Step 2 : Install the unit in the opening
Lift the glass block window into the opening. If the window is large, you may need a helper for this -- glass block is heavy. The windows have a one-piece vinyl frame with a built-in flange for attaching the unit to the framing. Use a level to check the window's position in the opening. If necessary, tip one corner up until it is level, then put a temporary nail through the flange into the wall framing. Use shims or small blocks of wood inserted between the window unit and the wall framing to level the window. Recheck the unit with your level, and if you're happy with its position, drive nails through the remaining slots in the mounting flange. Make sure the nails penetrate into solid wood.
Step 3 : Finish the interior
With the glass block window now permanently in place, you can finish off the interior side. Fill the gap between the new window's vinyl frame and wall framing with insulation. If you use fiberglass, don't pack it too tightly (this reduces its insulating value). If you choose an aerosol foam insulation, use a minimal-expansion type to avoid creating pressure between the glass block and the wood framing.
In some cases you can reuse the old wood casing, but most likely the new glass block window will look best if finished off with drywall installed flush with the inside edge of the window.
Step 4 : Finish the exterior
Working from the exterior, install flashing on each side of the window, then over the top of the window overlapping the side flashing. Then install flashing on the bottom of the window and tuck it under the side flashing. This will allow water to run off the top flashing over the side and bottom flashing. Depending on how much siding, if any, you had to remove, cover any bare wall surface with building paper before you replace the siding.
Step 5 : Install exterior molding
Replace the exterior molding around the window opening, and caulk between this trim and the wall siding to prevent water infiltration.
Illlustrations courtesy of Pittsburgh Corning LightWise
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