Dave,
Please note that the simple formulas for determining deck angles from roof pitches
DD = Arctan[Tan(S)/Tan(SS)]
D = Arctan[Tan(SS)/Tan(S)]
do not work for irregular plan, irregular pitch roofs and you need to use the full-blown equations:
DD = Arctan[Sin(W)/( Tan(SS)/Tan(S) + Cos(W) )]
D = Arctan[Sin(W)/( Tan(S)/Tan(SS) + Cos(W) )]
For a given roof, main and adjacent pitches have unique values. Once you have chosen SS and S they are fixed, and cannot be back-calculated by formula.
This is an old topic/post. However, anyone looking for plan angles formulas for deck angles greater than 90° might want to take a look at this page for deck/eave angles greater than 90° with unequal pitched roofs.
Ed's trigonometric formulas only work when the unequal pitched roof have an deck angle somewhere less about 120°. The cosine of an angle greater than 90° is always negative. Also, the plan angle formula should check to see if both calculated plan angles add up to the given deck angle.
Bevel angles for three dimensional connections
Martindale - plan angles Frank L. Martindale had the correct plan angle formula along. It's similar to what I use.
One of the problems with roof framing trigonometry, is unconstructable roof framing.
unconstructable roof framing Sim
