Purlin Shed Roof

Snap a chalk line horizontally across the roof two feet down from the top.

Purlin shed roof.

Spacing is typically 24 on center in low snow loads and is reduced based upon truss span and snow load. In a structural steel shed the main portal frames and roof rafters are made from strong steel sections which are welded together and later bolted together. First the purlins support the roof. Purlins and girts are used longitudinally to support the roof sheeting which they were originally designed for.

The purlin are ultimately used to fasten the roof steel providing a diaphragm effect along with the siding when properly engineered and installed. This design is a lot stronger and more robust way of making a steel shed. 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. Lay the first purlin at the ridge of the roof down to the chalk line beginning at either corner.

Secondly purlins tie the rafters together stabilizing and strengthening the structure s rigid framing. Purlin roof structure civil engineering design in architecture or structural engineering or building a purlin or purline is a horizontal structural member in a roof. Thirdly purlins add additional support between the spans of the individual framing bays.