prefabric truss on flat roof

[Peter louis]

Hi, Guys

How can I tell from the flat roof structure regular joists or pre-fabricated truss? By the span or by age of building?

Thank you

[Matt Fellman]

You could cut a hole in the ceiling :)

That's about all I can think of. You can sometimes grab a glimpse at an exhaust fan or get an idea by how deep a skylight is. Many times I have no idea but don't really worry about it. I just put "unknown" on the report and have never been questioned. Ultimately, we can't be expected to see through the ceiling.

[Robert Foster]

If it's not visible, write "not visible" ....not much good is done by speculating.

[Mark Webb]

This is a structural engineering question.
Best guess is to note the span length between either the columns or the ridge and the exterior wall. You need to know how far each of the framing members are running.
Generally over a certian distance (say 20' or so) It has to be made as a truss assembly or a Glu-Lam to carry the weight. I suppose steel might fall in there too but you can usually tell if its a steel framed building.
So if its wood frame and 25 to 40' it most likely a truss and if 10 to 20' it could be a wood framed in with two-by type lumber.
This is very rough and uses type 5 construction guidelines as its basis.

[Glenn Duxbury]

Hi, ALL &

* Time to utilize 'that' X-Ray vision we're all expected to have (just kidding, of course)...

CHEERS