Building your own wood frame for a single-pane window is one way to fill a window opening without the cost of a custom double or triple thermal pane. Wooden windows can last for more than a century with proper maintenance, and the style and grace of wood grain brings classic elegance to any space. Careful measurements and handling of the glass are the key factors in making this project a success. Choose wood that complements your existing woodwork for a window that adds to your interior design.
Measure the rough opening for the window inside to inside from side to side and top to bottom. Cut pieces of 2-by-4 lumber, in your choice of grain, to fit. Cut all four sides with 45 degree mitres at each end, one right and one left, so that the outside points of the mitres are ¼ inch shorter than the inside measurement of your rough opening, using a mitre saw.
Set your table saw to ½ inch depth and the fence ½-inch from the blade. Run each piece you cut in the previous step with the narrow inside edge over this blade. The points of the mitres should be on the top edge. Flip each piece around and make a second pass with the opposite face against the fence of the table saw to create a 1/4-inch wide, 1/2-inch deep groove down the centre of the inside edge.
Run a sharp 1/4-inch wood chisel through each of these grooves to remove any slight rib that may remain in the bottom of the groove.
Purchase your glass 7/8-inch wider than the short inside edge of your horizontal mitred pieces and 7/8-inch longer than your vertical pieces, and 3/16-inch thick.
Glue and nail the horizontal pieces to one of the verticals with wood glue and finish nails. Match up the 45 degree mitres to form 90 degree corners, picture frame style.
Slide the glass into the frame from the open side. Gently work the glass all the way into the bottom of the groove. Do not force the glass. Run the chisel back through any groove that resists the glass.
Align the remaining vertical piece with the open ends of the horizontal frame pieces. Glue and nail it into place as before. Check the corners of your frame with a square and use a hammer to gently adjust it, by tapping in on the left or right top corner, while holding the bottom firmly to a stable work surface until it is square.
Cut ½-by-3/4 inch strips to fit the inside of your rough opening. You will need two top and bottom pieces and four sides. Nail one top and one bottom into the opening, flush with the outside edge, ¾ inch face against the window opening frame. Cut the two side pieces to fit vertically between these two and nail them to the sides. Run a bead of silicone caulk around the inside edge of this frame.
Place your window frame in the opening, pressing it against the "stop" frame you created in the last step. Apply a bead of silicone along one 1/2-inch edge and install the remaining 1/2-by-3/4 inch pieces against the inside of the window frame as you did the outside.