Gambrel Roof

A gambrel roof is a symmetrical roof with two slopes on each of its two sides: a steep lower pitch rising from the eaves and a shallower upper pitch meeting at the ridge. The ends are vertical gables. Because the lower slopes are steep, a gambrel encloses much more usable space than a simple gable roof of the same height, which is why it is strongly associated with barns and with two-storey houses whose upper floor sits within the roof.

The term is thought to derive from an older word for the hock of a horse's hind leg, which the bent profile resembles. In British English the same form is often called a curb or kerb roof; the horizontal line where the two pitches meet is the curb.

Gambrel versus mansard

Both are curb roofs with two pitches per side. A gambrel has two roof sides and gable ends; a mansard is hipped, with two pitches on all four sides. In continental Europe "mansard" is sometimes used for both.

History and use

• North America: gambrel roofs appear on houses of the 17th and 18th centuries in New England and the Dutch-influenced Hudson Valley. A common form is seen on the 1752 Captain Joseph Atwood house in Chatham, Massachusetts. In the 19th and 20th centuries the gambrel became the classic profile of the American barn, where the large loft stored hay, and it was later revived in Dutch Colonial Revival houses.
• Europe: similar double-pitched profiles appear on barns and houses in Britain and continental Europe, where they are often grouped with mansards.

Considerations

• The break in slope (the curb) needs careful framing and flashing; the shallow upper slope may need extra underlayment or a low-slope-rated covering.
• The flat gable ends present a large area to wind, so bracing matters in high-wind regions.
• Snow can accumulate at the curb on the lower slope.
• Gambrel trusses are widely available, making the form popular for sheds, garages and outbuildings.