Are you an Innie or Outie?


Silly!  We are not talking about your belly button! We are talking about window installations of course.  Around here in the D.C. area, we do not see Innie windows very often.  In fact, I don’t think I saw any before we started thinking about the issue.  Typically, you will only see them on really old houses, I saw them at Mt. Vernon this week!  If you ask contractors or supply houses about how to do it, the most likely response is,”why would you ever do that?  We wondered about that too.

Apparently, the debate has been going on for decades among building scientists and high performance home designers.  Here’s what we are able to summarize.

Outie Windows: The glazing of the window is set flush to the outside of the wall

Outie Window

  • Easier to install: They are installed by nailing flanges on the outer face of the wall
  • Simpler drainage plane: No exterior window sill to worry about
  • Deeper interior sill: Looks nice and you can leave a cup of coffee on the sill
  • Conventional looking: Everyone has it installed this way

Innie Windows: The glazing of the window is set at middle of the wall

Innie Window

  • Greater protection from severe weather: Innie windows are removed from the outer surface of the wall which protects them from driving rain and wind
  • Better supported:  Unlike Outie windows which are basically secured by the screws on the window flanges, Innies are secured and supported by the wood frame
  • Solar shading: The recessed position of the glazing provides solar shading
  • Better thermal performance: The glazing being within the wall’s depth keeps the glazing within the insulated thermal envelope

We chose to do Innie Windows.  This means more installation steps:

1.  Starting out with over-insulation of 1″ XPS on the head and jambs.  This extra layer of foam adds R-value to the window frames.

Overinsulation

2. Wrap the rough opening with Tyvak.  The house wrap protects the home from damaging wind and rain.

Wrapping with Tyvak

Wrapping with Tyvak

3. Flash with Grace Vycor.  We use this to build a water proof head, jamb and sill.

Flash with Grace

4. Install window.  Using the expanding foam tape we previously blogged about to install the window to create an insulated, water-tight and air-tight seal around the window.

This is what our Innie looks like.

Window Installed

Window Installed 2

Windows Installed

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4 responses to this post.

  1. Here in the UK outie style windows are the type usually fitted, keeping flush to the outer wall. I have to say I didnt realise there was a debate on whether innies had better insulating properties. Will definitely look into his more, good post.

    Reply

  2. Thanks. I am glad you found it useful. The idea is that by recessing it, you put the windows to the middle of your thermal envelope instead of on the outer edge of it. By doing so, you avoid some of the exposure to weather conditions and the windows get some help from the thermal envelope.

    Reply

  3. roger, did you guys originally plan for the overinsulated frames, or was that added later? have you guys run THERM to see the benefit you’re getting?

    Reply

  4. Actually, you were the one who told me about overinsulating the window frames. When I looked at our window details, I realized our architects had actually planned it that way, I just didn’t realize. We have not run Therm on it.

    Reply

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