Window installation and Replacement Guide at The Home Depot

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.

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.

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

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 and push the brick mold or nailing fin tight against the sheathing.

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

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.

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

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.

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.

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

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

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

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.

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Window installation and Replacement Guide at The Home Depot