How is a pitch change handled on a metal roof?
Short answer. A pitch change on a metal roof, where a steeper slope meets a flatter one or the reverse, is handled with a transition flashing that bridges the bend, plus closures and sealant under the trim, or with panels bent at the break on some standing seam systems. The detail has to keep water flowing over the joint while letting panels move, because pitch changes are a common leak point.
Two kinds of transition
- Concave, steep to shallow: such as a main roof flattening into a porch. Water slows at the bend, so the transition trim must lap over the lower panels with closures underneath.
- Convex, shallow to steep: such as a mansard or gambrel break. The upper panels lap over a transition trim that turns down onto the steeper slope.
Typical detail for exposed-fastener panels
- Install the lower slope's panels up to the break.
- Place closures and butyl tape on the lower panels.
- Fasten the transition trim over them, formed to the bend angle.
- Run the upper panels down over the trim's upper flange, with closures and tape beneath.
Standing seam options
Some standing seam systems allow panels to be bent at the break in the field, keeping one continuous panel. Others use a transition flashing with cleats. The manufacturer's detail decides, and the lower section must still meet the panel's minimum slope.
Common problems
- The lower section is too flat for its panel type.
- Missing closures that let wind-driven rain under the trim.
- Laps installed the wrong way.
- Leaves and pine straw collecting at the bend on low porch roofs.
Mixed materials
Where a shingle main roof meets a metal porch roof, or the reverse, the transition needs flashing designed for both materials, and the underlayment should run continuously beneath the joint.