How to Cut Jack Rafters

Alexander Callos

Rafters are installed on the roof of homes before the plywood and shingles are added. They are long beams that form the internal framework of a roof. Rafters are available in different sizes, including from 2 inches by 4 four inches up to 2 inches by 10 inches. A jack rafter is a rafter that is part of a common rafter, but is cut and shortened for framing a hip or valley rafter. A hip or valley roof is a small roof located usually at the front of a house. Cutting a jack rafter to fit these roofs is no different than cutting any other type of lumber.

  1. Measure the length the jack rafter will need to be. Run a tape measure from the top rafter on the hip roof down to the bottom rafter and record the measurement in inches. This will be the size of the angled jack rafter.

  2. Measure the distance on the piece of lumber you will be using for the jack rafter and mark the cut location with a pencil. Slide the board into a miter saw. Press it up firmly against the fence of the saw and line up the blade with the cut mark.

  3. Pull out on the knob located on the front of the miter saw and turn the blade 45 degrees to the right. The jack rafter will always be cut at this angle so it can butt into the hip rafter.

  4. Turn on the saw and bring the blade down straight on the lumber at the cut mark. Hold the lumber firmly in place with your non-dominant hand. Cut straight through the mark and release the lever to turn off the saw. Pull out the jack rafter and carefully climb up to the roof to verify the proper size was cut.

  5. Press the jack rafter up against the hip rafter and make sure it fits properly. Repeat the process for any other jack rafters you need to have cut.