Building Rafters | How To Cut Roof Rafters

rafters Tools Required:
• Framing square
• Saw
• Tape measure

A framing square is used for more than just 90 degree cuts. The plumb cut, at the top of the rafter, and the seat or heel cut, at the bottom, have a 90 degree relationship to each other. In order to build rafters you need to know the roof pitch and the roof span (overall width of roof).

While it isn't that difficult to build rafters, the wall system supporting the roof must be level and square. It is well worth the effort to rough out the wall system to be square and level so the roof framing is simple.

Many people opt for manufactured roof trusses rather than building rafters. This is a good option for less experienced carpenters or if you want to save time and labor. All of our diy pole barn kits include engineered trusses exceeding typical permitting requirements.

Roof Pitch
This refers to the roof angle or slope. It is measured by the number of inches a roof rises vertically for each foot horizontally. So, a 7 / 12 pitch roof would rise 7" for each foot of roof.

Roof Span
Roof span is the width measurement between the outside surface of the exterior walls.

Plumb Cut
This rafter cut is at the top of the roof where the rafter contacts the ridge board.

Heel or Seat Cut
This cut on the rafter is at the bottom and is designed to sit flat on top of the exterior wall.

Building Rafters
framing square use for cutting roof rafters This picture shows the alignment for a 7 / 12 pitch cut.

To make the cut:
• Use the outside numbers or the inside numbers on the framing square (not both sides!)
• Line up the tongue of the framing square where the smaller number (7) is right on the inside edge of the board
• Angle the framing square to align the larger number (12) to the outside edge of the board
• Draw a line that intersects the two numbers for the plumb cut
plumb and heel cut • To make the heel cut on the other end of the board, simply repeat the steps above but make the cut on the long side of the framing square.

Once you have the first rafter perfect use it as a pattern for the rest of your rafter building. A little practice on a smaller scale is a good idea until you get the hang of it.

For information about the rafter birdsmouth cut, this video explains the full bearing method and the 2/3 method. A birdsmouth cut is also called the heel stand in some areas. Good information about fascia and overhang is included too.

Rafter Length Calculator

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