What This Calculator Does
A roof valley forms where two roof planes meet. The line is not guessed by eye. It follows the intersection of two sloped planes. This calculator converts common pitch inputs into practical valley angles. It also estimates valley slope, actual rafter length, rise, plan bearings, and total stock length.
Why Valley Angles Matter
Valley geometry controls layout, cutting, flashing, and material waste. A small pitch difference can move the valley line away from a simple forty five degree plan. That change affects jack rafter marks and valley board length. Unequal pitches also create a valley slope that differs from both roof slopes. Good numbers reduce trial cuts and help crews prepare safer layouts.
Using Plan Angle and Pitch
The plan angle describes the corner seen from above. Many roofs use ninety degrees, but additions and dormers may not. Each roof pitch is entered as rise per twelve units of run. The tool changes those pitches into plane slopes. It then builds two roof plane normals and finds their intersection. That intersection gives the valley direction and its true slope.
Material Planning Benefits
The projected valley length is the flat plan distance. Actual valley stock is longer because the rafter rises along the roof. Overhang and waste inputs give a better order quantity. The calculator also multiplies by the number of matching valleys. This is useful for hips, dormers, porch tie ins, and repeated roof bays.
Practical Notes
Use the output as a geometry guide. Field framing can change with sheathing thickness, ridge depth, fascia details, and local practice. Always confirm dimensions on the actual roof. Check plans, building codes, and manufacturer instructions before cutting costly material. For complex roofs, compare the calculated plan angle with a scaled drawing. When both match, layout confidence improves.
The result table is designed for record keeping. It shows both decimal and angle values, because different workers prefer different references. The CSV button saves the main figures for estimates. The PDF button creates a simple job note. Keep a printed copy with sketches, roof pitch notes, and site measurements. That habit makes later checks easier.
It also helps reviewers trace assumptions before approving layout changes. Use it before ordering materials too.