Flat roof furring spacing

[Moonshine]

To get the fall on our flat roof we are putting on roof furrings.

 

The furrings are running perpendicular to the joists so we can have them at what ever spacing we want.

 

Is 600mm centres standard? I was wondwring about 400mm centres to reduce the chance of the 18mm OSB3 boards sagging but then remembered the 150mm of PIR will add rigidity.

[nod]

600 are fine 

[Gus Potter]

Ah.. but how thick are your firring pieces at the thin end? That is what you need to check first.

 

Be careful here and make sure your builder is not telling you a story or you have not understood how the loads are transferred from the OSB3 to the main joists if DIY.

[saveasteading]

2 hours ago, Gus Potter said:

make sure your builder is not telling you a story

ah, the stories I heard this week about why the level was out, the concrete had cracked and there was an over-order of 3m3!

The last one being so ridiculous I may recount it.

The people are so pleasant and apparently caring that I think it is genuine ignorance. But it is their self-certainty that worries me.....is this the norm in housing trades?

 

Moral....they think they know more than they do....check it out.

[Moonshine]

19 hours ago, Gus Potter said:

Ah.. but how thick are your firring pieces at the thin end? That is what you need to check first.

 

to be determined, what are the implications here?

[Mr Punter]

58 minutes ago, Moonshine said:

to be determined, what are the implications here?

 

I think they should be at least 35mm.  Some of them run down to nothing, which is OK if they are on top the joist parallel but not if perpendicular.