Roof Rafters
Roof Rafters
(OP)
Not sure on this, been a while for wood design. Does code require that roof rafters have blocking between them? I saw a building with looked like 2x12 rafters, no blocking at all. Did have hurricane hold downs, so this was the roof.






RE: Roof Rafters
Garth Dreger PE
AZ Phoenix area
RE: Roof Rafters
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Roof Rafters
The roof truss installer may install blocking if it helps keep the structure stable during erection.
I wouldn't be bothered going to site and not seeing blocking between the rafters unless it was specifically detailed.
RE: Roof Rafters
RE: Roof Rafters
Mike McCann
MMC Engineering
Motto: KISS
Motivation: Don't ask
RE: Roof Rafters
RE: Roof Rafters
If it is a very shallow roof framing member, there are mechanical connectors capable of resisting this in-wall-plane shear force, but none that I know of for 2x12s. Or diagonal straps/braces depending on the force. But you have to check the numbers.
My answer is blocking, almost always does the job, cheap, hard to mess up. Yes you have to coordinate ventilation. There was a multi-page article a few months ago in Structural Design or something similar on this very subject, the only one I have ever come across... Yes I am in high wind country but even in low wind country how do these forces get transferred without blocking or diagonal straps?
Andrew Kester, PE
Florida
RE: Roof Rafters
I think above people were refering to a prescriptive method that is allowed. In Florida I think if you go above a certain wind speed prescriptive methods can not be applied. I really could be wrong about this. The way I look at it though is if someone is hiring me to engineer the structure that is what I'm going to do prescriptive method or not.
John Southard, M.S., P.E.
http://www.pdhlibrary.com
RE: Roof Rafters