The gambrel was a roof with two slopes on each side. A steep slope at the bottom and a gentle slope at the top. The gambrel looked like a barn because the gambrel was a barn. The Dutch brought it to New York and put it on houses and the houses looked like barns and the Dutch did not see a problem because the Dutch built things that worked and worried about how they looked later.

The gambrel made a room. The steep lower slope gave you headroom that a regular roof did not. You could stand up in the attic of a gambrel house. You could put a bed and a dresser and a window and the attic was a bedroom. The gambrel was the most efficient roof in architecture. Every square foot of roof became a square foot of living space. The regular roof wasted the triangle. The gambrel used it.

The gambrel had a mathematical elegance. The lower slope was about sixty degrees and the upper slope was about thirty degrees and the break between them was called the curb. The curb was where the geometry changed. Below the curb the roof was almost a wall. Above the curb the roof was almost flat. The gambrel was two roofs in one and neither roof knew it was sharing.

You could spot a gambrel from three blocks away. The silhouette was unmistakable. A straight-sided house with a bent roof. Brooklyn was full of them. The Dutch farmhouses in Flatbush had gambrel roofs and some of them are still standing. Three hundred years old and the gambrel is still keeping the rain out. The flat roof on the new building next door is seven years old and it leaks. Three hundred years versus seven years. The math is not close.

They do not build gambrel roofs anymore. The gambrel requires a carpenter who understands geometry and a framer who can cut the curb joint where the two slopes meet. The curb joint is the hardest joint in roofing. Get it wrong and the roof buckles. Get it right and the roof lasts three hundred years. They build flat roofs because flat roofs do not have a curb joint. The flat roof has no hard part. The gambrel was all hard parts. The hard parts are why it is still standing.

See also: Gable, Ridgepole