Purlins In Roof Truss

Under purlins were typically propped off internal walls.

Purlins in roof truss.

Spacing is typically 24 on center in low snow loads and is reduced based upon truss span and snow load. 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. 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 transmit these loads to the trusses.

Generally the purlins are so spaced that they are supported over the top chord joints of the truss. 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. The purlin are ultimately used to fasten the roof steel providing a diaphragm effect along with the siding when properly engineered and installed. Parts of a roof gutter.

Purlins 24 oc are typical along with the bottom bracing shown. 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. Purlin plates under purlin principal purlins and common purlins. It is understood that purlins are spaced where laps and splices of roof sheets that vary in sizes.

There are three types of purlins in wood construction. In traditional timber truss construction purlins rest on the principal rafters of the truss. 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. In order to compensate for this differing geometry thickness of roof purlin adjusted for roof slope needs to be taken into account.

In post frame construction roof purlins are the members running the lengthwise direction of the building either placed on top of or between the roof trusses or rafters to attach the roof steel or other roof sheathing to. Purlins are beams of light sections spanning between trusses carrying dead load of roof live load and wind load. At interior trusses purlin tops are even with top of truss. To the good folks in michigan the only way to construct a pole building is to place the columns every eight feet.

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. Types of roof trusses. At ends purlin bottoms are across top of truss.