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Outie window (over exulation, e.g. Zip+R) interior trim options?

oldbungalow | Posted in Green Building Techniques on

Hi if a window is installed over Zip+R (i.e. outie) how does one accommodate the extra wall thickness on the interior (i.e. the extra 1 to 2″ of thickness from the insulation) when trimming the window on the interior?

Would it be an interior jamb-extension of some sort, and is that costly (over 2 dozen windows and some exterior doors).

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  1. brianvarick | | #1

    NS Builders has videos of home making customs jamb extensions for wood Integrity windows. I’m using Integrity’s All Ultrex windows which are only 2” thick and then doing a drywall return and a wood sill.

  2. GBA Editor
    Brian Pontolilo | | #2

    Hi KT,

    Your options depend on the exact dimensions of the wall. Sometimes you can purchase extension jambs with you windows, other times they need to be made on site, in which case you'll need to get a cost estimate from your trim carpenter. That cost will have variables, like wood species, paint or stain grade, etc. Drywall returns are often a more affordable option. Like this:

  3. Expert Member


    The question assumes you are using either wood windows, or windows that come with jamb extensions already installed that will need further extending.
    Builders here typically purchase vinyl or fiberglass windows with no interior trim. That leaves us free to choose a variety of options from stain-grade wood to drywall returns. It also means the distance from the window frame to the interior wall surface makes little difference.

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