How to Frame a Window Sill

Framing a window is easy once you know how.

Framing for windows is a fairly simple procedure. The frame will consist of two king studs that run the full height of the wall, a sill and header that frame the opening horizontally at the top and bottom. Support framing for these pieces, known as cripples and the inside vertical pieces that form the sides of the opening, known as jack studs. Measuring and cutting these pieces to the correct dimensions is key in creating a square, plumb, stable sill for window installation.

Things You'll Need

• Utility knife
• Three-pound hammer
• 2-by-4 lumber
• 16-penny framing nails
• Framing hammer
• Tape measure
• Circular saw
• Level

Instructions

1. Measure the back of your window, without trim from outside to outside width wise and from top to bottom. Cut the drywall from the wall from floor to ceiling 10 inches wider than the opening dimensions called for by your window with a utility knife. The opening is typically a quarter inch wider than the window.

2. Remove any framing members inside this area with a three-pound hammer. Cut two 2-by-4s to length to fit between the top and bottom plates, or horizontal framing members, of the wall. These are your king studs.

3. Position the first king stud so that its outside is 3 1/4 inches left of the intended left side of the window opening. Use a level to adjust the stud left to right and make the top and bottom ends flush with the top and bottom plates of the wall. Attach the stud by toe nailing it to the top and bottom plates. To toe nail, drive 16-penny nails through the end of the stud into the top or bottom plate. Use two nails at each end of the stud.

4. Measure from the first king stud to a position 3¼ inches wider than your required window opening. Mark the top and bottom plates at this point. Position the remaining king stud with its inside face against these marks and toe nail it in place.

5. Cut two four 2-by-4's to length 1¾ inches shorter than your bottom frame sill will set. Nail one of them against each king stud, with their bottom ends on top of the bottom plate of the wall. These are your bottom cripples. Cut two 2-by-4s to fit horizontally between the king studs. These are your sill and header.

6. Place the sill flat on top of the two cripples you nailed to the king studs and nail through it into the ends of the cripples. Position the two remaining cripples between the bottom of the sill board and the bottom plate of the wall. Space them evenly and toe nail in place.

7. Cut four more cripples 1½ inches shorter than the distance from the bottom of the top plate to the inside of the header. Nail one of these against each king stud with its top end against the top plate of the wall. Position the header flat against these two cripples and nail in place, as you did the sill. Install the remaining cripples above the header as for the sill.

8. Measure the distance from inside to inside of the sill and header. Cut two 2-by-4s to fit this space. Nail them against the king studs to finish your rough window opening, complete with sill frame.

References

• "Rough Framing Carpentry"; Mark Currie; Craftsman Book, 1993
• Wayne of the Woods: How to Frame a Window