Butterfly Roof Truss Calculator
A butterfly roof truss slopes downward from both outer walls toward a center valley, the inverse of a standard gable roof, giving the building a distinctive V-shaped or "butterfly wing" profile and channeling rainwater to a central gutter or drain. Enter span and pitch below to size a butterfly roof truss.
Size Your Butterfly Roof Truss
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Butterfly Roof Truss Design Considerations
Where a standard gable truss sheds water outward to two side gutters, a butterfly truss does the opposite — each half slopes down toward a shared center point, so all roof water is collected internally and directed to a single central drainage line or valley gutter.
Because the center valley concentrates all of the roof's water flow into one line, butterfly roof designs need a robust, well-sealed central drainage system and careful structural detailing at the low point, where two truss halves meet and the drain penetrates the roof.
Butterfly roofs are popular in modern residential architecture for the clerestory windows they enable at the high outer walls, letting in more natural light than a standard gable — but the added drainage complexity means professional waterproofing detail is essential.
Frequently Asked Questions
What is a butterfly roof truss?
A butterfly roof truss is an inverted roof shape that slopes downward from both outer edges toward a central valley, resembling butterfly wings and channeling all roof water to a single center drain instead of outer gutters.
Why do butterfly roofs need special drainage design?
Because all the water from both roof slopes concentrates at one central valley instead of spreading to two edges, the central gutter and drain must be sized and waterproofed carefully to avoid leaks and overflow at the low point.