While low-slope roofs are generally limited to flat-roof styles and are seldom found on residential structures, steep-roof styles vary greatly.
Of the steep-roof styles, the gable roof is the most common. It has a high point, or ridge, at or near the center of the house or wing that extends from one end wall to the other.
The roof slopes downward from the ridge in both directions. This roof style gets its name from the gable, which is the triangular section of end wall between the rafter plate and the roof ridge.
The roof on one side of the ridge is usually the same size and slope as the roof on the other side. The gable roof of the saltbox house is an exception.
An architecture common in New England, the saltbox has different slopes and slopes of different lengths. A hip roof also has a ridge, but the ridge does not extend from one end of the roof to the other.
The lower edge of the roof, or eave, is at a constant height and the roof slopes downward to the eaves on all sides. The point where two roof surfaces meet at an outside corner is called a hip. The junction where two roof surfaces meet at an inside corner is called a valley.
A shed roof slopes in only one direction, like half a gable roof. The roof has no ridge and the walls that support the rafters are different heights. The shed roof has several variations. One is the butterfly roof, where two shed roofs slope toward a low point over the middle of the house.
In another variation, two shed roofs slope upward from the eaves, but do not meet at a ridge. The wall between the two roofs is called a clerestory, and is often filled with windows to let light into the interior
of the house.
A gambrel, or barn roof, has double slopes: one pair of gentle slopes and one pair of steep slopes. Like a gable roof, the gambrel roof slopes in both directions from a center ridge. At a point about halfway between ridge and eave, however, the roof slope becomes much steeper.
In effect, the lower slope replaces the upper exterior walls of a two-story house. It is common to add projections through the roof, called dormers, for light and ventilation.
Just as a gambrel roof is like a gable roof with two different slopes, a mansard roof is like a hip roof. From a shorter ridge, the roof drops in two distinct slopes to eaves that are the same height all the way around the structure.
Up to 40 percent of the building is roof with the mansard roof design. In addition to typical residential applications, mansard roofs are often used for apartment complexes, commercial buildings, and even institutions such as schools.