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Pole Barn Roofing Question

Scott11T

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I am planning out the roof framing for my pole barn. Trusses will be spaced 8 ft apart. With that spacing I'm pretty sure purlins will need to be on edge and not laid flat. I'm wondering if it is ok for me to stagger the purlins in between the rafters and screw through the rafter and into each end of the purlin. This would be instead of using joist hangers.

Any thoughts would be greatly appreciated!
 
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MrSurly

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I would point you to this site as they design similarly and there is a ton of great reference info there. I did not build mine their way but I might build the next one like that.

I don't remember their attachment method, but i don't think it's joist hangers.
 

XRlifer

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I would point you to this site as they design similarly and there is a ton of great reference info there. I did not build mine their way but I might build the next one like that.

I don't remember their attachment method, but i don't think it's joist hangers.

I bought my kit from Hanson, and it came with Simpson LU26 hangers.
 
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Scott11T

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Thank you for the input.

I was thinking staggering like this may be faster and less expensive. I wasn't sure how much stronger using the joist hangers would be. If there is a clear advantage to the joist hangers I don't have a problem using them.
 

MrSurly

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I wince at the thought of even considering staggering the purlins because you're already going to have a terrible time trying to correctly place your screws, just because the purlins are *on EDGE* and then add at they're being staggered will surely lead to a lot of extra holes AND (worse perhaps) the lines of the screws on your roof will reflect the offset. No, thank you.
 

MrSurly

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Thank you for the input.

I was thinking staggering like this may be faster and less expensive. I wasn't sure how much stronger using the joist hangers would be. If there is a clear advantage to the joist hangers I don't have a problem using them.

I would think that the case could be made for using TimberLok type screws as they are astoundingly strong, but they are *MORE* expensive than Simpson Ties.
 

bigdav160

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If you watch this video, I think they've done exactly as the OP is proposing. Doesn't seem to be an issue:

<iframe width="560" height="315" src="https://www.youtube.com/embed/J57gzdYrzUI" frameborder="0" allow="accelerometer; autoplay; encrypted-media; gyroscope; picture-in-picture" allowfullscreen></iframe>

Edit, in a previous episode they pre-drilled the purlins and screwed them to the trusses
 

MrSurly

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If you watch this video, I think they've done exactly as the OP is proposing.
Edit, in a previous episode they pre-drilled the purlins and screwed them to the trusses

Actually that's a bit different, placing the purlins edgeways, but on TOP of the trusses which arguably not as strong or wind-proof as the O.P.'s proposal which would have the purlins 'between' the trusses, with the top edge of the purlins flush with the tops of them. The O.P.'s plan is like the Hansen method which does look very stout.
 
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Scott11T

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I have considered putting them on top but not a fan of toe nailing/screwing. Also afraid of splitting. I’ll have non insulated metal roofing. I’m debating putting the purlins inline and flush with the rafters or staggered and flush with the rafters.

Right now thinking in line with joist hangers might be the best option. Pitch will be 7/12
 

rayra

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They're not toe-nailed in the RR video, they're pre-drilled and nailed clean thru, fully overlapping the truss frame. Just as strong as a hangar and no hangar hardware (expense) needed. It's a pole / post-frame building not an erector set. You can spend as much on hardware as wood, the way you are talking about doing it and not gain much of anything from it.
 

rayra

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Just a reminder that it doesn't make much sense to try and make such a structure rigid or super-strong. Especially if it is only being roofed with sheet metal. You gain nothing by doubling the cost of your purlin setup.
Building is gonna move. The sheet metal is a 'stressed skin' sort of thing, part of the strength of the walls and roof. Doubling your cost and time of install with hangars and butting purlins between your trusses is no stronger than having your purlins run across the top of the trusses. You aren't gaining any snow load rating from doing so, regardless of what some stamped plans say.
If you are building a kit that says 'do it this way or no warranty', that's your choice. But don't think it's better/stronger. The issue is still one of span strength of the dimensional lumber used.
 

readhead

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PD, I’m a metal guy not a wood guy. I would install the purlins flush at the top in hangers. If installed on top of the truss there needs to be some blocking between the purlins so they don’t roll over. ( I actually am a wood guy. Been a GC for thirty five years but don’t spread that around.)
 

MrSurly

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Additional thoughts on this: When I started mine I researched a bunch into what the pole barn/ post frame sellers were selling around here. There is a lot of price competition and they were all essentially the same design, minor variations in lumber specs. I had to recognize that ALL of their designs were spec'ed to be as cheap as they could be reasonably built. I took their design and spec'ed bigger lumber and more fasteners. I then got bids. Then, the city pointed to their requirement for a P.E. stamped drawing... and 130mph wind load ratings and this and that other thing. Reluctantly, I hired a pole barn P.E. and paid him for his approval. He beefed up the build a good bit MORE. When the drawing was finished, all mandates concerning wind loading, deflection, shear walls, footing loads, uplift, purlin fastening/placement were all calculated and set in writing. Yes, I begrudgingly had to pay hundreds for his service, and only because I was forced by the city to do so. But to be honest, I LIKE the fact that I know that a P.E. made the changes, even though it cost me more. I feel GOOD about the beef that was added and the way it's held together. I also didn't have to fight my personal tendency to 'engineer on the fly' making changes that I might doubt later. Is it the route you should go? Maybe, maybe not. I know in my case, I *wouldn't have* done it, but I'm GLAD I did.
 
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