How to Cut Rafters for a Lean-to Roof

Building a lean-to roof is a great way to add extra storage or outdoor space to your home. However, before you can start building, you'll need to know how to cut the rafters for your lean-to roof. In this guide, we'll show you step-by-step how to cut rafters for a lean-to roof.

Step 1: Measure the Length of Your Roof

The first step is to measure the length of your roof. This will determine the length of your rafters. Measure from the top of your wall plate to the outside edge of your lean-to roof. Add an extra 18 inches to this measurement to allow for overhang.

Step 2: Determine the Pitch of Your Roof

The pitch of your roof will determine the angle at which you cut your rafters. To determine the pitch, use a level and a tape measure to measure the rise and run of your roof. Divide the rise by the run, and multiply the result by 12 to get the pitch in inches. For example, if the rise is 6 inches and the run is 12 inches, the pitch is 6/12 x 12 = 6 inches.

Step 3: Calculate the Length of Your Rafters

Now that you know the length and pitch of your roof, you can calculate the length of your rafters. To do this, use the Pythagorean theorem: a² + b² = c². In this case, a is the rise, b is half the span of your roof (the distance from the centerline to the outside edge), and c is the length of your rafter. Rearranging the formula, you get c = √(a² + b²) x 2. Add an extra 18 inches to the result to allow for overhang.

Step 4: Cut the Rafters

1. Measure and mark the length of the rafter on a piece of lumber using a measuring tape and a  pencil.
2.  Use a circular saw or handsaw to make the cut along the line you just marked.
3.  To create the birds-mouth notch, measure and mark a distance of 3 inches from the bottom of the rafter on the same end as the rafter tail.
4.  Use a speed square to draw a line from the top of the rafter to the mark you just made.
5.  Use a circular saw or handsaw to make the cut along the line you just marked.
6.  Repeat this process for all of the rafters.
   

Step 5: Install the Rafters

Once you've cut all of your rafters, it's time to install them. Start by attaching the first rafter to the wall plate, using nails or screws. Use a level to make sure it's straight, and then attach the remaining rafters at equal intervals, usually 16-24 inches apart. Make sure they're all level and spaced evenly before moving on.  detail as below:

1.  Install the first rafter by attaching it to the ledger board with screws. Make sure it is plumb (i.e., straight up and down) before securing it in place.
2.  Install subsequent rafters at a spacing of 24 inches on center, using a framing square to make sure they are square with the ledger board and each other.
3.  Nail or screw the rafters to the top plate of the garage wall using hurricane ties or other hardware as needed.
4.  Once all of the rafters are installed, you can proceed to install the roofing material of your choice.
   

There you have it – a step-by-step guide on how to cut rafters for a lean-to roof. With a little patience and some basic tools, you can easily build a lean-to roof that will provide you with extra storage or outdoor space for years to come.