GBA Logo horizontal Facebook LinkedIn Email Pinterest Twitter X Instagram YouTube Icon Navigation Search Icon Main Search Icon Video Play Icon Plus Icon Minus Icon Picture icon Hamburger Icon Close Icon Sorted

Community and Q&A

Outie window using Roxul

user-5165847 | Posted in Green Building Techniques on

I am planning on using Roxul 3″ exterior insulation for the exterior walls, I want to install windows using the “outie” configuration and would like to have a simple method that gives me a wide nailing surface for the window flange and window trim. this is a 200 year old house that will have varying degrees of insulation(2nd floor walls will be 2×6, 1st floor walls will be 2×4). at the windows and doors I am thinking of installing picture frames made up of 2″ extruded poly with a 2×6 on the flat which would give a nice wide nailing surface while breaking up the thermal bridge. I understand the concept of vapor permeable(Roxul) and vapor non-permeable(extruded poly) exterior insulation and I am wondering if that small picture frame will cause moisture issues. Of course the picture frames will be flashed and membrane back to the WRB (sheathing), so doesn’t that in a way break up the vapor path anyways? The Roxul is great but the compressible strength doesn’t seem enough to take window/door flanges and trim. Any help would be greatly appreciated. I can email a sketch to clarify if that helps thanks

GBA Prime

Join the leading community of building science experts

Become a GBA Prime member and get instant access to the latest developments in green building, research, and reports from the field.


  1. DIYJester | | #1

    Have you checked out Roxul's installation guide? They have about 90 pages in there and the last 30 or 40 are specific instructions on how to install windows, doors, lights, spigots, etc. The details are pretty good and worth the read.

  2. GBA Editor
    Martin Holladay | | #2

    If your wall has exterior mineral wool insulation, it's a lot easier to detail innie windows than outie windows.

  3. user-5165847 | | #3

    thanks for help: The roxul installation guide is set up for "innies", due to the look we are trying to achieve we are hoping to go with "outies", plus building all those returns can be time consuming. is the method outlined problematic for moisture? are there any details for this type setup? I have seen squash blocks used with roxul also. thanks for the responses.

Log in or create an account to post an answer.


Recent Questions and Replies

  • |
  • |
  • |
  • |