How to replace wood purlin?

[Ady88]

Hello! I am looking to replace a purlin in my roof because the purlin is in two lengths and is supported by a prop at the point of overlap.

I want to replace it with a single length of timber which does not need a prop underneath it.

The span between gable wall end and party wall is 4900mm. What size purlin would I need in timber/steel? Are there any span tables available?
The ground floor is 6700x4900 to give you an idea of the roof size. The other side of the roof was built the same but has been replaced with a dormer and a new structure altogether.

Can anyone offer any guidance please? (I did read through some forums but could not find the exact information I need)

A photo is attached below.

Thanks!!

 

[catlad]

For a slate roof they used to use 9x3" purlins but all roofs are different some have two purlins a side.

 

[noseall]

Can anyone offer any guidance please? (I did read through some forums but could not find the exact information I need)

You are unlikely to get info' that will say "one size fits all".
There are many contributing factors that need to be thrown into the hat, jumbled around, before the hey presto moment can occur.

My guess is that an un-supported (clear) span timber purlin will be untenable. You will likely be looking at steel.

We put a pair in a roof recently that would make your eyes water.

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• noseall
• 14 May 2015
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• noseall
• 14 May 2015
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• noseall
• 15 May 2015
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[ajstoneservices]

I replaced one like that a couple of years ago with a ply box purlin.

 

[Ady88]

Thanks for the replies, the roof did have a purlin each side of the pitch and I'm looking to replace one of them. Those steel beams are huge! @noseall. And the span is only abit longer than my house so perhaps mine will also be fairly deep. I have a steel beam which is 150x150 and that is supporting the new flat roof former so maybe my steel beam to act as a purlin could be of similar dimensions, I will have to ask a structural engineer.

Do you have a link for ply box purlins info? @ajstoneservices

 

[noseall]

Thanks for the replies, the roof did have a purlin each side of the pitch and I'm looking to replace one of them. Those steel beams are huge!

I think there was a cock-up. The SE assumed the span was 8m.

 

[Ady88]

Ah that makes sense..

 

[noseall]

I replaced one like that a couple of years ago with a ply box purlin.

What does it consist of? Did you make it yourself? What was the clear span?
Curious as I have not come across one.

 

[catlad]

I recon that size steel nose would go 18 mtrs never mind 8 mtrs.

 

[tony1851]

@ Nose - you showed us those purlins a little while ago, and their bloated size drew much attention.
If the SE made such a simple cock-up, did she(?) offer to recompense the client for the additional (unnecessary) expense!?

@op a 152x152 steel may well do, though deflection might be an issue depending on the load.
How would you get the steel up there?

 

[noseall]

If the SE made such a simple cock-up, did she(?) offer to recompense the client for the additional (unnecessary) expense!?

I don't think it has ever been brought to her attention. The architect (who allocated this SE) laughed it off. So, I don't know whether he made the mistake or her (the SE). Either way, he's not very forthcoming.

 

[Ady88]

@tony I am currently removing the subfloor to lower it and install a new layout for the staircase so access wouldn't be an issue. I'm going to speak to a SE and see what he/she comes up with!