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How to Flash a Window Opening with Housewrap

December 25, 2015
Read time: 2 mins


Integrate the window with the house wrap, and the house wrap with the wall for an airtight, watertight window installation

Windows need to plug up a giant hole in the wall against water, air, and heat flow. And you need to be able to see through it, too. Use caulk, flashing tape, contractor tape, and smart overlapping.


The first step is cutting the window opening to make an I-cut:

  1. Cut across the top of the opening.
  2. Cut down the center.
  3. Cut across the bottom flush with the sill.
  4. Fold the sides into the opening and staple with a cap stapler.
  5. Cut off excess house wrap.
  6. Cut a head flap at the top of the opening and hold it up and out of the way with a small piece of contractor's tape.


Flash the sill

  1. Using 6-inch flexible flashing, peel the release sheet from one side of the sill flashing.
  2. Center the flashing tape in the opening and keep the back edge aligned with the sill edge,
  3. Use a J-roller to tighten down the flashing tape.
  4. From the inside of the building, flex the sill flashing out over the corner
  5. Apply pressure with the J-roller to improve adhesion.


Prep and install the window:

  1. Caulk the back of the flange sides and top (not the bottom).
  2. Insert the window in the opening, plumb and level.
  3. Use flashing tape to cover the flange, sealing the flange to the house wrap and then apply a piece of tape along the top flange.
  4. Use a J-roller to roll the tap flat.
  5. release the top flap in the house wrap and fold it over the top flange. Tape the 45 degree cuts with contractor tape.
  6. Tape across the head flap with flashing tape.

Apply low-expansion foam around the interior perimeter of the window as an air seal


—This video is from the Building America Solutions Center YouTube channel. It was produced by Building Media Incorporated with the help of DuPont.


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