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Community and Q&A

Installing New Doors and Windows into Existing T1-11 Siding

sunrisehomestead | Posted in General Questions on

Hey guys-

T111 siding is the bane of my existence and runs rampant around where I live.

I typically am a stickler for window and door installation and waterproofing/airtightness details.

I prefer to install/flash to an actual sheathing/WRB layer-then siding/trim overtop.

I have a couple project I am looking at with T111 and don’t really feel 100% flashing/installing directly to the T111 and nailing trim overtop. I feel like the channels in the T111 are just asking to funnel water right down into the wall and past and tape/caulk present.

I have also seen people install housewrap over the studs, then install windows directly to WRB/Studs, then install t111 overtop and cut around the windows. In order to unearth the windows and reinstall you must take off the t111.

I don’t really prefer either method but curious how ya’ll handle new doors and windows with T111 siding existing.

I also am wondering if anyone has ever taken this approach-say existing T111 is in good shape (very rare). You are going to replace windows and doors and want to improve things a bit. What if you call the existing, stable T111 the sheathing-apply a WRB overtop, then flash all windows and doors to that as if it was a sheeted, wrapped wall assembly and now put new siding overtop of that. Essentially turning the existing T111 into a sheathing layer and putting proper siding overtop of it. Anyone ever do this successfully? My worry would be sandwiching the sheathing  (t111) between two layers of WRB (the old one underneath overtop the framing and the new one overtop of the t111 before siding).

I’d still worry if any water got in the wall (I usually use a rain screen assembly) the T111 channels could funnel water down past the flashing tape and into the wall.

Any two cents would be helpful! I have tried to crack this in my mind for awhile now and figured I’d ask here.


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  1. user-2310254 | | #1

    Is the T1-11 is good shape? If so and you are planning to add house wrap, it should be fine (at least that seems to be the consensus of various posters on other sites). If it were my house, I'd also think about adding furring strips to facilitate drying.

    1. Expert Member
      MALCOLM TAYLOR | | #2


      I second Steve's advice. I don't see a problem with treating the existing T1-11 as sheathing, but adding a rain-screen cavity would yield a better more resilient wall.

      1. sunrisehomestead | | #5

        totally. I don't not rain screen! pet peeve is the t111 channels. When I flash tape my window flanges to the sheathing-at the head- I hate the idea of water trickling down those channels past my flashing tape and into the wall. Yes I can put some caulk/sealant in the channels but I don't like to rely on that.

        Maybe this is a good application for liquid flashing for my window install-liquid flash over the flanges to the t111 "sheathing" and then I can get my liquid flash up in those channels as well. WA LA !

  2. creativedestruction | | #3

    Which will last longer, the windows or the siding? I'd bet on the windows.

    My vote would be WRB on the studs, staple something 1/8" thick on them for a drainage gap (I've used window screen spline with success), flash rough openings to that then install the window, then T1-11. The flange has to get cut in the event of window replacement, and with adequate joint space on all sides this should be able to happen without damaging the flashed rough opening and without pulling the T1-11. If new siding goes directly over the T1-11 some day, no biggie; everything's still back drained and flashed. Might need some J channel or creative trim work around the window frames but it's aesthetic not water intrusion-critical.

  3. Expert Member
    BILL WICHERS | | #4

    I've had some success sealing those channels with blobs of polyurethane caulk. I've done that here a few times, as my home has T1-11 siding (which I plan to eventually completely replace with fiber cement). You have to be really careful that the caulk adheres to the entire perimeter of the channel though, since mine have small grooves which can sometimes leave small voids.

    If you end up pulling the old T1-11 down, keep in mind that it might be (and probably is) doing double duty as the structural sheathing for the exterior walls. If you pull down too much at a time, you risk the structural integrity of the wall. I would do a panel or two, then put up the new structural sheathing, then remove the next few panels, put up a few more new panels, etc. I'd replace the panels on the corners first as a minimum before taking off the rest if you have to open up larger sections of wall in one shot.

    In my own experience, T1-11 is usually starting to delaminate somewhere around the perimeter of each panel, so my preference is to just replace it when doing any significant exterior renovation work.


    1. sunrisehomestead | | #6

      Yeah totally! I always will brace the walls on interior if possible before pulling sheathing and if I can't because of finished surfaces, I just pull a handful of sheets at a time. My worst nightmare is having a building rack on me because I took too much off at once or didn't brace it. Yikes!

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