Cutting Common Rafters

The values on the calculator that we use for common roof framing are: Pitch, Rise, Run, and Diagonal. If you have any two of those values, the calculator will quickly figure out the rest of the right triangle—which means it will tell you everything else you need to know about a rafter.

Most of the time, the two values I have are the run of a building and a specified pitch, which is why I used these values for the example in this online tutorial:

10 Responses to “Cutting Common Rafters”

1. Jeff

Excellent video and explanations. The only downside I think is that you need to show how to do it in long hand without the calculator and be very specific. Then I think you have a complete first rate tutorial that everyone will want to see. Good job!

2. Bill Gesell

Mike,
After reviewing numerous articles and books, your tutorial on cutting common rafters is the best I have seen. I do not do 2 story garages everyday so now I am confident I can make 16:12 2×10 rafters fit…With one exception: In testing your method on a shorter board and using a Construction Master Pro all the calculations run, calculated rise, pitch, diagonal, plumb cuts/lines worked fine but when I added the HAP and deducted the 11.25″ ridge beam, my story pole was 5/16″ higher than it should be. Can you tell where I may have erred or is 5/16″ manageable? Thanks.

• Dan Hughes

I think this is where you are getting a difference. If you assembled the roof and planed the top edge of the rafters to the center of the ridge the distance from the point that the rafter planes above of the ridge measured to the top of the ridge would equal 5/16″. ( this 5/16″ measurement will change based on the slope of the roof and the thickness of the ridge). Adding the total rise to the HAP equals what we call the actual rise. Taking half the thickness of the ridge and the slope of the roof and setting these up in direct proportion to each other will figure the amount that the ridge is lower than the actual rise. If you don’t allow for this measurement the story stick will be too long.

3. Emanuel Silva

Mike,
Great video. Very easy to follow and understand.
Thanks again

4. Gigi Tirlea

Mike,
What a great video about “Cutting Jacks rafters” like this one about “Cutting Common Rafters”.
Thanks.

PS
I am in Europa, Romania, and i use a framing square in millimeters by Stanley.