Roof: box section on OSB on steel purlins.

[Chris Bacon]

The intent is to sheath the steelwork of the roof with OSB or similar, and go on that with 34/1000 box profile.

Roof pic:

It might be possible to screw straight through the box profile and OSB into the steel purlins with TEK-3 screws, but there's scope for missing the target, which would be unfortunate. The purlins are equal angle

40x40x3mm mild steel, about 1000mm between the trusses, purlin apacing each side about 1150mm.

I could secure OSB onto the steelwork, and mark out the purlins' positions on that I suppose. I could secure the OSB onto the purlins/trusses and fasten the box profile to the OSB only. Hm.

Any suggestions as to how to approach the job?

[fred]

Could you not mark up the purlin position and pre drill the holes. Beside which when you lay up a sheet the positions of the purlin will be visible at one end making it easy to eyeball the screw position

[Tricky Dicky]

I think I would attach some battens to the angle something like 2? X 2? square then you have something more to aim at when sheathing with OSB. What I would advise against is any drilling of the vertical part of the angle iron as that is where the strength is.

Richard

[Tim Lamb]

In message <sa9scb$15nk$ [e-mail]>, Chris Bacon [e-mail] writes

Hmm.. I'm no structural engineer but I suspect that frame is a bit light on snow loading.

You could mark the purlin positions as you fit the OSB although the fixings would perhaps be enough indication. Box section roofing is normally secured through the valley section and relies on sealing washers for weather proofing. Worth hiring a TEK screw driver if you don't have one. There may be an issue with the threaded screw section engaging and lifting the OSB while drilling the purlin. You need to use butyl strip to seal the weather lap and TEK together at the recommended spacing.

[Chris Bacon]

Frame? The trusses? How so?

I'll think about that and other ideas. When the materials are here I'll have something physical to fart about with. That will probably be helpful, having the stuff on site.

[Tim Lamb]

An agricultural building with 15 foot bays and 12.5 deg. slope would have 7" Z purlins spaced at 1.4m apart. Your structure appears to have significantly less than that

[Chris Bacon]

No, it's not. It's a conversion job from an old double garage.