How to Cut Roof Rafters Like a Professional

When it comes to construction, roofing is perhaps one of the most complicated and involved projects of all. Beyond the carpentry aspect, roofing also involves complex math, so it’s easy to feel a little intimidated by learning how to cut roof rafters.

In this guide, we’ll break down everything you’ll need to know to get you ready for the job. By the time you’re finished reading, you should feel much more confident about cutting your rafters yourself.

What You’ll Need

When it comes to how to cut roof rafters, you’ll only need a few tools to get the job done right.

  • Circular saw (other saws do the job just find too, if you don’t have a circular saw handy)
  • Workbench (or saw horses)
  • Roofing calculator
  • Framing square
  • Stair gauges
  • Safety Goggles
  • Gloves
  • Carpenter’s pencil

Step I: Doing the Math

The most critical step in cutting roof rafters is calculating the measurements for your cuts. It can seem intimidating at first, but with a roofing calculator, you can make quick work of the mathematical portion of the job.

If you don’t have a roofing calculator, this roof rafter calculator will help you accurately take your measurements. It’s also particularly easy to use, and it’s a good secondary tool to have handy, even if you have a roofing calculator.

Once you’ve crunched all your numbers, run them again, and again after that. This will help you ensure complete precision, so your final product is exactly what you were hoping for.

It’s helpful to record your different measurements for overall run, adjusted run, run, diagonal length, rise, and pitch right on the wood for the first rafter. That way, you can glance over at any time to reference your measurements.

Step II: Mapping Out Your Cuts

Once you’ve taken your measurements, you can use your stair gauges and framing square to quickly and accurately map out the different cuts for the rafter.

Chances are, you already have a framing square handy, if not, you can pick one up at your favorite hardware store, or online. The same goes for stair gauges.

While stair gauges aren’t entirely necessary for marking in your measurements, they do make the job much easier and they help to safeguard against mistakes.

The pitch of the roof will determine where you place your stair gauges. The gauge for the tongue of the framing square corresponds to the pitch while the gauge on the body corresponds to the run.

For example, if you’re working with an 8/12 pitch, your tongue gauge would be placed at 8” and your body gauge at 12”.

From there, you can map in your measurements for the head of the rafter, the length of the rafter, seat cut, fascia, and sub-fascia using your pencil.

This comprehensive guide from Irwin does a great job of illustrating how to map in these different guidelines using your framing square.

Step III: Cutting Your Template

When it comes to making your cuts, you can use any saw you have handy. I reach for a circular saw for this job, but if it’s easier for you to use a chop saw, miter saw, or a hand saw, by all means, use those instead.

Before you get to cutting, make sure that you’re working comfortably, and that you don’t have to put yourself in any awkward positions to make the cut. Be sure you’re wearing gloves and safety goggles before you reach for your saw.

Now, make your cuts along the lines you mapped out in step II. Once you’re finished, you’ll have your first rafter, and you can use it as a template to cut all of your other rafters.

Step IV: Cutting the Remaining Rafters

Use the template you completed in step III to map out the rest of the rafters you’ll need for the entire roof.

Once you’ve marked all of your rafters, you can complete all of the cuts in each rafter one after the other, which will help you to save time.

Final Word

When it comes to how to cut roof rafters, the process can feel a bit overwhelming at first. Hopefully, after reading this guide, you see how easy it is to cut rafters once you get the hang of it.

One thing that I can’t stress enough be sure that your measurements are rock solid before you mark or cut anything. The last thing you want to find out is that you cut all your rafters based on bad math, and you need to go back to the drawing board. Remember, measure twice (or three, or four!) times, and cut once.

If you’re interested in learning more about the science of roofing, and the next steps that will go into the roof once it’s framed, this guide is a good starting point.

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