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Tyvek Retrofit on a Wall with Windows Already Installed

Seal the WRB to the wall sheathing and window flashing, and add an apron detail at the bottom
August 30, 2021

One thing I have learned while doing the ptc@home video series is the detail for installing Tyvek home wrap in a retrofit situation where the windows are already installed.

I’ve been replacing the windows in my house over the past couple of years, one at a time as I found extra money in the budget. I’m using tilt-ins that do not disrupt the interior or exterior trim. Now that I am replacing the siding, it’s time to disrupt that exterior brick molding.

After pulling off the brick mold, I saw how the old window stops were fashioned: 1x3s around the perimeter of the opening which provides a continuous surface between the window and the 1x6 sheathing.

Next, I cut off the old sill flush with the sheathing and sealed the edges of those 1x3s with Dupont flashing tape. This seals the edges of the windows to the wall sheathing and provides a continuous substrate to tape the Tyvek to.

Step by step for Tyvek retrofit:

  • Before installing that Tyvek, though, install FlexWrap flashing tape tight to the outer edge of the replacement window.
  • Because I’m adding a couple of inches of foam to the outside, I only remove one of the release sheets so that the sill flashing can extend to the outside of that styrofoam.
  • The Tyvek covers the wall, and the window is cut out. The Tyvek is cut back from the window opening so that Tyvek tape can adhere it to the flashing tape installed earlier.
  • This seals the Tyvek weather barrier to the window making a watertight seal.
  • Now I can install that exterior styrofoam and fold that sill flashing down. That makes a fully-flashed window with the outside of the foam being the drainage plane.
  • The bottom of the foam is protected by coil stock slipped behind the Tyvek and taped to the face of the styrofoam.
  • Drainvent rainscreen goes on top with its bottom flap tacked behind, also to keep the bugs out.

Now I can install BORAL’s TruExterior trim and siding and call it a day.

—Ed's note: This animation is not technically part of the ptc@home video series, but its content is derived from research for that project. I thought the animation would be a great stand-alone info-nugget for remodelers, so I made it. I hope you find it useful.

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