Cavity closers prevent air and moisture flow by filling the space around rough openings. Made from rigid plastic and foam insulating, cavity closers are decay-resistant and increase a building's energy efficiency. They are available in various lengths and widths and can be custom made to fill irregular cavities. Also, they can be installed while building a wall section or after the section has been completed. Installing cavity closers requires basic carpentry skills and tools.
Measure the length and width of the window if you are building the wall section; measure the length and width of the window opening if the wall section is already built.
Select a cavity closer near the width of the space to be closed. Select the next largest size and trim it with the utility knife if you cannot find the exact size.
Cut the closer to fit the length and width of the opening. Drill holes every 6 inches around the closer flange, and nail the closer to the jam (vertical) and sill (horizontal), if you are building the wall section. Push the closer into the cavity, if the wall section is already framed.