Truss spacing - 600mm centres

[MortarThePoint]

I've had some truss designs from some suppliers and they have all gone with 600mm centres. As I understand it that's the normal way to go these days. Does anyone go for 400mm centres any more?

 

There is a housing estate near us that has lots of slate roofs and they look bad after 5 - 10 years. Not due to the slate, but looks like the underlying timber has shifted over time. We're going for plain clay tiles, but this has made me think about whether too many savings are being made on trusses.

 

It's interesting to see the sizes of timbers chosen by the suppliers for the top chords (i.e. the actual roof slope). One supplier has designed based on 47x147, another used 47x197 and the third used 47x222. There was more agreement over the bottom chords with the same first one going for 47x197 and the other two going for 47x222. The one with the slighter timber wasn't the cheapest either.

[nod]

Nothing to stop you 

But not necessary 

As you say all the designs are 600

[Vijay]

Yep, found the same thing, every supplier was 600 but some varied in depth of timber too

[dangti6]

Which suppliers have you tried?

 

I’m on the lookout at the moment and Pasquill are looking favourable but I’m all ears for more suppliers to approach. 

[Vijay]

Found these guys to be extremely helpful http://www.acrooftrusses.co.uk/  . I haven't ordered yet but unless something comes up, they will be probably be getting my order. Guy I've dealt with is Liam and he's been brilliant!

[MortarThePoint]

In alphabetical order: Donaldson, Pasquill and Truss Form.

 

I've found Pasquill very helpful so am leaning towards them.

 

7 hours ago, nod said:

Nothing to stop you 

But not necessary 

As you say all the designs are 600

So 400mm is a thing of the past then?

[MortarThePoint]

Sorry for the delayed responses, I was busy on site achieving nothing ??

[nod]

52 minutes ago, MortarThePoint said:

Sorry for the delayed responses, I was busy on site achieving nothing ??

That brings back memories ?

[Faz]

Mine designed at 600mm centers - can't see a problem tbf and we get the wind ripping across the Fen!

 

 

[Oz07]

Have trusses ever been at 400 centres or are you referring to rafters?

 

I bet it's more common than you think people using 19mm batten with 60p centre spacing which would likely cause a roof to look bumpy. 

[Gus Potter]

Sometimes, if you have no sheeting (sarking / ply) on the top of the rafters then if the roof is fairly big you want to fix wind bracing to the underside of the rafters. If you have a roof that can say get some snow drift off a higher roof this inceases the load locally. To make this work you decrease the spacing of the trusses where the higher loads are. This way you keep the rafters the same depth and it makes it easier to fix the wind bracing as the underside of all the rafters are in the same plane.