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Innie or outie window zone 6

cmcgrath09 | Posted in Energy Efficiency and Durability on

Zone 6 Northern NH Installing Pella Impervia triple pane casement and awning windows. After reading on this forum I planed to install them onto the sheathing then install 2in of Polyiso. (innie style) . Well Even thought last week they confirmed a August 1st delivery it is now pushed to September.  So my new plan is to install the foam and 2in PT window bucks. Then windows later. (outtie) 

Any ways is there any reason I should not go with this plan. With the window on the buck should I be worried about condensation freezing onto the window in winter? Could I get away with installing the furring strip and LP Smart siding  now and then installing windows and trim later? Doing all the work my self. With winter coming before I know it. . . 

Thank you Chris

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  1. andyfrog | | #1

    I read a blog post or interview with a builder from Alaska who said he prefers innie windows because they're subject to less wind washing and tend to stay warmer, reducing the chance of condensation.

    1. cmcgrath09 | | #4

      Yes, I also read that post/ interview and that was the reason why I was set on innie windows, but now with everything on site but the windows, I am thinking maybe just go outie.

  2. Expert Member
    Akos | | #2

    My goto budget wall is 2" exterior rigid with outie windows. WRB goes on the outside over the foam, this makes everything coplanar no flashing tape origami around rough openings.

    Outie windows are great as you have a much larger window sill, great spot for plants and house cats.

    1. Expert Member
      MALCOLM TAYLOR | | #3


      How do you handle the bucks? Similar to how Chris is suggesting?

    2. cmcgrath09 | | #5

      Do you notice any condensation on the windows? What zone do you run that set up in? Thanks

      1. Expert Member
        Akos | | #6

        The bucks are are 2x ripped to 2" face nailed onto the sheathing. The sides of the buck are sealed with tape to the sheathing which is the main air barrier. The rigid is butted right against the buck and temporarily held in place with a couple of cap nails. WRB over the foam which gets detailed the same way as a standard wall including the rough opening. The bottom of the rough opening is wrapped with flex flash over the WRB. Whole thing is strapped out with a rain screen which holds the rigid and WRB in place.

        Window from there is a standard nail fin install. I'm in the north edge of zone 5 with standard double pane windows without i89 interior coating. No issues with condensation.

        1. Expert Member
          MALCOLM TAYLOR | | #7


          Makes sense to me.

        2. cmcgrath09 | | #9

          Thank you.

        3. cmcgrath09 | | #11

          Should I slope the bucks when I rip them? I sloped my window sill 5 degrees. It wouldn't be to much of a pain to rip them at 5 degrees, but be a lot easier not to haha.

          1. Expert Member
            MALCOLM TAYLOR | | #12


            If the flanged window is going to be mounted on the bucks there is no advantage to sloping them.

        4. johngfc | | #13

          Akos - Excellent! Simple construction and exceptionally clear description. Would you have a detail drawing you're willing to share, suitable for giving to my builder? The GBA detail library seems to be virtually absent of 'modern' window detail drawings.

          1. Expert Member
            Akos | | #14

            Since I did the build myself, there is no drawing detail. The detail is somewhat non standard, I doubt you'll find a drawing for it. If you want to take a stab at sketching it up, I can help to mark it up.

      2. Expert Member
        MALCOLM TAYLOR | | #8


        If you think about the relationship of the window to the opening in a standard frame wall, and that of an outie, where isn't much difference. You could even make the case the outie was better protected by the exterior insulation against the bucks than the standard with kings and jacks next to it.

        All I can think makes it more susceptible to condensation is that it is 2" further into the RO. - which doesn't seem that significant. The big determinant of whether there will be condensation on the frame will be the Delta-T and indoor RH.

        1. cmcgrath09 | | #10

          Thank you

  3. johngfc | | #15

    Akos Comments #6 & 14 - Please see attached image. One thing I learned from this is that it's darned difficult to think about all the parts, and get them in the right places!!

    I assume the trim and perhaps sill pan need to fit the specific finish. In my case, there will be both stucco and Hardie or similar (TruExterior, SmartSide or whatever).

    1. Expert Member
      Akos | | #17

      That is pretty much it. The WRB is slit and wrapped into the bottom and sides of the rough opening. The top WRB flap laps the head flashing or window flange. This is the same as the standard rough opening detail.

      You can simplify your life a great deal by getting flanged windows with a 1.5" exterior extension (ie small brickmold or narrow sill) all around. This way the trim/siding can butt right against the window. No sill pan is needed either.

      A back dam is also simple to add. You can put a length of 1/2" backer rod or a thin piece of wood under the inside edge of the flex flashing.

      Since the WRB is outside the foam, you can also use fiber faced roofing polyiso. This tends to be the cheapest around here and is still somewhat permeable at that thickness.

    2. Expert Member
      MALCOLM TAYLOR | | #18


      If it's a flanged window (or most un-flanged ones), the portion of the frame that is outside the bucks should be sufficient to cover the strapping, cladding and part of the trim, so no flashing at the sill should be necessary. One of the main advantages of outie windows is avoiding any additional flashing or casing of the opening that is necessary with innies.

      1. johngfc | | #19

        Got it - thanks!

  4. Expert Member
    Joshua Salinger | | #16

    Hi Chris,

    One option not mentioned here is to use Thermalbuck. One of the downsides of using 2x material for the buck is that it is a thermal bridge around each window. If you go to the Thermalbuck website they have a number of different options for installs with the WRB on the inside of the exsulation, outside of the exsulation, innies, outies, etc. It is a more expensive route, but the install is simple enough and the thermal break can make a big difference with energy savings and importantly, avoiding condensation at the window perimeter (which is where most of the energy loss is on window installs). It may not be for everyone, but it's worth mentioning.

    The best way to find out the most efficient install with innies vs outies is to use an energy model. WUFI Passive does a great job, but it is a complicated model. The modeling is basically weighing the benefits accrued through shading/solar gains as the window goes further into the wall vs. the thermal benefits of placing the window in the wall (from a thermal perspective, the best place to located the window is smack in the middle of the thermal control layer). One has to weigh this information with costs, aesthetics, window type, trim details and constructibility timing.

    In general, if one is looking for solar gains, placing the window to the exterior is better. If one is looking for shading or optimizing thermal performance more towards the interior is better. With both options, a thermal break at the install is beneficial. These are rough guides, but without a complicated energy model it is a thumb in the wind kind of rule...

  5. Expert Member
    Michael Maines | | #20

    I use the sheathing as the water control layer and air control layer, and since the window performs both of those functions I like to keep them in plane when possible. I also often prefer the look of inset windows; they create shadow lines that are absent from most new homes but prevalent on older homes. The downside is having to make exterior extension jambs and sills, but they can usually be pre-assembled and if you're planning on using exterior trim anyway it may not add much if any time or cost.

    If you're set on outboard installation, I agree with Josh--ThermalBuck is made for this situation.

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