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Integrating Windows with Water-Resistive Barrier

hamiltonworks | Posted in General Questions on

Hello GBA friends,
(I apologize ahead of time if this is a silly question)
For context- Climate Zone 5b.
I’m attempting to install a few flanged windows in my detached garage, which is going to be my workshop.
-The existing structure/wall assembly is: 2×4 studs 16″ O.C., heavy tar paper over the studs, then 1/2″ sheathing, then vinyl clapboard siding.
I believe the sheathing might actually be a ply T1-11 siding, that was then sided over later with the vinyl. (I need to verify)
So, how do I integrate the windows into the WRB if it’s behind the sheathing?
Do I want to attach my windows to the plane of the studs?
Could the T1-11 be considered a drainable housewrap, haha?! Therefore install and flash the windows to the plane of the sheathing?
Do I have to tear off all the siding and install a new WRB over the sheathing so I can install the windows in the plane of the sheathing and have it all integrated?
Please let me know if more information is needed.

Any help and insight would be much appreciated! Thank you all!

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  1. russellchapman | | #1

    If you apply sealant behind the nail fin on the side jambs and head (not bottom) you're pretty much there aside from the minimal amount of leakage at the bottom fin which should be left unsealed just in case moisture finds it's way down there.

    1. hamiltonworks | | #2

      Hi Russell,
      Thank you. Yes, I understand that aspect of the the installation, but my question is where (in what plane) do I attach and install the windows? My WRB is behind the sheathing attached to the studs. There is no WRB/housewrap over the ply T1-11 sheathing, therefore installing over the sheathing doesn't integrate it into a WRB. (Sorry if this isn't making sense.) I believe what you are saying though is go ahead and attach to the sheathing regardless of WRB location?

  2. Expert Member
    Josh Salinger | | #3


    It sounds like the garage was originally clad in T1-11 if I had to venture a guess. There is no real great way of installing flanged windows in this assembly and the ultimate answer would be to install a new WRB outside of the sheathing, integrate the window and then re-side. Beyond that, any solution will be a compromise (welcome to construction!) and a decision on risk tolerance. Since it is a garage, it is likely less of an issue if there is water intrusion than say, a new custom home.

    One solution/option could be to install a flangeless window. You could protect the RO with a high quality acrylic tape that could be integrated with the existing tar paper. Ideally you could pry back the sheathing and access the tar paper. At the head condition, one could tuck flashing behind it for a positive lap. The window could be stopped in with the head and jamb trim on the exterior and stopped in on all sides on the interior. A sloped bottom sill with positive drainage to the exterior would be important. Of course, the style of trim on the garage makes a difference and may make this solution trickier or easier depending on the situation.

    1. hamiltonworks | | #5

      Thank you so much for your insight and suggestions! The sheathing is in fact T1-11. I had a feeling this project was gonna be a COW (can of worms) ha. I Might end up taking the siding off and installing a new WRB, so I can sleep at night. Thanks again!

  3. Expert Member


    You face this whenever there is something like T-11 used as both sheathing and a WRB. I would do as Russell suggests but also add a peel & stick sill-pan. The weak point is the head, as there is no good way to flash it.

    1. hamiltonworks | | #6

      Thank you as well. I appreciate it. One thing to my advantage I guess is that the window head is tucked pretty high up under the eves, so it may be 'borderline ok'. I am contemplating taking the siding off and installing a new WRB for a proper job. Thanks again!

      P.S.- I think my family lives near you, they're in Sooke. My dad used to surf JR back in the 70's.

      1. Expert Member
        MALCOLM TAYLOR | | #7

        T-11 often gets windows installed right on top, just caulked in place and covered by trim. It's not great, but it might be good enough for a workshop, and would avoid a lot of work.

        If I don't know your father I bet we share a lot of friends. Some great characters among those early surfers! JR has been crazy since the pandemic. Packed with people trying to get out and enjoy some time in the waves.

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