Butterfly roofs
Two planes sloping inward to a central valley, like an open book. A mid-century modern signature, and entirely dependent on that central channel working.
- Typical pitch
- Low, usually under 4:12
- How often we see it
- Rare
Pitch ranges are trade convention, not code. Code sets minimum slope by material, not by roof shape.
Is this your roof?
- The roofline dips in the middle instead of peaking.
- From the side the outline is a shallow V.
- Usually on a mid-century modern or architect-designed house.
In Johnson County
A butterfly roof deliberately collects all of its water into one channel, which in Kansas means a very large volume arriving very fast during a summer thunderstorm. If the internal drain blocks, the roof has nowhere to send that water and it backs up over the membrane. These roofs are not inherently problematic, but they are unforgiving of deferred maintenance in a way a gable simply is not. Clearing that drain is not optional here.
What you can put on it
Material choice on this shape, and where code rather than preference makes the decision for you.
Membrane (TPO, EPDM, modified bitumen)
Works wellThe central valley is effectively a low slope roof, so it needs a membrane even where the wings are steep enough for shingles.
Standing seam metal
WorkableSuits the architecture, but the central channel detail has to be fabricated and is unforgiving.
Asphalt shingles
Specialist onlyPossibly acceptable on the wings if their pitch supports it, but never in the central valley.
What we check first
The failure points that are specific to this shape, in the order a roofer looks at them.
- The central valley membrane, end to end.
- The internal drain or scupper, for blockage and for the condition of the surrounding flashing.
- Evidence of previous ponding along the channel.
- The transition where each wing meets the central valley.
What moves the price
Square footage is a poor predictor on its own. These are the things that actually change the number on this shape.
- The central valley is the job. Everything else is straightforward by comparison.
- Drainage is usually internal, so the roof work is tied to plumbing that has to be right.
- Often architect-designed with non-standard dimensions, so components get fabricated rather than bought.
- Few crews quote these, so pricing varies widely between contractors.
Common questions
Are butterfly roofs a bad idea in Kansas?
Not bad, but demanding. The shape funnels the entire roof's water into one central channel, and our storms deliver a lot of water in a short time. That is fine when the membrane is sound and the drain is clear, and it becomes a problem quickly when either is neglected. If you own one, that drain needs to be on a maintenance schedule.
Can a butterfly roof be shingled?
The central valley cannot — it is a low slope condition and needs a membrane. The wings might take shingles if their pitch is 2:12 or greater, per the 2018 IRC, section R905.2.2, but mixing systems on a roof this dependent on one detail is rarely worth it. Most butterfly roofs are best done as a single membrane system.
Do you work on mid-century modern butterfly roofs?
Yes, and we get called for them specifically because many crews will not quote them. They need a membrane approach and a fabricated central detail rather than an off-the-shelf one. We will scope it honestly and tell you if the existing drainage design is the real problem rather than the roof covering.
More answers on the roofing questions page, or see every roof shape side by side.
Often confused with
Flat and low slope
Anything under 2:12. Not actually flat — a working low slope roof always has some fall built in — and it needs a membrane rather than shingles.
Shed and skillion
A single plane sloping one way, with no ridge. Common on additions, porches, dormers and modern infill homes.
Hexagonal and polygonal
Six or more planes meeting at a point, over a bay window, a turret or a gazebo. Small in area, disproportionate in difficulty.
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