Purlins In Roof Truss

To strengthen the roof system truss clustering cross bracing and wind bracing is recommended at both end of the buildings and every 20 for longer span buildings.

Purlins in roof truss. The longitudinal horizontal beam that is sitting on a post or the principal rafter of a truss and used to support common rafters. 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. Generally the purlins are so spaced that they are supported over the top chord joints of the truss. In order to compensate for this differing geometry thickness of roof purlin adjusted for roof slope needs to be taken into account.

The purlin are ultimately used to fasten the roof steel providing a diaphragm effect along with the siding when properly engineered and installed. A common arrangement is a rafter and purlin system which combines purlins and rafters. Purlins are beams of light sections spanning between trusses carrying dead load of roof live load and wind load. Purlin plates under purlin principal purlins and common purlins.

Parts of a roof gutter. Purlins transmit these loads to the trusses. Homes with gambrel roofs. Further to be considered is the roof framing system as a whole be it truss or rafters wood or steel as the case may be is a factor how purlins are installed at calculated distances apart.

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. There are three types of purlins in wood construction. To the good folks in michigan the only way to construct a pole building is to place the columns every eight feet. Under purlins were typically propped off internal walls.

Types of roof trusses. Spacing is typically 24 on center in low snow loads and is reduced based upon truss span and snow load. Purlins 24 oc are typical along with the bottom bracing shown. At interior trusses purlin tops are even with top of truss.

At ends purlin bottoms are across top of truss. 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. In traditional timber truss construction purlins rest on the principal rafters of the truss.