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ZIP Window Detail with Exterior Insulation

user-6603947 | Posted in Green Building Techniques on

On ZIP’s website, they have window details which appear to combine the flashing/window buck of an outie window, but it is shown flashing into a WRB (in this case the ZIP sheathing) located behind the exterior insulation.

Is there any reason this method cannot be employed with dealing with standard OSB and house wrap? I am planning a deep retrofit on our current home, and I would rather leave the WRB at the sheating, but outie windows seam easier. Can I install the window buck, flash the buck back into the WRB at the sheathing, then install my exterior insulation (in my case, Roxul Comfortboard due to the presence of poly on the interior of the wall.

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  1. DanCK | | #1

    Hello Derrick,
    I'm planning a similar setup when I build later this year with flanged windows and comfortboard on the exterior. If you look at the Comfortboard installation manual, they do flash the buck back to the WRB on the sheathing when using flanged windows.
    I was planning on vinyl siding and flanged windows that have an open J- brickmould to accept the end of the siding so the simplest install for me is to have the windows and WRB on the same plane. I did speak to a Roxul rep and their reply was:

    Placement of the air/weather barrier membrane directly against the exterior sheathing, before installing the COMFORTBOARD™ is to provide air sealing / weather protection of that sheathing.

    Placement of the air/weather barrier on the opposite side is doable but harder to detail, and less durable because the COMFORTBOARD™ will also provide protection of the barrier.

  2. user-6603947 | | #3

    Thanks for the resources. On a somewhat related note, how superior is it to install windows with a nailing flange that can be taped/flashed as opposed to interior anchors with no nailing flange. Adding exterior insulation was going to be cost-effective because I thought insurance was going to pay for replacement of our siding to accommodate new windows (old windows were damaged by hail). I heard back from them today, and it sounds like they have changed their tune. They may still pay for partial siding removal, but they aren't going to cover the whole house.

    That being said, we likely will not be able to afford the cost of new siding & rigid insulation on our own, so it looks like we may just be getting new windows. I used to be a roofer and personally prefer the idea of flashing a nailing flange and relying on gravity to keep water out of the house. However, there are obviously a lot of replacement windows installed using strap anchors and polyurethane caulk. I just don't like the idea of relying on the caulk to keep water out of my walls. Any opinions on this?

  3. STEPHEN SHEEHY | | #4

    Derrick: You might find a good flashing tape more effective than caulk. 3M 8067 or Siga tapes work well. Spray foam any gaps, then tape inside and outside.

  4. Chaubenee | | #5

    I am a huge fan of 3M 8067 All Weather Tape! I like a nailing flange if I cam get it, as well. I always feel they are secured better, and are sealed tighter to the rough openings. Just my instincts.

  5. user-6603947 | | #6

    Thanks for all the replies and insight. I spoke with our contractor regarding his method for flashing and sealing the windows without removal of the siding. His description basically aligns with the attached Pella instructions (he is a Pella authorized installer that we are using for our Inline windows).

    1) These instructions make sense to me, but I am admittedly a novice when it comes to windows. These are actually the best instruction I have seen thus far for installation without a nailing flange. The biggest potential problem I see is getting the tape at the jambs and sill adhered to the WRB. I don't see the tape sticking completely to the WRB when trying to wedge it under the existing J-channel. Any tips/tricks would be welcome.

    2) I will be requesting a sloped sill pan, as he said they typically flash the sill with tape but do not slope it.

    3) They use Pella's brand of foil-faced tape. The product I found online was called Pella SmartFlash. Anyone have experience with the tape? Should I request that he use a different product?

    4) They use OSI brand caulk. I see OSI offers a couple different sealants for use on windows. I will request that he use the OSI Max, as it appears to be their best product (or at least most heavily marketed). Same question, is this the best product for our application, or should we request something else?

    The contractor did say he had no problem with me helping during installation (I want to learn to install windows but figured there are probably some tricks of the trade I should see firsthand before going solo), so I should be able to ensure these details are followed.

    I still don't like the idea of relying on caulk over a nailing flange, but it looks like we are stuck unless I want to spend an extra $13K for new siding. Would it be worth it to remove and reinstall portions of the existing vinyl siding in order to use nailing fins, or are we just creating a greater chance of damaging the WRB during siding removal?

  6. JC72 | | #7

    Try YouTube . You'll find a plethora of videos showing how replacement windows are done.

  7. user-6603947 | | #8

    Anyone have experience with the Pella-brand tape or have a recommendation on the OSI caulk? I want to ensure I get these items incorporated into our installation contract before signing.

  8. Chaubenee | | #9

    We had some Pella tape on the site during my house build. One of the contractors had some. It wasn't quite as good as the 3M All Weather. . You can't go wrong with it. Honest.

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