Graphical Construction Glossary >> Roofs and roofing. >> Roof Framing >> steel purlin

Steel purlin
A horizontal roof member to which roofing is fixed.
Mostly cold rolled galvanized steel but can be any steel section thin enough to be easily screwed to.
Rectangular Hollow Section. Often used as purlins on roof to decks and verandahs, where the structure is exposed to view. Usually the wall thickness used is 2.0mm or 2.5mm. Should always have welded end caps to seal the inside from corrosion.
"C", or Cee purlins.
Cold rolled sections in the form of a letter "C". Used not only for roofs but for wall girts and they are used by shed manufactures to form columns, ties and braces. They are also used for floor joists.
"Z" or zed purlins.
Cold rolled sections in the form of a letter "Z". Used mainly in large roofs and as wall girts. Zeds have the ability to overlap at the joints giving them a great strength advantage over the Cee purlins. Also can be used as floor joists.

c and z purlins

zed purlins lapped
When Zeds are overlapped at the connections to supports the strength increase is significant.

The advantages of steel as a purlin material over timber are obvious.

  • Known properties. The products are or a consistent quality and the engineering properties are well known and documented. Unlike timber which can vary enormously in strength etc.
  • Long lengths are available, up to the maximum allowed for road transport. 12M. lengths are common.
  • Ease of use and fixing. Roll formed purlin can be ordered with the bolt slots pre-punched.
  • Cee and Zed purlins can be ordered cut to exact length so allowance for waste is zero.

It should be noted here that laminated timber engineered beams are also available in long lengths, but they are too deep in section to be even considered as over purlins for directly fixing sheeting to. Support purlins yes.

Cee and Zed purlins come as complete roofing with various accessories to numerous to list here. Purlin bolts, fascia purlins and purlin bridging are.

rhs purlins

The whole of this roof framing for an elevated deck is constructed with RHS material, including the steel purlins. Note that the ends have been capped.

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Please Note! The information on this site is offered as a guide only!  When we are talking about areas where building regulations or safety regulations could exist,the information here could be wrong for your area.  It could be out of date!  Regulations breed faster than rabbits!
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