Roof Types, Components & Terminology

Roof Types Gable Roof – The most common roof style, the gable roof consists of two sloping surfaces that meet at the top to create a simple triangular roof

Roof Types Shed Roof – A roof that slopes only in one direction, sometimes referred to as a lean-to.

Roof Types Hip Roof – Another common roof style, the hip roof slopes upward from all exterior walls, eliminating gable ends.

Roof Types Intersecting Roof – Required on buildings that are not simply a “box” and have portions of the building that “stick-out” from the main structure of the house. Whenever two roofs intersect, valleys are formed.

Roof Types Gambrel Roof – a variation of the more common gable roof, the Gambrel adds a second slope to each side of the standard gable roof, with the lower slope being much steeper than the upper.

Roof Types Mansard Roof – Variation of the hip roof, with two slopes per side. Similar to a Gambrel Roof but on a Hip rather than a Gable end.

Roof Types Butterfly Roof – An inverted gable roof, most commonly found on modern architecture.

Roof Framing Members

Roof Framing Members Ridgeboard – The upper most member of a roof, used to simplify the construction of the roof, although it is not necessarily required for structural purposes. The upper ends of the rafters attach to the Ridgeboard.

Roof Framing Members Common Rafter – Named because they are the most common member on any roof, they span from the Ridgeboard to the exterior walls. They are used as a starting point for all other rafters (calculations for other rafter types are based on this “template.”)

Roof Framing Members Hip Rafter – Hip Rafters form an intersection between two roof sections. They usually run at a 45 degree angle from the top plates and are used to form outside corners of the roof.

Roof Framing Members Valley Rafter – These are also used to create intersections of two roofs but project inward, creating an inside corner.

Roof Framing Members Jack Rafter – Jack rafters come in three types and are basically common rafters that land on a hip, valley or both. Hip Jack Valley Jack Cripple Jack

Roof Framing Members Collar Ties – Horizontal members that add strength to the common rafter, tying the rafters together on each side of the Ridgeboard, somewhere above the ceiling joists.

Roof Framing Members Gable End Studs – These are used to frame in the triangular wall beneath a Gable Roof.

Roof Framing Terms

Roof Framing Terms Unit Run – The Unit Run is the horizontal distance under a rafter. This distance is always 12 inches for a common rafter. It is 16.97 inches (17”) for hip and valley rafters.

Roof Framing Terms Total Span – The horizontal distance covered by the roof, measured from outside wall to outside wall.

Roof Framing Terms Unit Rise – The distance the roof will rise vertically in inches for every unit of run. Example If the unit rise is 6”, then the common rafter will rise 6” for every 12” it covers horizontally.

Roof Framing Terms Total Run – The total horizontal distance over which the rafter slopes (usually one half o the total span of the roof).

Roof Framing Terms Total Rise – The total distance vertically from plate to ridge.

Roof Framing Terms Theoretical Line Length – The length of the Rafter from the plate to the ridge. It is the hypotenuse of the right triangle formed by the total run as the base and the total rise as the vertical leg.

Roof Framing Terms Unit Length – The length of rafter needed to cover a horizontal distance of one unit of run. It is the hypotenuse of the right traingle formed by the unit run and unit rise.

Roof Framing Terms Pitch – a fraction that represents the amount of incline of a roof. The pitch is found by dividing the rise by the span. Example: If the total span is 32feet and the rise is 8ft, the pitch is 8/32 which reduces to ¼. The roof is said to have a ¼ pitch.

Roof Framing Terms Slope – the common term used to express the steepness of a roof. It is written as a proportion - unit rise to unit run (which is always 12”) Example: If the unit rise is 4”, the slope is expressed as 4:12

Roof Framing Terms Bird’s Mouth – refers to the notch cut out of a rafter that allows the rafter to sit on the top plate.

Roof Framing Terms Rafter Stand – Rafter stand of height above plate (HAP) is the part of the rafter stock that remains after the Bird’s mouth has been notched. It is measured vertically (plumb).

Roof Framing Terms Plumb Line – Any line on a rafter that is vertical after the rafter is in place. There is always a plumb line on the ridgeboard, wall and at the tail of the rafter if installed correctly.

Roof Framing Terms Level Line – Any line on the rafter that is horizontal after the rafter is installed.

Trusses A Roof Truss is an engineered structural component that is used to replace ceiling joists, roof rafters, collar ties, ridgeboards, etc. A Roof Truss is typically a single unit that is used in conjunction with a series of other trusses to create the entire roof structure. Trusses require less wood to manufacture and can typically be engineered to accommodate larger spans and loads.

Types of Trusses

Parts of a Truss

Truss Layout