How to Measure For and Install Replacement Windows

Few project will more dramatically change the look of your home (and your energy bill) than installing new windows. Modern replacement windows come in self-contained, pre-hung units that are a lot easier to install than the old-fashioned wood sash windows you're replacing. It's crucial to get the proper measurements before you order the replacement windows, as they generally have to be custom-sized.

Things You'll Need

• Tape measure
• Pencil
• Paper
• Hammer
• Flat bar
• Fiberglass insulation
• Carpenter's level
• Wood shims
• Screw gun
• Mounting screws (provided with the window)
• Caulk

Instructions

1. Measure across the width of the opening with a tape measure, from the furthest points outward (generally, inside the track where the sash slides up and down). Measure across the top, bottom and middle of the space, to determine if there's any variation. If the measurements aren't the same, choose the smallest number. Write down the number. Repeat the process to measure the height of the opening. Subtract 1/2 inch from the width and height numbers, and base your window size on those adjusted numbers.

2. Remove the trim that holds in the window on the inner edge of the opening, using a hammer and flat bar. Don't break the trim as you remove it. Set it aside.

3. Pull the bottom window sash toward you, into the room, and remove it. Take out the strip of vertical trim that was between the two sashes so you can pull the upper sash out as well.

4. Lay a strip of fiberglass insulation on top of the window sill. Stand the replacement window unit on top of the insulation. Push the window unit into the opening, tucking insulation around the edges. Push until the unit rests against the trim that's around the outward-facing side of the opening.

5. Shim the on the bottom and sides of the replacement window to level it, and check the alignment with the level. Once it's level all around, use your screw gun to drive mounting screws through the screw holes on the sides, out into the side frame of the opening.

6. Reattach the interior trim with a trim nailer, trapping the new window in place. Run a bead of caulk all around the edge where the replacement window meets the trim. Caulk the exterior perimeter as well.

Tips & Warnings

• Wear goggles and gloves when removing the old windows.

References

• Ace Hardware: Installing Replacement Vinyl Windows.