Calculate roof decking with incredible precision with this free app. Based on the knowledge of the roof pitch and the length of one known side.
Works with any pitch or combination of pitches on 4′ x 8′ sheets of plywood. You should have at least some experience with decking roofs before going any further. There are two distinct traditional methods.
The most basic is simply to lay the decking to hang over the hip and then pop a line on it according to its position on the hip. Then saw it as carefully as possible as this can be extremely risky. The sawdust generated will collect on your walking surface and can make traction virtually zero.
The other way is to measure the length for the top and measure the length for the bottom. There is always one side that can be readily measured, but the other side has to ne determined by a straightedge of some sort.
Calculate the rise for rafters with any run and any pitch using feet and inches, inches or just a decimal value with ease and precision for free.
It is often necessary to establish the the rise for a particular run and roof pitch. This is so important for ridge posts and knee walls. Build your skills with this technique so this task will become second nature.
This dimension is the distance from the outside of the wall to the outside of wall where the HAP stops. This could be either the outside of the wall plate, or the outside of the wall sheathing (wherever the birds mouth hooks). This measurement does not need to include the overhang as this is done separately.
Pitch
This value is easily found on the blueprints by finding whatever corresponding view relates to the rafters. This value is always represented in mid-air right above the roof plane with a half of rectangle where the horizontal value (Run) is 12″ and the number you are looking for is the vertical measurement (Rise). The larger the pitch, the steeper the roof.
Ridge thickness
Most situations will be simply inch and a half. With the advent of more advanced building materials such as laminated beams and more complex engineering such as three ply ridges, this is not always the case. The thicker the ridge, the shorter the rafter.
Open app
Click on the Menu button
Select rafter
Click on rafter, the second one down.
Roof width
Use feet and inches then click equals.
Pitch
Enter a value for the inches per foot rise, then click equals.
Ridge thickness
Enter a dimension in inches or just use a decimal value, then click equals.
Results:
Rafter
From the long point at the top to the top of the HAP at the bottom, then click equals for more.
Rise
The distance from the top of the HAP to the top of the ridge. Click equals for more.
Run
The distance from the outside of the wall to the inside of the ridge.
My Technique
Make sure you are accurate for the three criteria you need.
Use a framing square and a sharp pencil for the layout.
Make a rafter tail from the same lumber first.
Write on the tail the length for the rafter, the rise and the run.
There are fundamental basics you should be familiar with before you should attempt to tackle a set of rafters. If you are not comfortable with the challenge, then hire somebody.
Find the pitch of any bastard pitch rafter with incredible ease and accuracy with the free Builder Fraction Calculator app.
Learn how to determine the roof pitch equivalent for any known rise and known run with the workshop below. This way you can use a framing square to get more precise cuts on rafters and other framing components.
Convert roof pitches, or any slope to degrees, faster and easier than ever before with the Builder Fraction Calculator free app.
It is useful to know how to convert slopes into degrees so you know what bevel to set your saw on for things like gable studs. Practice the workshop below to help establish a skillset where things like this will be second nature.
