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T1-11 residing with cedar shingles

user-6414675 | Posted in General Questions on

Hello, I’m a subcontractor and homeowner in a neighborhood of late 70’s T1-11 clad ranch homes. I’m changing windows and shingling my own home and hearing from neighbors that they are interested in having similar work performed on their homes. In my case, a previous owner had beveled cedar siding put directly on the existing painted T1-11 in the early 90s. In the case of one neighbor in particular the existing exterior is painted t1-11.

When I did the side of the house most severely hit by rain I found some rot on the T1-11 and decided to rip down to studs and re-sheet in plywood, then tarpaper, with shingle siding. I was also concerned with having tar paper against the studs, then T1-11, then another layer of tar paper, then shingles.

But now that I’m on to more protected sides of the house I find the T1-11 under the bevel siding to be in good condition and I don’t want to rip it off. Rather I’m thinking I will keep it, add a layer of #15 tarpaper, and shingle. Is there cause for concern having T1-11 sandwiched between tar paper? And does it justify ripping everything off on a historically dry side of a house? Would it be better to shingle directly to the T1-11 same as the crew before when they added bevel siding in the 90s?  

My thinking is that painted T1-11 can’t be that different from the new zip system sheeting. Ha, anyway, sorry for such a winded question. Finally, on homes with the original T1-11, can one in good conscious (assuming the plywood is solid) reside directly on top (seemes to have worked fine for nearly two decades at my house)? And if residing ontop of T1-11 sounds resonable, do you add a WRB (tarpaper) or not?

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Replies

  1. GBA Editor
    Brian Pontolilo | | #1

    Hi Douglas,

    It would be helpful to know where these houses are located.

    In general, if you are sure the T1-11 is sound, I can't think of any problem that an additional WRB would cause. In fact, if you'd like to make an impact on the efficiency of the homes, you could use a fully adhered WRB which would do quite a bit of air sealing. Unless you know what is going on inside the walls, make sure that the WRB is vapor permeable, which most are.

  2. Expert Member
    Dana Dorsett | | #2

    A second WRB doesn't hurt, and taping the T1-11 seams or using a fully adhered WRB can improve the overall air tightness. You'll still want to add a mesh type underlayment for the shingles as a capillary break and to promote drainage and air-drying on the back side (Obdyke Cedar Breather, etc.), which would prevent moisture from being trapped/detained next to the WRB or T1-11.

  3. user-6414675 | | #3

    Thanks for the replies, not only because you both said what I was hoping to hear. For anyone reading this thread for changing windows installed beneath T1-11 siding/sheating I've now done the tear down to studs approach and the run your circular saw around the window set at T1-11 depth approach. With the later, you cut out the T1-11 so the flange is exposed. Given that there should be two studs running up both sides of the window you can still nail off the remaining T1-11 as well as the strips of matching thickness plywood you add to replace the cutout T1-11. I prefer keeping the T1-11 on the house as much as possible: Less work, less landfill, less material to buy.
    But, it's great to have matching thickness sheets of plywood on hand to repair any rot or areas of T1-11 that don't look like they have another 30 years of service left in them. The lower 2' of the 8' run of wall I just worked on simply was showing a lot of cracks in the paint so I pulled it off. No rot beneath but also no insulation in the bays below the window. So....it's also maybe a good thing to just get the house down to the bones. Ha, so it goes.

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