Roof Purlin Design

In structural steel or aluminum construction p urlins usually w shapes or channels transfer roof loads to the major structural elements supporting the roof.

Roof purlin design.

Roof purlin design roof purlin design. A single shell roof is also called warm roof and it is an unventilated roof. Purlin plates in wooden construction. A purlin plate in wood construction is also called an arcade plate in european english under purlin and principal purlin.

A distinction is made between single shell and double shell roofs. The roof frame work mainly consists of purlins inferior purlin central purlin and ridge purlin ridge collar rafter and roofing battens. As structural members they resist loads and provide lateral restraints for truss members therefore it is important to design them properly against forces. In timber construction purlins are nailed to the rafter or supporting trusses while in steel roof construction they are welded or bolted to the rafters or trusses by the means of cleats.

The term plate means a major horizontal supporting timber. Metal roof purlins are installed horizontally under metal roofs. Purlin plates are beams which support the mid span of rafters and are supported by posts. They are installed on top of the roof rafters with a felt underlayment or vapor barrier installed on top.

This spreadsheet is to be used to check the adequacy of roof purlins for a specified combination of loads. By supporting the rafters they allow longer spans than the rafters alone. They give added support to the roof and also provide a nailing surface for the end panels and drip edge. Purlins are 2 by 4 feet and are installed much like metal roofing.

The type and spacing of purlins is a design consideration which depends upon the incident roof loads as well as the limiting lengths of sheeting to be used.