The only weak spot where you will see possible air leakage is typically in the corners of the sill flashing whether you use flex wrap or flashing corners.

  3. hughw | | #3

    That’s pretty much what the window manufacturers instructions say to do. But I don’t love the idea of bare sheathing between the WRB and the flange and relying only on tape to seal the gap, especially in a rain screen. Perhaps lapping the WRB onto the flange, as at the head, and sealing with Tape would work best.

  4. Expert Member


    I usually install the WRB before the window. I fold it back into the jambs 1". That leaves space to air-seal the gap between the window frame and rough opening from the interior. The finished jambs then are protected by three layers: The WRB, the window flange itself, and the flashing tape.

    1. hughw | | #5

      that makes's pretty much what Mento recommends and what I would do in the absence of any other advice, but not what window company recommends which is "Cut back the Weather Resistant Barrier to a minimum of 1 1/2” exposing the sheathing at the sides only. This will create a direct contact seal between the window flange and sheathing.".....see below....But window company be dammed, I'll do it your way.

      1. Expert Member
        MALCOLM TAYLOR | | #6


        The other small thing I do when installing the rain-screen is to keep the battens off the window flanges. If you hold them back it:

        - Avoids the bulge in the battens as they pass over the flange.
        - Keeps fasteners out of the area near the rough opening .
        - Makes access to the window for repairs or replacement very easy without disrupting the WRB or flashing layers.

        1. hughw | | #7

          Agree. we were planning to keep them away

      2. CMObuilds | | #8

        With 6” or even 4” tape there’s nothing wrong with the window company detail. It will test tight.
        Rolling the WRB into the jambs at any distance is a mistake inviting 2 possible air pathways and will pretty much guarantee a pathway between the sheathing and framing to behind the WRB.

        1. Expert Member
          MALCOLM TAYLOR | | #9


          It will test tight for air-sealing, but in terms of bulk water intrusion it relies entirely on the tape, which neither Hugh and I are comfortable with.

          Whether the WRB is returned or not, the primary air-sealing at the jambs still takes place from the inside using foam and/or caulking between the window frame and the rough opening. As long as the WRB doesn't reach into where this occurs, I don't see how it causes any problems.

          1. CMObuilds | | #10

            Not if its wrapped in passed the interior edge of the sheathing, It will leak between sheathing and framing from behind WRB. Blower door proven.
            Theres still head flashing with a WRB overlap for gravity flow and you aren't going to get pressurized bulk water at an angle that will blow behind adhered window tape side jambs.

            It works, but like I said I do a cut opening same as rough, but never wrap in. Flange over WRB. Airflow from behind WRB is sealed off with the window foam fill as is any possible leakage between the sheathing/framing and window frame/framing in one step. Tests tighter and is robust against bulk water.

            So if you don't trust the tape against the sheathing what exactly are you adhering your head flashing too?

          2. Expert Member
            MALCOLM TAYLOR | | #11


            I see what you are getting at, but If the taped sheathing is your primary air-barrier, it needs to be sealed at all seams and penetrations, including windows, before we get to the whole question of the WRB and flashing. If it isn't the air-barrier, then neither the seams or edges matter.

            It's not that I don't trust tape against the sheathing, it's that I don't want the tape to be the 0nly thing protecting the sheathing where it is relied on to bridge the gap between the flange and WRB.

            At the head the opening is protected by four layers. The flange, the tape, the flashing, and the lapped WRB.

  5. CMObuilds | | #12


    Yes, sheathing is the primary barrier and edges need to be sealed. I think we agree the WRB is not an air barrier so to cover a joint that could “leak” air is akin to plugging a hole with your finger but putting a piece of plastic between the hole and your finger. The window foam or sealant needs to reach and cover the sheathing/stud seam completing the sheathing plane air barrier.

    I agree with you not trusting the tape to bridge a gap, thats why Im surprised the amount of people that rely on tape to air seal their new homes.

    No, the head isn't protected by the flange, the top flange on top of sheathing is the biggest liability to the whole assembly.

    Rolling the wrap, on the sides, doesn't hurt anything and the possible air leakage from doing so relies on multiple factors from nil to significant. All Im saying is if you want to repeatably achieve the tightest seal possible using sheathing air barrier and still have a proper drainage/flashing assembly don't roll the wrap in.

    If you want we can meet in a Walmart parking lot and square off with some mockups, sealed chamber and a duct blaster and go toe to toe on this🤷‍♂️

    1. Expert Member
      MALCOLM TAYLOR | | #14

      "If you want we can meet in a Walmart"

      Excellent idea. I need some more George brand cotton T-shirts and they are on sale this week for six bucks. See you there !

      Seriously though, I don't think we are very far apart on this - and Joe's post below shows the problems folding too far in can cause.

  6. joenorm | | #13

    This is something I have been thinking about lately.

    I followed the Tyvek instructions and folded my WRB into the jambs. But I went too far. Now I am running a razor knife along the inside of the window to cut off the excess to prep for sealing, and drywall. But I am left with WRB in-between my window RO and side of window.

    I am wondering how to remove some of it in such a tight space to be able to get a good seal between window and sheathing?

    1. Expert Member
      MALCOLM TAYLOR | | #15


      At this point probably your best bet is to use a flat drywall knife to push the WRB as far back into the gap as you can.

    2. CMObuilds | | #16

      Despite on the method I described above, I run into houses were the guys are too far ahead of me and someone has pulled the wrap in and the windows are installed.

      I trim the excess off at the window frame and as Malcolm suggests take a finish flat bar and free any staples that might be in the vicinity so its a loose flap.

      I use gun foam and I have special tips you can buy to reduce the gun barrel down to around 3/16” and I work the foam on both sides trying to encapsulate the WRB “flap” between 2 layers of foam if possible.

      As a little insurance policy I picture frame foam the stud bays around all windows at the sheathing framing joint inside the stud bays and make sure to foam wiring holes in the studs to isolate stud bays.

      Works well enough and is certainly better than not doing anything.

  7. maine_tyler | | #17

    >"Not if its wrapped in passed the interior edge of the sheathing, It will leak between sheathing and framing from behind WRB."
    > "I agree with you not trusting the tape to bridge a gap, thats why Im surprised the amount of people that rely on tape to air seal their new homes."

    So when sheathing is primary air-barrier, what are you using to seal it?
    Your concern about wrapping past the sheathing/framing joint is valid if you haven't taped or otherwise sealed the sheathing to the framing at the window rough jams, but if sheathing is being detailed for primary air-barrier, I would argue this should be done prior to window install anyway. If not, than yes you'll need the foam to make that seal and wouldn't want WRB in the way. Foam is applied through the small RO gap and is a restricted work space with poor visibility, whereas taping or sealing prior to window install is spacious and visible. Though I'm sure foaming is more than adequate with deft installers.
    Everyone has a workflow that works for them. The danger is adopting someone else's workflow/details when you don't understand why they do it that way and then mishmash systems together that don't play nice.

  8. CMObuilds | | #18

    I agree about the danger of not understanding a system or what needs to be done, the internet doesnt work well for the finer points when we all are trying to do something with various products, in various climates, under various complexities and circumstances, ect.

    I use expanding 1 component foam, I dont buy applied extension jambs and I oversize rough openings slightly so its very easy to fill. If it goes perfect I dont need the narrow tip, the gun barrel could touch the back of the flange.

    We platform frame on the floor, sheet and apply WRB and then wall jack up to 40-50’ at a time. So since the WRB is already in place Im not going to mess with sealing that seam any other way since it works for me. Like I said, I run my blower door on everything I can and I know it works.

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