## What is the formula for cutting rafters?

Divide the adjusted width measurement by 2.

Since each individual rafter will only span half of the building’s width (minus the width of the ridge beam), divide the adjusted width measurement in half. So, the example halved width measurement will be 36.63 inches (93.0 cm).

## Can a speed square layout rafters?

Speed squares also have tables for cutting hip and valley rafters, which run diagonally at different angles than common rafters. Most rafters tend to slope from a peak to an eave on both sides of a roof.

## How do you calculate rafter length and Birdsmouth?

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 far apart are roof rafters?

But they do tend to space rafters in one of several industry-standard increments, typically either 12, 16 or 24 inches apart. These spacing intervals are measured “on center,” meaning that the measurement is taken from the center of one rafter’s horizontal surface to the center of the next rafter.

## What is a seat cut?

Definition of seat cut

: a cut at the outer end of a rafter that adapts it to fit the plate and normally has the form of a right-angled notch — compare plumb cut.

## Is 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 deep do you cut a birdsmouth?

Cutting the birdsmouth to the maximum 25% depth of a low slope (4/12 or less) rafter can cause the seat to be wider than the top plate, which weakens the rafter near the bearing point and increases the likelihood of a split.

## How do you nail a Birdsmouth rafter?

At the birds’ mouth cut of a rafter connecting to the top plate we use three nails per side, two down through the top of the birds’ mouth into the top plate and one (on either side) of the rafter’s vertical portion of the bird’s mouth cut into the face of the top plate.

## How are rafters attached to top plate?

It involves attaching the rafter to the top plate by driving nails through the rafter and into the wall cap at an angle on opposing sides of the rafter. This method is used because it simply isn’t possible to drive straight through the plate into the rafter because of the wall studs.

## How big should Birdsmouth cut be?

In a properly-cut bird’s mouth, the length of the horizontal or level line (below my two red arrows in the page top photo) should be about equal in length to the width of the top plate.

## Is toe nailing strong?

Toenailing not only makes a strong joint but also is a great way to coax stubborn boards into position. Photos 1 – 3 walk you through the basic steps of toenailing. The key to success is starting the nail in the right spot and angling it a little steeper than 45 degrees.