How to Flash New Construction Windows
New construction windows are manufactured with integrated fastening systems. These fastening systems simplify the installation process and make a professional installation possible for even the moderately experienced do-it-youselfer. However, once the window is installed, the unit must be properly "flashed" to prevent water penetration, air leakage and energy loss.
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Things You'll Need
- Utility knife
- 3/4-inch or 1-inch wide tape measure
- Work bench or clean work surface
- Aluminum straight edge
- Roll of self-adhesive 6-inch wide window flashing
Instructions
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1
Using your tape measure, measure the width of the window unit, adding a total of 12 inches to the measured length.
Cut one length of self-adhesive window flashing to this dimension.
Apply the flashing, adhesive side toward the window and wall, along the bottom edge (sill) of the window. -
2
Apply the flashing so that the upper edge of the flashing is flush with the bottom edge of the window sill.
Apply flashing so that it covers the fastening system/device of the window and extends outward from the window, adhering to the surface of the wall.
Apply the flashing so that it extends 6 inches past the right and left edge of the window.
Essentially, the flashing overlaps the entire connection point between the window and the wall. -
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3
Repeat the process for the right and left edge of the window, also called the window jams.
The flashing should be 12 inches longer than the height of the window.
Flashing should extend 6 inches past the window sill (bottom edge) and the header (top edge).
The flashing should be applied adhesive side down toward the wall, and it should cover the fastening system, any gap between the window and the rough opening, and extend out into the wall area. -
4
Repeat the process for the the top edge of the window or the "head."
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5
When you have completed the work, all gaps between the window unit and the rough opening should be 100 percent covered and sealed with the self-adhesive window flashing.
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Tips & Warnings
The windows and doors of a home are the point at which the greatest amount of energy is lost. Proper flashing will significantly diminish energy loss and create a mechanical barrier for water, wind or insect penetration.
