Ideas Library · Roof Design
Butterfly Roof: Raising the Edges and Draining Down the Middle
Turn the roof the other way up so its high points are at the perimeter and its low point is in the middle, gaining glazing along the raised edges and accepting a single internal drainage line.
Spaces:Whole roofClerestory bandCentral valleyRoom beneath the planes
Style:Mid-century-inspiredContemporarySculpturalModern-minimal
Where this idea works
Where this idea works
Contexts this direction tends to suit — and, honestly, where it may not.
- Deep plans where daylight is wanted from two opposite sides at high level
- New builds and extensions where the roof geometry is genuinely open
- Owners drawn to a roof that reads as two lifted planes rather than a mass
- Settings where a low central line keeps the apparent height down
Where it may not fit
Where it may not fit
- Sites with heavy leaf fall or exposure where a central valley could be obstructed — a question for a qualified professional
- Buildings where an internal drainage route cannot be inspected or reached — confirm access first
- Situations expecting a conventional roof profile — confirm with the relevant authority
Planning
Planning considerations
- The whole point of the form is the raised perimeter, so plan the glazing it makes possible at the same time
- A central valley sits inside the building line, so anything overtopping discharges into the construction rather than clear of it
- A secondary route for water when the primary outlet is obstructed stops being optional on this form — confirm it with a qualified professional
- Falls, outlets and their positions shape the ceiling beneath, so settle them with the room in view
Layout
Layout considerations
- Daylight arrives high on two opposite sides, which suits a plan that is deep rather than long
- The ceiling can follow the two planes and rise toward the windows at both edges
- The valley line usually wants a structure beneath it, so place walls or a beam where it lands
- Raised edges change what the building overlooks, so test the clerestory sightlines both ways
Materials & finishes
Materials and finishes to discuss
Named generically as starting points to discuss with professionals — not specifications, and not priced.
Consider:Single ply or liquid applied membraneStanding seam metal coveringClerestory glazing unitsValley gutter and outletsOverflow or secondary outlet
- Ask how the valley and its outlets behave when obstructed, since water is retained rather than shed
- Discuss which coverings suit the shallow falls this form tends to produce
- Confirm how the raised edges are weathered where they are most exposed
Maintenance & durability
Maintenance and durability questions
- The valley collects everything the roof carries, so clearing it is a recurring job — discuss access
- Ask how the outlets and any overflow are reached and checked over time
Professional review
What to ask a qualified professional
Bring these questions to a designer, contractor or the relevant qualified professional or authority.
- How would you provide and prove a secondary drainage route for a valley inside the building line?
- Which coverings would you suggest discussing for the falls this form produces?
- Would the inverted structure change how loads reach the walls in ways you would need to assess?
- How would the valley and its outlets be reached for clearing once the building is finished?
- Are there height or appearance considerations for this form I should confirm with the relevant authority?
More ideas
Related ideas
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Roof Design Ideas
Educational roof design inspiration — roof form, edge condition, the plane seen from above and the shape read from inside, framed as directions to explore before speaking with professionals.
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