# How do you calculate a Birdsmouth cut?

## How do you calculate a Birdsmouth cut?

Making the Seat & Heel and Tail Cut On the rafter, you want to cut, measure its overall depth, and divide it by 3. Using this figure, measure and mark two points on each side of the vertical line, which indicates where the birdsmouth will be cut.

## How can a speed square help you when your cutting?

Speed squares aren’t just for marking 90- and 45-degree angles when you’re cutting 2x4s. You can use a speed square to find roof pitches, guide your circular saw and more—including marking any angle from 0 to 90 degrees.

What is the maximum depth of a birdsmouth cut?

The cut is a ‘birdsmouth’ cut. Rafters may be birdsmouthed to a depth not exceeding one third of the rafter depth.

Is a birdsmouth cut necessary?

A lot of force is transferred down the length of the rafter, and the seat cut on the birdsmouth transfers that force directly to the top plate. In general, while the ripped-strip installation does eliminate the need to make two cuts for the birdsmouth, it’s debatable whether there are any real labor savings.

### How big should birdsmouth cut be?

When rafters are gang cut, the saw’s cutting capacity helps determine birdsmouth dimensions; a 10 1/4-inch Big Foot saw is capable of making a 3-inch seat cut, which is suitable for a wide range of roof pitches and rafter sizes.

### How do I know what angle to cut?

The formula involves dividing 360 by the number of sides to calculate the corner angle. Then divide it by two to get the miter angle. If you’re making a five-sided project with all sides equal, you divide 360 by five to get 72 degrees. So each joint or corner forms a 72-degree angle.

What is the diamond on a speed square for?

The Swanson Speed Square has a diamond cutout along the ruler that allows you to square lines and make sure they’re perfect. That diamond cutout can be used to make a notch, or a birdsmouth, for rafter work.

Do I need to cut a birdsmouth?

You need to cut them at the same angle you want your joist to sit. The beam would sit flat against the studs. However, you would need to do this in a way that it will still bear the load of weight. In addition to stud cutting, you can alternate with VPA’s.

## How deep do you cut a birdsmouth?

Before we start marking or cutting anything you have to be aware of that fact that your birdsmouth should be no more than a 1/3 (one third) the total depth of the timber you are using. For example, if you are using 6 x 2 timbers, the birdsmouth should be no greater than 2 inches deep.

## What do you use a birdsmouth cut for?

A birdsmouth cut is commonly used for a broad range of roofs, including basic gable roofs from homes, shed roofs, and other roof layouts involving rafters. The term “birdsmouth cut” may seem odd and mysterious at first, but it’s actually a fairly simple joint to make.

How is the depth of the birdsmouth cut determined?

Determine the depth of the birdsmouth cut. This is relatively simple: measure the full width of the outside wall. For most buildings, the birdsmouth cut is 4 inches (10 cm) deep: the width of the 2×4 used to frame the outer wall measures 3.75 inches (9.5 cm), and the outside sheathing measure 1⁄ 2 inch (1.3 cm).

When to use framing square for bird’s mouth?

In the sketch we show how the framing square is used to lay out the rafter length, plumb-cuts, and the bird’s mouth notch at the wall top. Make one rafter that has the bird’s mouth cut in place and extends out past that for your roof overhang, test fit it in place, and mark it PAT for pattern rafter to use in cutting its sisters.

### How do you cut a bird’s mouth on a roof?

If your bird’s mouth cut is not 4 inches (10 cm) deep, slide the framing square to shorten or lengthen the length of the cut accordingly. Measure the rafter overhang. If, for example, you want the rafter to overhang the edge of your building by 6 inches (15 cm), measure this now.