The Gambrel roof, like the mansard roof, has two distinctly different slopes on each of its two symmetrical sides. The bottom slope has a steep pitch, sometimes nearly vertical while the top slope is lower. But unlike the mansard roof, the gambrel roof only utilizes this method on two sides of the structure rather than four.
The gambrel is often referred to as a barn roof, in that it is commonly seen on many hay barns for the ample space it provides for storage. Small structural additions called dormers may also be seen on gambrel roofs as to provide more head space or extra lighting. This allows for the extra space found in gambrel roofs to be used more effectively.
You can find gambrel roofs on a lot of Dutch Colonial architecture from the 1700's and into the 1800's. The name derives from gamba, a Latin word meaning the leg or hoof of an animal.