Window Installation and Replacement

Install a new window or replace a damaged one in a few simple steps

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While each window manufacturer has specific installation instructions for the wide range of shapes, styles and construction types available, on the whole, windows are installed in the same manner.

Pre-hung windows come complete with finish frames, and you can insert them in one piece into the rough opening left by the old window.

This guide will show you how to replace a damaged window or install new ones.

Tip: When performing window replacement or window repair, keep the old windows in place until you have inspected the new ones for damage and verified their size.

Safety: You can rent scaffolding to safely install windows on upper levels of your home. Because windows are difficult to handle, find someone to assist you when working above the first floor. Always wear eye and hand protection when handling glass and fiberglass insulation.

The Home Depot offers replacement window installation. Click here to schedule a free in-home consultation.

What You Need

Remove the existing window and test-fit the new one
Remove existing window test-fit  new one - Window Installation Replacement

• If replacing a damaged window, be careful to avoid jagged glass.
• Center the new window in the opening, supporting it with wood blocks and shims placed below the horizontal jambs. Make sure the window is plumb and level, and adjust the shims if necessary.

Trace around the moulding
Trace around the moulding - Window Installation Replacement

• Clamp or have a friend hold the moulding in place.
• If you have vinyl or aluminum siding, you may need to install a J-channel to hold the trim.

Cut the siding along the outline
Cut the siding along the outline - Window Installation Replacement

• Use a circular saw adjusted so the blade depth equals the thickness of the siding.
• Start the cut with the toe of the saw plate on the siding, but with the blade and heel of the plate above the surface.
• Slide the saw guard back, start the saw, and ease the blade into the wood.
• To avoid splintering, stop before the corner.
• Complete the corner cuts with a sharp chisel.

Cut the drip edge
Cut the drip edge - Window Installation Replacement

Cut a length of drip edge to fit over the top of the window, then slide it between the siding and the building paper.

Caulk around the moulding
Caulk around the moulding - Window Installation Replacement

If it has brick mold, apply a continuous bead of caulk around the opening. If it has a nailing fin, apply the caulk to the back of the fin.

Set the window into the opening
Set the window into the opening - Window Installation Replacement

Set the window into the opening and push the brick mold or nailing fin tight against the sheathing.

Level the window
Level the window - Window Installation Replacement

Check to see how much adjustment will be necessary to level and plumb the window unit.

Tack window in place
Tack window in place - Window Installation Replacement

• On a level window with brick mold, tack it in place by predrilling and then driving 16d casing nails partway into the top corners of the moulding.
• If the window is uneven, correct it by shimming below the side jambs and then tacking in place.

Use shims to fill the opening between the jambs and framing
Use shims fill opening  jambs  framing - Window Installation Replacement

Despite the nails you just put in, the window will still move somewhat. Use the shims to center the window in the opening.

Ensure correct window size
Ensure correct window size - Window Installation Replacement

• Measure the diagonals of the window.
• If they are equal, the window is square. If not, adjust the shims until the window is square. Always recheck for level and square after you adjust the shims.

Predrill holes
Predrill holes - Window Installation Replacement

• If the window has a brick mold, predrill holes in it and drive 16d nails through it and into the framing.
• If the window has a nailing fin, nail through it into the framing.
• In either case, start at the corners and space the remaining nails as recommended by the manufacturer.
• Drive all nail heads below the wood surface with a nail set.

Apply moulding over nailing fin
Apply moulding over nailing fin - Window Installation Replacement

A window with a nailing fin often has a special-order moulding that you apply over it. Install as directed by the manufacturer.

Fill with insulation
Fill with insulation - Window Installation Replacement

Fill the gaps between the window jambs and the framing members with loosely packed fiberglass insulation.

Trim the shims
Trim the shims - Window Installation Replacement

Trim the shims flush with the framing by scoring them with a utility knife and then snapping off the excess.

Apply caulk
Apply caulk - Window Installation Replacement

• Apply paintable silicone caulk around the entire window unit and fill the nail holes with caulk.
• When the caulk dries, paint to match the trim on the rest of your house.