Pitch of a Roof Vs. Slope

General Definition of Pitch and Slope

• A roof is considered flat when its pitch is at or below 2 inches high for every 12 inches across. A medium pitch or slope is 4 to 6 inches for every 12. The steepest roofs are 9 to 12 inches of height for every 12 inches in length. Steeper roofs are typically found in climates that have a lot of snow, and flat roofs are found in more temperate zones.

Roof Geometry: Slope

• The primary concern of building codes and regulations is the health and safety of the people who occupy buildings. It is important, therefore, that designers understand the implications of slope in terms of stresses, loads and drainage. Roofs with a greater slope will shed the snow more easily than a flat roof because of gravity. This reduces the weight, or load, that the roof members need to support. A lesser-sloped roof needs to keep enough of an angle to shed water so that it does not pool on the roof and cause a collapse.

Roof Design: Pitch

• The pitch of a roof differs according to the style of the building. An adobe house in the Southwest has a lower pitch, perhaps 2 inches in 12. Bungalow houses in the Chicago area tend to have a pitch of 4 to 6 inches in 12, while cape homes in the Northeast are typically closer to 8 to 9 inches in 12. It is important when creating dormers or additions to be guided by existing pitches. Have too much variation in roof pitch can create a discordant look.

Angle of Incline

• It is sometimes necessary to describe the angle of a roof in terms of degrees. This is the least common terminology because it requires trigonometry to calculate rather than a measuring tape or straightforward geometry. The angle of incline becomes important when photovoltaic panels are being installed for generating electricity. The efficiency of a solar array is significantly impacted by its relationship to the angle of the sun in the sky. This can be calculated by subtracting the angle of incline from 90 degrees.