Pole barn roof question

[jml755]

Marginal? Anything but. It is no better or worse then a 2x4 on 8' center. Both 2x4 on 8' and 2x6 on 12' are a "simple solution that is well documented as acceptable pole barn design".
I never implied that his truss couldn't set on a header. Insisting that he can't have a 12' span is even less helpful. Must be one of these I have never seen or done it so it can't be done.

:laughing: No need to get snotty, I'm not "I]I have never seen or done it so it can't be done[/I]" I'm one of those "design to engineered standards" and when I said "marginal", I was citing figures from actual span tables for joists/rafters with the lightest loads listed. Here's a link to one of many: "http://wclib.com/pdfs/SimpSpanTbls.pdf". I don't know of any tables for "purlins" but looking at the rafter and joist spans for 2x6's on 24"o.c. will give anyone an idea at what a particular dimensional piece will support. Note that it varies depending upon grade of lumber AND the anticipated loading. With purlins and rafters, snow loads are probably the biggest consideration since they don't see higher "live" loading like a joist. There are conditions where a 2x6 will span 12' but I see those to be using "select structural" lumber. Here in Michigan most of our stuff is simply SPF so I use those columns.

 

[Duffster]

:laughing: No need to get snotty, I'm not "I]I have never seen or done it so it can't be done[/I]" I'm one of those "design to engineered standards" and when I said "marginal", I was citing figures from actual span tables for joists/rafters with the lightest loads listed. Here's a link to one of many: " http://wclib.com/pdfs/SimpSpanTbls.pdf ". I don't know of any tables for "purlins" but looking at the rafter and joist spans for 2x6's on 24"o.c. will give anyone an idea at what a particular dimensional piece will support. Note that it varies depending upon grade of lumber AND the anticipated loading. With purlins and rafters, snow loads are probably the biggest consideration since they don't see higher "live" loading like a joist. There are conditions where a 2x6 will span 12' but I see those to be using "select structural" lumber. Here in Michigan most of our stuff is simply SPF so I use those columns.

I got news for ya. A post frame building roof purlin is not a joist nor rafter. Try looking up some tables for post frame construction.

You also seem to be ignoring wether or not it is a simple or compound span.

A 2x4 for a roof purlin with trusses 8' o.c. is an industry norm. 2x6s are rated the same for 12' centers. I use SYP but WW will work fine. I would certainly hope that doug fir is readily available as well.

 

[mfairbank]

So it sounds like the best idea for me to do is to stack 2x6s on edge on top of the trusses instead of using purlin hangars. I just worried about walkin on top of them 2x6's i would think they wouldnt be as stable. For when i putting the barrier material and the metal down for the roof