## Saturday, September 8, 2012

### Unconstructable Irregular Roof Framing and My Android App

This is an example of an unconstructable irregular roof with an 135° eave angle. There aren't very many roofs in construction that have this set of angles, but I see a lot of carpenters trying to calculate roof framing angles that are unconstructable.

The common rafter pitch on the right side is an 4:12 pitched roof with roof angle of 18.43495°. The common rafter pitch on the left side was suppose to be an 8:12 pitched roof with an roof angle of 33.69007°. However, the 8:12 pitch on the right side has to be at 90° to the eave line. Which is impossible with an 135° eave angle. In order to make the 135° eave angle work with the major 4:12 roof pitch the minor roof pitch needs to be changed to some where around an 5:12 pitch.

Here's a screen shot of my Android Frieze Block Miter Angle & Saw Blade Bevel Angle app showing  Minor Tetra Angle = 22.99236°. This is another good example of the different math functions on different platforms and different devices calculating different angles when the roof is unconstructable to begin with. The Minor Tetra Angle is from an function that I wrote that tries to draw the 2 tetrahedrons for the 2 different pitches. If the 2 tetrahedrons don't align with the hip rafter than the roof is unconstructable.

This image shows an screen shot of the Android Frieze Block Miter Angle & Saw Blade Bevel Angle app where I've changed the minor pitch to an 5:12 pitch, so we can view the results for the Frieze Block Miter Angle & Saw Blade Bevel Angle for both the major roof pitch and minor roof pitch.

This image shows an screen shot of the Android Frieze Block Miter Angle & Saw Blade Bevel Angle app when the View Hip Rafter Angles button is pressed. The hip rafter or valley angles are not needed to cut the frieze blocks, but are shown for reference.

In this screen shot of the Android Frieze Block Miter Angle & Saw Blade Bevel Angle app you can see that the Major & Minor plan angles are set to 0.00 when you enter an Roof Eave Angle of 1356°, which is an unconstructable roof.

Note: the screen shots of my Android Frieze Block Miter Angle & Saw Blade Bevel Angle app are just about the same size of my Google Nexus 7 tablet.