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I have an old barn with a up stairs and down stairs. Im looking to replace the floor joists that are broke. The joists are actual trees that are trimed to fit. They are probably 10" diameter with no post support between the span. The span is 25 feet.. The joist between eachother is about 3 feet. What would be the best replacement and what would carry 1 to 2 ton. Thanks.

  • As you might expect from them being broken, 10" diameter on 3 foot centers spanning 25 feet is not a particularly good design to begin with, weight-capacity-wise. Being subject to the inherent drying defects of whole trees only makes them worse. – Ecnerwal Nov 13 '16 at 21:03
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While you do not have enough loading information to give a more exact answer, you could typically use taller and/or larger flange I-joist or 4x2 floor trusses. The key is height to whatever you put in.

I-joist can easily give you the span you need, its just a matter of loading.

For comparable cost at longer spans and higher loadings, floor trusses can pretty much do what ever you want if you give them enough height. Just locate a truss company and meet with them and they should be able to guide you on a proper truss design and get you a quote.

For a barn, I would probably go with I-joist but if you need to run any mechanical or plumbing, I would recommend floor trusses.

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    Yes, but conventional residential and light commercial floor trusses aren't commonly asked to carry stacks of hay. ;) – isherwood Nov 11 '16 at 14:10
  • Floor trusses will hold whatever they are designed for. A design we had a couple years ago had 150 psf storage loading @ aprox 20' span. That is 6,000 lb per truss design load. I'm just not seeing a problem. – Damon Nov 11 '16 at 16:57
  • True again, but an ancient barn isn't the most stable of environments. I'm not sure any manufacturer would approve wooden trusses for such an application. Don't mean to be argumentative, but conditions are much less controlled in an old barn. I'd want steel or solid wood. – isherwood Nov 11 '16 at 17:01
  • If conditions are acceptable for LVL, then the conditions are acceptable for floor trusses and joist. Age of the barn is irrelevant to design and use of a truss or joist. Weight is weight; bearing is bearing. And if cost and complexity are no issue, then of course steel is a great choice. If possible, I would use a floor truss over LVL any day due to simplicity, strength, and cost. – Damon Nov 11 '16 at 17:14
  • Trusses are used in barns all the time; they are used so much they even have a unofficial term for them: AG Truss. If an old barn stays dry, then our truss manufacturer will build what ever we need. They have never given us any disclaimers for trusses we have used in barns. – Damon Nov 11 '16 at 17:26
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The only acceptable modern option to span 25 feet, especially at that wide interval, will be steel I-beams or trusses, or engineered lumber (LVL) beams. Consult an engineer with your exact specifications. He or she will probably want to do a site visit.

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