There are people who don’t know that their grammar is so bad they’re hard to understand.
It’s not so hard to use each word in its correct place.
To get to the OP's question,
I have built several pole barns. I generally do 24 OC spacing, but I am also a conservative builder. The only issue I see with the spacing is that with the 2x4 on flat with the 4 ft OC spacing is that they will sag and it will make it "interesting" if you have to get on the roof for any reason. At a minimum, I would recommend turning the 2 x 4 on end.
Just to make a general argument, if you switch to 24 OC for your trusses, you will have a building that will last for 50 years or more and added the costs are not significant.
My pole barn has 8 foot centers and it is 30 years old and still looks new. We do get a lot of snow here also as I am in the snow belt.
I think some of the comments indicate no knowledge of pole buildings. Now on to the original question. I'm not saying Morton won't use 4' spacing but that would be based on the customer's insistence. Maybe in ultra high snow load areas. Here we get snow but nothing like northern Michigan or Wisconsin/Minnesota. My building has them 8' on center. We had 16" in one snow last winter with no issues. I went with perma column posts. That's precast concrete in the base and the truss sandwiched between laminated posts. Here's a link for them. You will notice the photos show probably 8' spacing's.
https://www.permacolumn.com/
Last edited by Ronald Blue; 09-08-2019 at 3:51 PM.
http://www.southernpine.com/span-tables/joists-rafters/
This site will help.