pole barn questions

   / pole barn questions #1  

aj1

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Oct 15, 2009
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i am planing to build a w16xL40xh12 pole barn over my camper and slowly finish it in to a house over time then pull the camper out. im going to use 4x4 post 8' o/c. i think i can go with a 16 foot span useing 2x6x16 joist and 2x4purlins? i dont know if i should put the purlins and joist 2'o/c or 16"o/c? i want to use 3/4 ply wood decking with shingles or maybe i should use 2x8 joist but im on a buget. i just dont want my roof to sag i live in south east texas. no snow im not going to put a lot of slope to the roof. i will have shingles and ply wood on top and later sheet rook on the joist and maybe some a/c duck later. i know that 2x6 will work 2foot o/c with a 16 foot span useing only tin but im going to have decking shingles and later sheet rock. i may have to suthern enginer some trusses lol after all i am a field enginers helper i do basic lay out and off set lines for hi rise buildings should have been a structural enginers helper lol.
 
   / pole barn questions #2  
I think you should consider a larger post instead of a 4x4. You need to consider wind load on your sidewall. Being 12' and spanning 8' between, I would go with a 6 by at least unless it will be in an area that isn't exposed to any wind.
 
   / pole barn questions #3  
3/4" roof decking????
Try thinking 7/16" OSB
 
   / pole barn questions #4  
3/4" roof decking????
Try thinking 7/16" OSB

I would definitely, definitely NOT use 7/16" OSB. I've seen it used under shingles several times, and after a couple years it always sags and droops under the weight, even at 16" OC. You can stand back away from the roof and easily see where every single rafter or truss is underneath by the way it sags in between. Maybe bobodu has had better luck with it, but I'd spend the little bit extra to get 3/4" T&G OSB. It's about double the price of 7/16", but about half the price of 3/4" plywood. For 20 sheets total, which is what your building should require, you'd be talking about roughly $100 for 7/16" OSB, $200 for 3/4" OSB, and $400 for 3/4" plywood.

As far as the rafters go, if you want to withstand 10 psf live load and 10 psf dead load (the absolute bare minimum IMO), you'll need to use select structural grade 2x6's to make that span, whereas you could get away with No. 1 or No. 2 grade 2x8's. My guess is that #2 2x8s will be your cheapest option.

For posts, I'll definitely agree that 4x4's are too small for a 12' height. If you can't afford 6x6's (and they certainly are a lot more expensive), at least go with 4x6's.

Good luck.
 
   / pole barn questions #5  
Stay away from the OSB or 3 ply plywood for the roof. Use 1/2" 4 ply or better yet 5/8" plywood.
Consider three 2X6's bolted together for your posts.
 
   / pole barn questions #6  
definitely go with laminated 2X6 or 8 for the posts. Laminated posts of that size are not only much stronger, but laminated posts will not twist over time as a single post will. The first barn pole building I put up had 8X8's treated and they twisted I bet 10 degrees in spots.
 
   / pole barn questions #7  
I recommend you go to a lumber yard and see if they have pole barn designs to review. It would give you some more ideas. I agree with laminated 2x6 poles, the bottoms are made from treated lumber and they transition to untreated above the ground.

For purlins, 2x4 would work but they probably will sag in the middle over time and weaken at the ends. If your going to live in this, I would go with 2x6 purlins. Sure you're on a budget but some investment now will pay off down the road. I would also be concerned about a seam in your structure at each pole. Try to get 16 footers and stagger your joints.

Sounds like your are raftering this instead of engineered trusses. If so, you'll need a ridgeboard...don't just try to nail rafters to each other at the peak.
 
   / pole barn questions #8  
i am planing to build a w16xL40xh12 pole barn over my camper and slowly finish it in to a house over time then pull the camper out. im going to use 4x4 post 8' o/c. i think i can go with a 16 foot span useing 2x6x16 joist and 2x4purlins? i dont know if i should put the purlins and joist 2'o/c or 16"o/c? i want to use 3/4 ply wood decking with shingles or maybe i should use 2x8 joist but im on a buget. i just dont want my roof to sag i live in south east texas. no snow im not going to put a lot of slope to the roof. i will have shingles and ply wood on top and later sheet rook on the joist and maybe some a/c duck later. i know that 2x6 will work 2foot o/c with a 16 foot span useing only tin but im going to have decking shingles and later sheet rock. i may have to suthern enginer some trusses lol after all i am a field enginers helper i do basic lay out and off set lines for hi rise buildings should have been a structural enginers helper lol.

16' wide isn't enough for a house - make it 24' wide
Use 6x6 posts
Use 2x8 rafters 16" OC and 5/8" plywood with clips - you don't need purlins
You can use 2x4 for ceiling joists - use 2x6 if you ever plan to add insulation
2x4 roof trusses will work fine too

An extra $500 in lumber at the beginning and you'll have a building you can actually keep standing for 100 years.

JayC
 
   / pole barn questions #9  
When I said purlins, I meant girts. I get them mixed up. Purlins are stringers on roofs, girts are horizontal stringers on walls. You'll need girts but not purlins.
 
   / pole barn questions
  • Thread Starter
#10  
ya im not going to use osb of any kind. im going to see if the 1/2in plywood is cheeper than 3/4 that sounds good to me. so 4 2x6 boards bolted together is stonger than 6x6 post? that will be cheeper any way ill bolt them together every 2 foot. i dont think the purlins will weakin on the ends im only going to have 1' 6" over hang i see lots of old homes with 2x4 purlins. im going to use a ridge board and a 2x4 from the ridge doard to the ceiling joist that should keep it from saging in the middle right? the 24x24 sounds good i just dont have the money for that now and i need the foof fast i can allways add on later. now the haveing to use 2x8 or hi dallar 2x6 sucks but ill look in to that. i dont want it to sag or move around and crack all my siding and sheet rook later. thats my new plan what yall think ? i would realy like to use plane old 2x6 joist if i can?
 

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