Close and lock your window.
Apply your sill flashing if it is not already installed. Sill flashing is different according to each manufacturer and what the window company requires so check their requirements. The sill tape goes on the sill, up the side of the jamb about six inches and overlaps to the outside of the house on bottom and sides of the window opening. In other words, it starts on the window sill where your window sits and extends up the side where the side of your window sits and then laps over the outside of the house. You need to make sure it will extend at least two inches past your nailing flange.
Place 1/4-inch shims on each side of the window sill opening. This is where the bottom of your window will sit. The shims will be on top of your sill flashing.
Apply a bead of caulking all the way around on the nailing fin that will be up against your house, making sure you apply it over each nail fin hole. Also apply a bead all the way around the opening on the outside of the house where your window will be placed.
Place the bottom of your window on the shims in your framed opening and push the window into place.
Equal out both sides of the window. In other words if you have 1/4 inch on one side make sure you have 1/4 inch on the other side.
Nail one corner only with your 1-1/4 inch galvanized nails.
Place 1/4-inch shim on each side of the window at the bottom, one on each top corner on the side and one in the middle on each side.
Place your level on the bottom of the sill and see if it is level. If not, adjust the shims, but do not bow the window.
Place a level on one side of your window and make sure it is plumb (meaning the bubble on your level is in the center), if not adjust the shims until it is.
Measure from bottom, left-hand corner to top, left-hand corner and bottom, right corner and to top right corner. You should have the same measurements on both sides. If not, adjust your shims.
Measure diagonally from one corner to the opposite. Measure like a X. You should have the same measurements when you measure. If not, adjust your shims.
Nail in every other hole for a single window and every hole in anything bigger such as a twin.
Apply window flashing tape next to the window and across the nailing flange at least two inches outside the flange on each side. Then apply across the top overlapping the two side pieces at least two inches.
Apply window flashing tape all the way around the window on top of your nailing fin and extend it out past the flashing tape you applied underneath the nailing fin at least two inches.
Things You Will Need
- Sill flashing
- 4 or 6 inch Window flashing tape (check for brand recommend by your window manufacturer company)
- 1/4 inch wood shims
- Window caulk (check for brand recommend by your window manufacturer company)
- 1-1/4 inch galvanized roofing nails
- Tape measure
- Insulation (check for brand recommend by your window manufacturer company)
- There are many manufactures of windows so you should always check with the manufacturer for exact details of you installation. You don't want to void any warranties.