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  1. #1
    Silver Member Coyote's Avatar
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    Default Roof Truss Span

    I want to build a 20' x 40' pole barn, (20 deep and 40 wide), basically I'll have 4 - 10' wide "bays". Anyway, can I span the 20 feet with one truss? I'm thinking about a 24' truss set on poles 20' feet apart to achieve a 2' overhang. Roof will be tin. Make sense?
    Coyote Creek

  2. #2
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    Default Re: Roof Truss Span

    My barn has 40' clear span steel trusses. I see similar type trusses at the local 'barn' store - you may be able to buy them pre-fabbed. They may also have pre-fabbed wood trusses - or look up trusses in the phone book - pre-fab wood trusses are readily available.

  3. #3
    Platinum Member firefighter9208's Avatar
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    Default Re: Roof Truss Span

    I have a 30x40 shop and used wood trusses. I told the truss company that I wanted to span the 30'. They build the trusses for the span and I haven't had a problem the 8 years since the building was built. I say check with they truss company, but it shouldn't be a problem.

    Chris
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  4. #4
    Super Star Member EddieWalker's Avatar
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    Default Re: Roof Truss Span

    Yes, 24 foot long trusses are pretty simple. Are you going to build them yourself, or have them built? Either way, be sure to calculate your design on the 20 foot span from wall to wall. The overhang isn't the important measurement.

    Spacing your trusses for a metal roof will decide how many you have. I like to put them in on 4 foot centers, then use 2x4 purlins on there flat side. This makes them easy to attach and easier to find when attaching the metal panels.

    You can go to 6 foot centers with 2x4's on edge, or 8 foot centers with 2x6's on edge. Spacing of the purlins is something you need to check first with your metal supplier. I like them every four feet.

    What pitch are you going to use? 4:12 is what I like as it's steep enough too look nice, but not too steep to walk on. Even at that pitch, you have to have clean, white soled sneakers to walk on it. Dark soled shoes are harder and more slippery. Any dust at all will cause you to slide off the metal at a 4:12 pitch. If you go steeper, it just gets allot harder, to impossible to walk on it and do any work. I did one roof at 5:12 that was the absolute max that I could crawl up and down. Even then, I had more close calls then I want to remember.

    Do you get snow? If so, ignore everything I've said as it doesn't apply to snow loads. For snow, you need an engineer to tell you how much load you can handle and how to design the roof.

    Are you limited in size for your building? Will you have doors in your four bays? If so, then ten foot is kind of tight. I'd go 12 foot for each bay, and make the doors ten foot wide. That extra 8 feet in lenght isn't going to add very much to the overall cost of the project, but the extra space will be appreciated for the life of the building.

    Eddie

  5. #5
    Silver Member Coyote's Avatar
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    Default Re: Roof Truss Span

    Thanks for the expert advice, I am torn between a simple shed type roof, (10' high in front; 8' high rear) or trusses. This is a do-it-yourself job, except I would have the trusses made. Either way I haven't prepared the pad yet so I'm still in design mode! Eddie, your detailed answers are amazingly helpful! Thanks again.
    Coyote Creek

  6. #6
    Gold Member dtd24's Avatar
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    Default Re: Roof Truss Span

    We built an office building that had a 60' span.
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  7. #7
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    Default Re: Roof Truss Span

    We're getting ready to build a shop with a 30' span with trusses, I don't know how far you can go but our building code will only allow 36' clearspan for wood trusses. After reading a ton of pole barn threads (and as Eddie mentioned)- we will go with wider bays to allow for 12' wide doors- should keep me from hitting anything with the bush hog attatched.

  8. #8
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    Default Re: Roof Truss Span

    These on my roof are 50 foot span with proper enginering anything can be done
    50 foot over wall with a 2 foot overhang



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  9. #9
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    Default Re: Roof Truss Span

    I would take earlier advice and have the truss company engineer them for you. They have software that will tell you how long you need to go with the span. Even with metal ceilings I disagree with eddie a bit I would go on 2 foot centers. My garage is spanning 28 feet and my truss builder said I could go with 24 inch centers if I was useing metal. I went with 16 inch centers because I liked the extra strength. You might want to look at a website. Adams Truss, Inc. - Engineered Steel Building Trusses and see what their prices are on just the steel trusses. They are built on a ten foot center.

  10. #10
    Super Member flusher's Avatar
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    Default Re: Roof Truss Span

    Quote Originally Posted by Coyote
    I want to build a 20' x 40' pole barn, (20 deep and 40 wide), basically I'll have 4 - 10' wide "bays". Anyway, can I span the 20 feet with one truss? I'm thinking about a 24' truss set on poles 20' feet apart to achieve a 2' overhang. Roof will be tin. Make sense?
    Don't know if you need a building permit in your county for your pole barn.

    Some counties require trusses to be engineered and the truss design package has to accompany the application for the building permit.

    Also, some counties require that the trusses be fabricated by a licensed manufacturer.

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