roof design

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I don't know where you'd get a rafter eight metres long.

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Me neither. I'm just telling you what it says in the book...

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Originally Posted by jrock_au

you will have to check your AS but you should be able to join over a point of support but will either have to overlap your two lengths (double check this but I think its 3? times width of timber) or use a nail plate which would be 6? times width of timber. There is also a min fixing rating i.e. 6? Hand driven 75mm nails or 8? machine driven.ffice:office" /><o>:p></o>:p>
hope this helps, sorry I can't be more specific<o>:p></o>:p>

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In my case the rafters were lapped a fair distance, but they wouldn't have to be if you've calculated the spans as a 'single span' as opposed to 'continuaous over two or more spans'.

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I don't know where you'd get a rafter eight metres long

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Hyspan does rafters up to 11.9 metres.

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So your purlins are above your rafters, or are they on top of your roofing

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The purlins are on top of the portal frames and the roofing is on top of them. Of course they don't call them overpurlins, but an underpurlin is so called because it is a purlin that goes under the rafters.

Talk to an Engineer. You can definately splice a rafter if it is at the right location or lap the joint if you provide enough fixing. Best place to lap is about 0.2-0.3x Length.

But do not attempt to do this on your own without professional advice.

AS1684 has been deliberately set up to guide people on what is safe and only experienced professional are allowed to step outside the limits if they can prove that the design is adequate.

That's what I was going to say. If it's not in the framing manual, it's probably still possible but would need an engineer's design to pass.

Ive never heard of overpurlins i was just trying to be funny

Don't give up your day job :wink: