Flashing a Recessed Window

1. A bib or apron will allow the housewrap or building paper to be slipped under the window flashing later. The one shown was made from a non-adhesive fiber-reinforced flexible flashing. Extend it 6 to 12 inches past the sides of the window and staple it at the top. Do Not staple below the recess.

2. Fill the bottom recess corners with a healthy dose of sealant.

3. Embed pre-made inside and outside Corner Flashings in the sealant and staple the vertical legs. Don't staple the horizontal legs.

4. Cut along the fold of the Corner flashing where it extends past the opening, wrap the legs onto the sheathing, and staple the legs in place. Finish the Corner Flashings with pieces of folded flashing tape, as shown.

5. Install the flashing pan. The pan in the photos was made on site from 40-mil thick flashing. Two sets of hands make it easier to install the pan without wrinkles that could trap water.

6. Apply a bead of sealant at the inside corners for extra insurance.

7. Install a piece of Grade D building paper over the peel-and-stick membrane to prevent UV damage. If the house will be sided with stucco, the membrane serves as a slip sheet between the stucco and the flashing materials.

8. Install a layer of reinforced flashing (the same stuff used for the apron) from one side of the opening to the other.

9. Install vertical flashing up the sides of the opening, overlapping it past the bottom piece installed in step 8. Staple the side pieces to the face of the trimmer studs and the sides of the recess. Run the vertical flashing pieces past the bottom of the inset. Crease it into the corner and cut it with a utility knife or scissors, being careful not to cut into the preceding layers. Note that a non-adhesive product is being used in the photo. You can use a peel-and-stick flashing for this, but it can be difficult to work with and to avoid wrinkles.

10. Before installing the window, apply a heavy bead of sealant to the nailing flange, then place the window into the opening, checking the reveal from the inside. Fasten through the flange according to the window manufacturer’s instructions. Then tool sealant over the nails and over every nail hole.

11. At the top of the window, staple Corner Flash inside and outside corners in place over the vertical flashing installed in step 9. Cut along the fold, wrap the legs onto the sheathing, and stapling the legs in place.

12. Cover the top nailing fin with a final layer of flashing.

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