Building the Sash and Sill

• 1). Measure your window opening top to bottom, side to side and inside to outside. Assume a window 24 inches high, 24 inches wide and 5½ inches deep inside to outside. Adjust the measurements to the size of your window.
  
  
• 2). Cut your sill and sash pieces from 1-by-6 and 1-by-4 inch lumber, using a circular saw. Cut two pieces at 24 inches and two pieces at 22½ inches cut from 1-by-6. These are your sill. Cut two at 22½ inches and two at 21 inches from 1-by-4. These are your sash.
  
  
• 3). Build the sill frame from the 1-by-6 inch lumber. Create a square 24 by 24 inches. Stand the lumber on edge and use glue and nails to fasten the corners. The two longer pieces will run horizontally along the top and bottom, overlapping the shorter vertical pieces at each side by ¾ inch at each corner.
  
  
• 4). Repeat the process outlined in step 3 to build the sash frame from the 1-by-4 inch lumber. The finished dimension should be 22½ by 22½ inches.
  
  

Installing The Glass

• 1). Cut eight pieces of 1-by-2-inch lumber for glass stop. Cut four at 21 inches and four at 19½ inches.
  
  
• 2). Lay the sash frame flat on a sturdy work surface. Set two of the 21-inch stop pieces in the frame--one against the top and one against the bottom, flush on the table so that they match up to the back edge of the frame. Glue and nail in place.
  
  
• 3). Set two of the 19½-inch pieces of stop inside the frame--one against the right side and one against the left. Their ends should touch the top and bottom pieces of stop to form an interior frame with an opening 18 by 18 inches.
  
  
• 4). Run a bead of siliconized glazer's caulk along the face of the inside 1-by-2 frame to stick the the glass to.
  
  
• 5). Lay the glass on top of this caulk. The glass should be cut 1/8 inch narrower and shorter than your frame.
  
  

Finishing the Window

• 1). Add the remaining 1-by-2 stop to the inside of the glass, running a bead of caulk along the face of each piece that will be touching the glass. Glue and nail in place.
  
  
• 2). Set the sill frame into the opening and nail or screw into place, and set the sash frame into the sill frame so that the front edge is 1 inch back from the lip of the sill on all four edges--top, bottom and two sides. Glue and nail in place.
  
  
• 3). Caulk all of the seams in both frames before adding casing and exterior trim to finish the window.