Purlin Shed Roof

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.

Purlin shed roof.

Snap a chalk line horizontally across the roof two feet down from the top. Fasten the purlin with 16d common nails into each vertical rafter. This design is a lot stronger and more robust way of making a steel shed. The purlin are ultimately used to fasten the roof steel providing a diaphragm effect along with the siding when properly engineered and installed.

Lay the first purlin at the ridge of the roof down to the chalk line beginning at either corner. Metal building roof purlins provide three structural functions. Purlins and girts are used longitudinally to support the roof sheeting which they were originally designed for. Thirdly purlins add additional support between the spans of the individual framing bays.

Insert two equally spaced nails into the rafter. Spacing is typically 24 on center in low snow loads and is reduced based upon truss span and snow load. First the purlins support the roof.