Innie Window Details for Walls with Thick Exterior Insulation
Recessed into thick layers of insulation, innie windows are protected from the weather
Innie windows are windows that are installed in thick walls, flush to the inside of the wall—so the extension jambs go on the outside, not the inside. They begin like any other wall: studs and sheathing, covered with house wrap.
Step by step:
- Cut the house wrap tight to the window openings. Don’t fold it onto the framing.
- Sloping the sill directs any water that leaks in, to flow out.
- And add some flashing tape to the sill, but don’t stick the downhill leg to the house wrap — instead, adhere a wider strip to extend out past the thickness of the foam, later.
- Install jamb flashing extending into the opening as far as the window will go and out past where the exterior casing will extend.
- Install the window plumb, level, square, and centered in the opening.
- Tape the flanges, with upper pieces overlapping lower pieces, but do not tape the bottom flange.
- Fold the head flap down and tape the seams with contractor tape.
- In animation land, gravity can be suspended, but you’ll have to tuck the foam under the flap.
- If installing two layers, install them perpendicular.
- And weave the corners—outside and inside corners.
- To cover the exposed edges of the foam, make extension jambs, preassembled to the casing, and install to the window.
- If you haven’t already stuck the sill flashing to the foam, now would be a good time to do it.
- Tape the seams and corners to complete the air barrier and your sheltered innie window will be safe and dry.
—This detail is based on the jobsite best practice procedures of David Joyce, a builder in Lancaster, MA