What is a butterfly roof?
A butterfly roof, also called a V-roof, is a roof with two planes that slope down towards the middle and meet at the lowest point. In section the roof forms a V, like the raised wings of a butterfly. It is essentially an inverted gable roof: instead of a ridge, there is a gutter in the centre. In Dutch it is called ‘vlinderdak’ or ‘V-dak’.
How it works
All rainwater runs to the centre into a valley gutter or box gutter along the full length of the roof. That gutter drains to the end walls, where the downpipes are, or to internal roof outlets. The advantage: the long elevations need no gutters or downpipes, which gives clean facades. Designers sometimes make a feature of the outlet, for example a spout or water chute on the end wall.
Application
- Modern houses and pavilions, where the high roof edges leave room for tall windows on both long sides.
- Buildings with rainwater harvesting: all the water collects at one point, ideal for a water butt or storage tank.
- Garages, outbuildings and extensions with a contemporary look.
Tips and points of attention
- The gutter is the weak point. It carries the water from both roof planes. A blocked or undersized gutter overflows into the building instead of spilling over an eaves edge outside.
- Fall in the gutter: the gutter itself must slope towards the outlet. Standing water encourages leaks and dirt.
- Plan overflows: provide an emergency roof drain or overflow at every low point, so that if an outlet blocks, the water escapes visibly outside rather than loading the roof.
- Leaves and snow: debris and snow collect in the valley. Fit leaf guards and have a structural engineer allow for the extra snow load that drifts into the V.
- Waterproofing: use a continuous, preferably seamless membrane or gutter lining at the lowest point and detail the junctions with extra care.
- Maintenance: inspect the gutter regularly, especially in autumn.
Related terms
- Roof shape
- Gable roof
- Mono-pitch roof
- Valley gutter
- Box gutter
- Emergency roof drain
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