# Forum Home Renovation Roofing  Roof Purlins

## dub3media

I was wondering wether someone could tell me the need for roof purlins 
I am building a roof 3 degree pitch over a deck that is 3.5m out by 6m long, I am using 190 x45 for the bearers and rafters, what is the main difference with using roof purlins (70 x45) and the other method of just noggin it out with no purlins, other than purlins being the faster method, are their any advantages of having purlins. 
I thought maybe the purlin provided the roof with an air gap to prevent condensation.

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## Tools

What you are referring to are battens,not purlins.It boils down to personal preference for the look you want. 
Tools

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## GraemeCook

> What you are referring to are battens,not purlins.It boils down to personal preference for the look you want. 
> Tools

  Purlin is quite correct, although many people now call them battens. 
I am not certain but I suspect that purlin is the British term and batten is american. 
Cheers 
Graeme

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## Tools

Purlins and battens are not synonymous. Purlins are placed on edge and battens are placed on the flat. 
Tools

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## ausdesign

I suppose it comes down to whether its a 70*45 or a 45*70  :Biggrin:

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## Bloss

> I suppose it comes down to whether its a 70*45 or a 45*70

  Love it when the talk gets all technical . . . :Biggrin:

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## autogenous

In a pitched roof Purlins hold up rafters and take toms or props 
Battens sit on top of roof where tiles or tin roof medium are fixed too. 
Metal roofs can have Z Purlins

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## autogenous

_ I am building a roof 3 degree pitch over a deck that is 3.5m out by 6m long, I am using 190 x45 for the bearers and rafters, _ Will the 190mm span 3.5 metres without sagging? The noggins are trimmers 
Really you want rafters that will span 3.5 metres. You can then batten over the top or trim out with lighter material to stop the rafters twisting. 
If you trim out the same centres with the same as the rafter material you will potentially double the weight on the spanning rafters.

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## straight_edge

A batten is a size of timber, like bulk, board  scallion or plank timber!   Purlin and girts relates to steel construction, which can be a z,c or hat section.

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## Tools

Both purlins and roof battens can be either metal or timber. And I am pretty sure that the TFM has seperate tables for roof battens and purlins..  
Tools

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