Roof Purlin And Truss Spacing

For small spacing of trusses while the purlins become light and less costly the trusses will work out to be costly.

Roof purlin and truss spacing.

These standards are as follows. Using table 52 2 add length shown example. For heavier material such as gage steel the metal roof purlins spacing length could go up to 4 feet. Installation of pole barn purlins.

4 12 slope and 2 6 rake purlins 1 13 16 to first rake purlin spacing only and draw marks on truss top accordingly. Spacing is typically 24 on center in low snow loads and is reduced based upon truss span and snow load. The purlin are ultimately used to fasten the roof steel providing a diaphragm effect along with the siding when properly engineered and installed. Load tables specifying safe loads for different spans are available from metal deck manufacturers.

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. Here is the formula for calculation of a roof purlin. It is understood that purlins are spaced where laps and splices of roof sheets that vary in sizes. The roof truss structure and design is integral to roof structural integrity and shape.

This article and series of illustrated diagrams shows you all the parts of a basic roof truss king truss and queen truss. Purlins are dimensional lumber that are fastened to the top chord of trusses connecting them together for bracing purposes. The economic spacing of trusses means the spacing at which the overall cost of trusses purlins roof cover columns etc. The spacing of purlins on roofs and girts on wall is usually 4 to 6 ft.

The typical spacing standards for residential and commercial buildings are about 1 to 2 foot. The spacing of purlins usually call for careful arrangement in the sense that it should follow the nodal pattern of the supporting trusses. There are many types of roof trusses as wall as many types of roofs more types than there are parts. In addition each roofing truss will be made of a two by four piece of lumber or in areas with expected or usual heavy snow fall there will be trusses which are two inches by six inches.

Cos of live load dead load x cos of the purlin spacing x purlin span squared 8 x sm section modulus of the member x duration of load 1 15 in areas with snowfall x cr repetitive member factor of 1 15 where members are 24 on center or less fb fiberstress required. Numbers 20 and 22 u s. Typical roof truss spacing means that they are usually about 24 inches from centre which means at the centre of one truss there will be a two foot gap or twenty four inch gap until the centre of the next truss. Also important to note here is that a two inch in a.

Standard gage are generally used for roofing. What i mean in this regard is that purlins should be placed at the nodes of trusses and not on the members themselves so as not to induce secondary bending and shear forces in the members of the truss.