Fixed Ridge Height
Rafter Calculator
Math Notes and Diagrams
Imperial Units Rafter Calculator
JLC Thread ... Fixed Ridge Height and Rafter Pitch
JLC Thread ... The math, please
x
=
y
=
Plate Width
=
design to
...
Heel Height
Rafter Depth
Depth ÷ 3
Depth ÷ 4
Depth ÷ x
Pitch Angle
x ÷ 12
enter
Design Value
...
x
+ Plate Width ...
x
1 =
y
– Heel Height ...
y
1 =
y
– Plumb Cut ...
y
2 =
Rafter Length =
Rafter Depth ...
r
=
Plumb Cut Depth =
Heel Height (HAP) =
Plumb Cut Depth – HAP =
% material remaining =
arctan (
y
1/
x
1) ... θ =
Rise over 12 =
Check Rafter Pitch Angle
arctan (
y
2/
x
) ... θ =
Check Plumb Seat Depth
Plate Width × tan θ =
Diagonal Calculations
origin to ridge (
x
,
y
)
Ö
(
x
² +
y
²) =
arctan (
y
/
x
) ... φ =
Diagonal Angle =
Check Rafter Pitch Angle
φ – Diagonal Angle =
Circle Calculations
center at ridge (
x
,
y
)
Radius ...
R
=
Distances from Ridge (
x
,
y
)
to Point of Tangency with
r
Δ
x
=
Δ
y
=
Distances from Origin to
Point of Tangency with
r
*
x
=
*
y
=
Check Rafter Depth
Ö
(*
x
² + *
y
²) ...
r
=
Check Rafter Pitch Angle
arctan (Δ
y
/Δ
x
) ... θ =
arccos calculation ... θ =
