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Old 03-08-2021, 02:29 PM
Polock Polock is offline
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Default Maximum clear span distance questions

I came into a decent amount of 3in 5lb channel iron and am going to use it to put together a little shed in my back yard. Just a simple slant roof, nothing fancy. Big enough to store the mower and tools and if need be could pull the mower out and pull the truck inside out of the sun/rain/wind/cold to work on it if I need to. Hoping to be able to clear span 15ft across the width, am planning 15×20 but will put a post at 10ft in the center of the side walls. Wondering if anyone could tell me what the maximum distance I could span across the roof is. I have searched quite a bit looking for information on this and haven't found any. Was thinking 5 pieces total with 5 ft between front to back, basically using it like perlin.

It has been many moons since I built hay barns in my summers off from school and I can't recall if 6in or 8in perlin was required to span 20ft between trusses and either way I am not sure how this compares in load strength. I would weld something between them to prevent horizontal flex.

I almost feel guilty using it as perlin and know it will be a pain pre drilling all the screw holes but the price was right because it was free. Any information would be appreciated.
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Old 03-08-2021, 02:43 PM
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milomilo milomilo is offline
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Welcome to the pile. Some structural ace will come along and answer your question.
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Old 03-09-2021, 04:04 AM
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JohnBoy JohnBoy is offline
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Channel isnt something I work with much, but my first question is does it sag any amount when placed on two blocks 15 feet apart?

I've sketched what I think you're proposing with the channels across as purlins.

how much is a decent amount?


If you had enough of it spare you could fabricate a lattice beam to go across the front of the opening, and then fabricate a truss in the middle of the shed from front to back.

This would eliminate any sagging concerns, but would be heavy in itself and would probably require doubling up at the two front pillars, and a double for the pillar at the back carrying the end of the truss.


Just a thought and maybe irrelevant if it's rigid enough, just 3 inches doesnt seem much to me.


But someone who actually knows what they're talking about will be along shortly
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Old 03-09-2021, 09:47 AM
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greywynd greywynd is offline
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Default Maximum clear span distance questions

Well, all I can add at this point is that, with your location saying central Texas, no real worries about significant snowload.

Wind and rain would be the issues. Are you planning on enclosing the walls, or simply a riof to keep the sun and rain off things?

Since you mentioned getting the truck in it, maybe think about going a bit narrower to reduce span, but go longer? So instead of 15x20, maybe 12x24, or 12x30? This would still allow storage at the end with enough length for the truck as needed. And with that, adding in another post or two along the walls for extra stiffening and anchoring from wind? Food for thought.

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Old 03-11-2021, 08:21 AM
bunkclimber bunkclimber is offline
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I'm not a structural engineer but then again you didnt ask for one,but yes you can go 15-20ft no issue with 3"c-channel turned up on edge(not flat) with a no-snow-no roof load situation,with minimal deflection..run and fasten 2x4 lengthwise and zip screw your 36"w roofing metal to those.
I'd use a 3"channel member every 5-6ft apart with the conditions above.


Quote:
Originally Posted by Polock View Post
Wondering if anyone could tell me what the maximum distance I could span across the roof is. I have searched quite a bit looking for information on this and haven't found any. Was thinking 5 pieces total with 5 ft between front to back, basically using it like perlin.
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Old 03-11-2021, 08:26 PM
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arizonian arizonian is online now
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Do you have enough to stack 2 channels in a Z configuration and stitch weld them together to get 6" edge to edge?

One beam high, one beam low running the long way made with 2 channels Z'd together, then purlins across the short span.





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Old 03-11-2021, 11:03 PM
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milomilo milomilo is offline
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I would do like bunkclimber says. His recommendation is the same as what I was thinking. I would run the 2x4 flat lengthwise and at 3' centers for the roofing tin.
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