The tables below give maximum spans for rafters and beams.
Flat roof purlin spacing.
Of course how many trusses a purlin spans over must be considered as it alters their moment and shear diagrams.
End purlins and periphery of roof to be fixed every 2nd crest.
Wider panels allow for greater spacing between rafters.
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.
8 x section modulus of a 4 2 of 1 3125 x fb fiberstress in bending x 1 15 duration of load x 1 15 cr repetitive member factor as the purlins are spaced 24 o c.
But the tables that follow are a lot more specific.
Dead load will be the actual weight of the roof steel and the roof purlins.
Note compliance with e2 as1 is dependent on purlin spacing and gauge of roofing.
The figures are based on quality materials.
In the order shown above purlins laying flat use 2 20d ring shank nails per connection for trusses with minimal spacing hung purlins for wide span trusses lu26 hangers for 2 6 lu28 hangers for 2 8 etc and purlins on edge overlapped not butted for mid range to wide span trusses 8 or 9 spacings installed with 1 60d.
In areas with mild climates patio roofs are generally designed for loads of 30 psf pounds per square foot.
C3 fix side laps and miss 2 hit 1 miss 3 hit 1 miss 2 etc with approved fasteners alone.
To determine how far apart to set rafters measure the width of the metal panel and then the width of the first hill and valley of the panel.
The spacing between rafters in a given building is part of the engineering calculations that determine the required structure of the roof.
End purlins and periphery of roof to be fixed every 2nd crest.
For heavy roofs or in areas with substantial snowfall or winds call your local building department for code requirements.
Or less x 1 1 cfu the flat use factor for applying the load to the wide face of a member.
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.
You can solve them as simpl.
When constructing a roof framework the rule of thumb is that any purlin should have a minimum nominal depth and width of 76 mm or 50 mm and max centre to centre spacing between the purlins ought to be 1 2 m.
With approved fasteners alone.
In the valleys due to the angle typically produced at the valley and the use of transition flashing it is essential that the purlins are doubled in the valleys that is two purlins.
Joints between purlins next to one another should be staggered.
A metal roof must also allow for some overlap on each side of the panels which will reduce the effective width of the panel.
Doubling up in the valleys refer to the installation manual for the proper on center spacing and be sure that the purlin is attached to the roofing truss.
