How to use a framing square to lay out the birds mouth cut on a rafter.
Roof pitch birdsmouth cut 2x6.
How many of us are under the 1 4 of depth or some other fraction rule by code and inspection when cutting birdsmouths in rafters.
This article series explains how to use a framing square and in companion articles we give examples just about every possible way to figure out any or all roof stair or other building framing dimensions and measurements including problems such as figuring the roof area width length and roof or stairway slope rise.
For example if you are using 6 x 2 timbers the birdsmouth should be no greater than 2 inches deep.
Height above plate table 3 12.
All roof rafters should be identical so follow the same steps to measure the plumb cut tail cut and birdsmouth cut.
Depending on the size of your structure you will need to cut several or many more.
At this point you ve cut 1 roof rafter.
The number of rafters needed will be determined by the length of your roof.
Angle overhang lay device on incline and hit start measuring to directly measure pitch.
It can be difficult to visualize rafter plumb and side cut angles and how the common hip and creeper rafters all fit together.
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.
Rick arnold frequent contributor to fine homebuilding and the journal of light construction presenter at jlc live the katz roadshow the remodeling show.
I have attached a sketch that shows how for a 2 12 rafter with full wall notch over 2 6 wallframe and 1 2 sheathing if wanting the springline from the inside edge the max pitch for the roof is 6 3 8 in 12.
If the rafter is cut for full bearing on a 2x6 wall the resulting notch would be deeper than 2 13 16 inches.
But for a 2x12 rafter on a roof with a steeper 12 12 pitch the seat cut can be no longer than 4 inches before the d 4 limitation is exceeded.
The actual indentation or cut is known as the birdsmouth while the birdsmouth plumb is the depth of the cut out.
To make it easier before you start to measure mark and cut print these templates fold over some scrap wood same size as rafters and cut through the paper to form the correct plumb and side cuts for common hip and creeper rafters.
Birdsmouth plumb if you study the diagram carefully you will see that there is an indentation in the roof rafter where it meets the exterior wall of the building.
