- 1). Purchase a hopper window that is 1/2 inch smaller than the measurement for the width and height of the window opening. Obtain a measurement of the window opening by using the tape measure.
- 2). Measure the depth of the window opening and add 8 inches. Transfer the measurement to a section of roofing felt. Cut two strips of roofing felt to the height of the window opening with scissors. Cut two more strips that match the width of the window opening.
- 3). Cover the top, bottom and sides of the window opening with the roofing felt. Fold 4 inches of the felt onto the exterior surface of the wall. Secure the felt to the window opening and exterior wall with a staple gun.
- 4). Apply a bead of caulk 1 inch above the edges of the window opening. This is where the nailing fins or flange will be located.
- 5). Set the hopper window in the opening in the wall. Center the window in the opening by using a level.
- 6). Insert shims to hold the window in the opening. Drive a nail into the upper left or upper right corner of the window with a nail gun. Check the window for level. Drive a nail into the remaining corners with the nail gun.
- 7). Open and close the window to verify that it will works properly.
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