Roof Truss Rafter And Purlin

Parts of a traditional queen post roof truss.

Roof truss rafter and purlin.

The longitudinal horizontal beam that is sitting on a post or the principal rafter of a truss and used to support common rafters. This is the right way to fix truss clips connecting the rafter and wall plate. There are three types of purlins in wood construction. A purlin plate in wood construction is also called an arcade plate in european english under purlin and principal purlin.

Under purlins were typically propped off internal walls. For example an 8 x 4 under purlin would support the center of a row of 6 x 2 rafters that in turn would support 3 x 2 roof purlins to which the roof cladding was fixed. It is especially preferable to use in huge room that lacks trusses to create overhead effect despite the fact that trusses are used for practical purpose in the first place. A truss roof using factory made trusses which are delivered to site complete and just erected.

A common arrangement is a rafter and purlin system which combines purlins and rafters. Purlin plates are beams which support the mid span of rafters and are supported by posts. The rafter and purlin spacing for metal roof must be fitted to support the whole. 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.

They transmit the live load dead load wind load which is considerable in large steel structures with low permiability an. In lightweight timber roof construction under purlins were used to support rafters over longer spans than the rafters alone could span. Purlin plates in wooden construction. By supporting the rafters they allow longer spans than the rafters alone.

A cut roof this is the traditional method of cutting the timber on site and building up the roof using rafters ridge boards joists and purlins etc the exact details being determined by the size of roof size of timbers etc. Purlin plates under purlin principal purlins and common purlins. Rafter boards are fastened to the ridge board at the peak and the top plate where they join the wall. Purlins might be attached to rafters while rafter should support all laps and joins.

The term plate means a major horizontal supporting timber. Purlin and rafter are the basic members of any roof structure. The boards creating the slope of the roof are wider than lumber used to build trusses 2x8s 2x10s and 2x12s are most common in rafters vs. Note that these are normally only required to trussed rafter roofs and not for traditional purlin and rafter roof construction.

As structural members they resist loads and provide lateral restraints for truss members therefore it is important to design them properly against forces such as bending shear torsion buckling etc.