Building a wooden frame for a window can be done either in an existing wall, or when a new wall is being constructed. A wooden window frame consists of a header, studs and a sill, and it can either be added to a wall or built separately and put in place. A wooden window frame is essentially a square or rectangle box opening in which a window is going to be installed. Making a wooden window frame can be done by following a few steps, outlined here.
Use a tape measure to find the desired width and height of the window opening. Include extra space for the header and sill in the measurement.
Build a header beam. Use two 2x12 pieces of lumber and one piece of ½ inch plywood. Cut the pieces to the needed length and nail the pieces together with the plywood in the middle. A header should measure 3 ½ inches thick and 4-6 inches high when finished.
Cut a piece of 2x4 to use as the sill or bottom of the window frame. The sill should be the same width as the header beam.
Place the header beam in between two pieces of plywood that are that are the same height as the wall. Measure and cut two pieces of 2x4 lumber that are the length of the window. Place the cut pieces of lumber under the header against the longer 2x4 boards.
Place the piece of wood used for the sill under the two cut pieces of 2x4. Cut two additional pieces of 2x4 that are going to be placed under the sill. Measure the length needed from the bottom of the sill to determine how far the opening is going to be from the floor.
Nail all of the pieces of the frame together. Attach the header to the longer 2x4 pieces of lumber or studs. Nail the pieces of 2x4 under the header to the studs. Attach the sill to the studs as well as the shorter pieces that will go under the sill.
When all the pieces have been nailed together the basic window frame is complete. It should look like a box that has been attached to a stud on either side.
The window opening will be the space between the header and the sill. Use framing nails to attach the pieces of the frame together. A standard-size window can be bought off the shelf at a home improvement store.
Nail the sill from the bottom into top pieces of wood before placing the bottom pieces. If the window opening is not the exact size, trim it, or use shims to make the window fit.