A gambrel roof is a two-sided roof with a central ridge. Each side has two sloping surfaces. The upper surface is shorter in length and has a gentle slope of about 30 degrees, while the lower surface is longer and has a sharper slope of about 60 degrees. Gambrel roof trusses are made with shorter pieces of lumber joined together, rather than the very long pieces of lumber needed for roofs like the A-frame.
The great advantage of the gambrel roof is that it provides a surface that is very resistant to damage from weather. At the same time, the gambrel roof provides a large amount of interior space. Because the weight of the roof is supported by trusses that direct the stress to the building's exterior walls, weight-bearing interior walls or posts are unnecessary.
The name for a gambrel roof may come for the Middle English word gambril, which referred to a "hooked or crooked stick" and could also be spelled as gamrel or gameral. In 17th century England, the word gambrel was sometimes used for a horse's hock, the joint in the animal's hind leg that gives the leg its crooked appearance.
However it got its name, the gambrel roof was popular in Europe during the 16th and 17th centuries, and there are written records of buildings with a gambrel roof in North America as early as 1737. This kind of roof was prominent in Dutch Colonial building, and has appeared in Colonial Revival buildings. Sometimes the roof was extended beyond the gable end of the building, forming a protected area beneath the overhang at each end.
In the midwest, the gambrel roof was frequently used on hay barns. The ample storage space allowed by the shape of a gambrel roof explains its popularity. It has been so frequently used for such a long period of time that in some areas a gambrel roof is called a "barn roof."
The gambrel roof is becoming popular again today. Often, dormers are set into the roof to allow for windows. Sometimes the extended roof at the gable ends shelters large windows. The large, open, brightly lit interiors give homeowners plenty of usable space.