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` = "Gambrel Rafter Lengths"`

Enter a value for all fields

The **Gambrel Rafter Lengths** calculator computes the upper and lower rafter lengths, attic width and total height based on the upper and lower pitch, span and loft height.

**INSTRUCTIONS**: Choose units and enter the following:

- (
**S**) Span of Roof - (
**LH**) Loft Height - (
**P1**) Lower Pitch - (
**P2**) Upper Pitch

**Gambrel Rafter Length (RL)**: The calculator returns the following:

- (
**LR**) Lower Rafter Length - (
**UR**) Upper Rafter Length - (
**TH**) Total Height - (
**LW**) Loft Width

The Loft Width must be less than the span. With that constraint, the rest is simple trigonometry of triangle.

- LR = LH / sin(P1)
- x = sqrt(LR
^{2}-LH^{2}) - LW = S - 2x
- y = LW/2
- UR = (LW/2) / cos(P2)
- z = sqrt(UR
^{2}- y^{2}) - TH = LH + z

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