Hip-roof

A hip roof, hip-roof or hipped roof, is a type of roof where all sides slope downwards to the walls, usually with a fairly gentle slope (although a tented roof by definition is a hipped roof with steeply pitched slopes rising to a peak). Thus a hipped roof house has no gables or other vertical sides to the roof.

A square hip roof is shaped like a pyramid. Hip roofs on houses could have two triangular sides and two trapezoidal ones. A hip roof on a rectangular plan has four faces. They are almost always at the same pitch or slope, which makes them symmetrical about the centerlines. Hip roofs often have a consistent level fascia, meaning that a gutter can be fitted all around. Hip roofs often have dormer slanted sides.

Hip roofs are more difficult to construct than a gabled roof, requiring more complex systems of rafters or trusses. Hip roofs can be constructed on a wide variety of plan shapes. Each ridge is central over the rectangle of the building below it. The triangular faces of the roof are called the hip ends, and they are bounded by the hips themselves. The "hips" and hip rafters sit on an external corner of the building and rise to the ridge. Where the building has an internal corner, a valley makes the join between the sloping surfaces. They have the advantage of giving a compact, solid appearance to a structure. The roof pitch (slope) may vary.

In modern domestic architecture, hip roofs are commonly seen in bungalows and cottages, and have been integral to styles such as the American Foursquare. However, the hip roof has been used in many different styles of architecture and in a wide array of structures.

A hip roof is self-bracing, requiring less diagonal bracing than a gable roof. Hip roofs are thus much better suited for hurricane regions than gable roofs. Hip roofs have no large, flat, or slab-sided ends to catch wind and are inherently much more stable than gable roofs. However, for a hurricane region, the roof also has to be steep-sloped; at least 35 degrees from horizontal or steeper in slope is preferred. When wind flows over a shallow sloped hip roof, the roof can behave like an airplane wing. Lift is then created on the leeward side. The flatter the roof, the more likely this will happen. A steeper pitched hip roof tends to cause the wind to stall as it goes over the roof, breaking up the effect. If the roof slopes are less than 35 degrees from horizontal, the roof will be subject to uplift. Greater than 35 degrees, and not only does wind blowing over it encounter a stalling effect, but the roof is actually held down on the wall plate by the wind pressure.

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Wikipedia