Roof Purlin Deflection Criteria

Roof sheathing is at least 7 16 thick oriented strand board or plywood.

Roof purlin deflection criteria.

Z section purlins 10 c section trimmer 51 side rails 28 7 metsec uk leaders in the design and manufacture of engineered and bespoke purlin and side rail building solutions. Other than plaster or gypsum board. Plaster or gypsum board. The cos of the purlin spacing is because the load on the purlins is vertical and the purlin spacing is with the run of the roof.

For example the allowable deflection of a 12ft span floor joist with plaster l 360 is 0 4 12ft divided by 360. Mean roof height is not greater than 40 feet. 3 mezzanine beams and joists. Dead load will be the actual weight of the roof steel and the roof purlins.

Introduction and components roof systems 10 23 eaves beams 24 27 side rail systems 28 53 ancillary items 54 59 load tables 60 78 mezzanine floor systems 79 85. Monorail crane mr beams. Roof rafters roof joists and roof beams. Other than plaster or gypsum board.

The attached list of criteria is met. Allowable deflection as an expressed ratio of the clear span. Top running crane trc beams. Therefore a purlin should be adequately strong to withstand the loads it will encounter during its design life and should not sag in an obvious manner thereby giving the roof sheeting an undulating and or unpleasant appearance.

Table r301 7 allowable deflection of structural members. Underhung crane uhc beams. Floor beams floor joists and floor decking. If that same joist had gypsum ceiling l 240 the allowable deflection is 0 6.

For sake of discussion we will assume a minimal roof snow load of 20 psf pounds per square foot and a 4 12 roof slope.