Butterfly Roof

A butterfly roof, also called a V roof, is formed by two roof surfaces that slope downward from opposite outer edges to meet in a valley near the middle of the building. The profile resembles the wings of a butterfly, or an open book. The outer walls are tall, allowing large clerestory windows and a sense of openness, while rainwater collects in the centre.

History

• Le Corbusier first used the form in 1930 for the Maison Errázuriz, a holiday house in Chile.
• Other early modernist examples include Antonin Raymond's house in Japan (1933), Oscar Niemeyer's Pampulha Yacht Club in Brazil (1943) and Marcel Breuer's Geller House project on Long Island (1945).
• In the late 1950s the architects William Krisel and Dan Palmer popularised the form in Palm Springs, California; from 1957 their Alexander tract developments produced nearly 2,000 houses, many with butterfly roofs. It became an emblem of American mid-century modern design.
• In British cities, a similar V-shaped roof hidden behind a front parapet is found on many Georgian and Victorian terraced houses, where it is known as a London roof.

Drainage

Butterfly roofs typically have no perimeter gutters. Water runs to the central valley and out at one or both ends, often through a scupper into a downspout or water feature. The valley may itself be sloped, or flat with a central cricket that sends water toward the ends. The concentration of water in one place makes the valley lining, outlets and overflow provisions critical, and debris or snow can accumulate there.

Advantages and drawbacks

• Tall outer walls allow generous glazing and daylight.
• The form suits rainwater harvesting, since water is collected at one point.
• The planes can carry solar panels.
• The central valley is a single point of failure for leaks, and the form is generally more complex and costly to waterproof than a gable roof.