Roof Framing Purlin

The purpose of purlins.

Roof framing purlin.

Purlins are installed horizontally under metal roofs. Purlins are 2 by 4 feet and are installed much like metal roofing. In architecture structural engineering or building a purlin or historically purline purloyne purling perling is any longitudinal horizontal structural member in a roof except a type of framing with what is called a crown plate. Purlins are an important component in a pre engineered steel structural kit.

Welded together they can be used as columns braces and ties. Purlins support the loads from the roof deck or sheathing and are supported by the principal rafters and or the building walls steel beams etc. A common arrangement is a rafter and purlin system which combines purlins and rafters. Dead load will be the actual weight of the roof steel and the roof purlins.

The shape of cee purlins does not allow end lapping they are butted together. Hip rafters are simply called hips and are shown here as brown. Hip roofs have hip rafters which are oriented diagonally to the ridge and outside walls. The roof support system is a ridgepole and either rafters which run perpendicular from the top of the walls to the ridge or purlins which run parallel to the ridge.

In architecture or structural engineering or building a purlin or purline is a horizontal structural member in a roof. Hips rest on an outside corner at the bottom and connect to. They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top. Also known as sheeting rails purlins create the roofing members of the secondary framing of a steel building.

Photo above is from a jwk inspections framing pre drwall inspection in the san antonio south teaxas area showing the actual roof framing componenents. The cos of the purlin spacing is because the load on the purlins is vertical and the purlin spacing is with the run of the roof. Cee purlins are secondary steel framing members most commonly used as roof purlins wall girts and header jamb and sill for windows and doors on metal buildings. For sake of discussion we will assume a minimal roof snow load of 20 psf pounds per square foot and a 4 12 roof slope.

Purlins are not required or needed unless rafters are overspanned and then the purlins serve as support to prevent roof sag deflection due to the overspanned and or undersized rafters.