Typical attachment method(s) for steel trusses?

[william]

Hi, this is my first time coming across such roof, so I thought I'd ask here first. An engineering is looking at the case as well, but in the mean time I just wanted to get a rough idea of what the standard practice would be for steel truss roofs.

Roof specs:
Asphalt shingles -- plywood sheathing -- cold formed steel trusses 2' OC.
6/12 pitch

Lag the L-brackets down with self-tapping bolts through the truss?
Or drill the truss and bolt/washer/nut? (Seems tough given limited access to the attic.)
Or a lot of L-brackets on the sheathing without consideration of the trusses?
Or other methods?

Thanks a lot for the help.

[inetdog]

Hi, this is my first time coming across such roof, so I thought I'd ask here first. An engineering is looking at the case as well, but in the mean time I just wanted to get a rough idea of what the standard practice would be for steel truss roofs.

Roof specs:
Asphalt shingles -- plywood sheathing -- cold formed steel trusses 2' OC.
6/12 pitch

Lag the L-brackets down with self-tapping bolts through the truss?
Or drill the truss and bolt/washer/nut? (Seems tough given limited access to the attic.)
Or a lot of L-brackets on the sheathing without consideration of the trusses?
Or other methods?

Thanks a lot for the help.

Not having worked with steel trusses, and given that there may have been a reason for using them (high loading, for example) I would be reluctant to drill anything into them without finding out more about the manufacturer's recommendations regarding attachments. Among other things you do not want the holes to provide a starting point for stress cracks.
Without some confirmation that it is OK, I would be tempted to clamp to them rather than drilling. Or to run a backing rail behind/underneath the truss members and attach to that.

How is the sheathing attached to the trusses? That may give you a good idea how to proceed.

Definitely a good idea to involve an engineer!

[william]

Not having worked with steel trusses, and given that there may have been a reason for using them (high loading, for example) I would be reluctant to drill anything into them without finding out more about the manufacturer's recommendations regarding attachments. Among other things you do not want the holes to provide a starting point for stress cracks.
Without some confirmation that it is OK, I would be tempted to clamp to them rather than drilling. Or to run a backing rail behind/underneath the truss members and attach to that.

How is the sheathing attached to the trusses? That may give you a good idea how to proceed.

Definitely a good idea to involve an engineer!

That's a great point! I'll investigate that. And oh yes, I wouldn't dare do anything without an Engineer's guidance at the absolute least.

Thanks for your response!