Pole Barn Truss Spacing

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What do you mean they aren’t 2 feet apart?

Back in the day (early 1990’s) I was on the National Frame Builders Association (NFBA) Board of Directors. One of my fellow board members from the Midwest wanted to take a peek at how pole barns were constructed in the West, so I invited him out for a tour.

After spending a day looking at several of our building projects, his comment to me was, “The inspectors in our area would never let a pole building be constructed with roof trusses placed every 12 feet”.

Twenty years later, I beg to differ. Hansen Buildings has buildings in each of the 50 states and all of them have roof trusses on what my board member friend would describe as being “widely spaced”.

Modern truss design is highly computerized. Enter the span of the truss, bay spacing and load conditions and the engineering programs will design a truss which will meet the design criteria. The lumber and steel plates the trusses are constructed from, have no idea how far apart they are going to be placed.  They are inanimate! Yet, somewhere in the deep, dark reaches of history, lies the theory wood trusses must be spaced no more than 24” on center, or maybe 48”, or perhaps even eight or ten feet? The reality is, there is no magic number.

Framed Pole Barn

36' long garage with 12' bays

While H. Howard Doane is credited with being the innovator of the modern pole barn, it was his Agricultural Service farm manager, Bernon Perkins, who is credited with refining the evolution of the modern pole building to a long-lasting structure.  It was Perkins who pioneered roof purlins being placed on edge. With this design change, roof trusses could be placed 12 feet apart, making it possible for roofs to support the loads to which they would be subjected.

I’ve had roof truss manufacturers try to convince me it is impossible to place wood trusses at spacings of over every 4 feet. Their defense is, “Our engineers will not allow us to”. The manufacturers of the steel roof truss plates (also referred to as gussets or Gang-nails), provide the engineering design for pre-fabricated wood trusses. Their programs will allow for trusses to be placed on 12 foot or even 16 foot centers, and their engineers will place their engineer’s seal on the drawings to verify.

The practicality, cost effectiveness and ease of construction of pole buildings is based upon efficient use of the fewest amount of materials, to do the most work, within safe engineering design. Hundreds of thousands of pole barns are in use today with trusses spaced every 12 feet, or even more. They stand as a tribute to the ingenuity of modern pole building design.

12 Comments

  1. Donald Brinegar says:

    Everything is very open with a clear explanation of issues. Your website is very useful. Thanks for sharing.

  2. Eliz Gallien says:

    Sometimes things just require a lot of effort, time, or patience.

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  3. Major Lallo says:

    It’s hard to find knowledgeable people on this topic, but you sound like you know what you are talking about! Thanks

  4. ibm says:

    Everything is very open and very clear explanation of issues. was truly information. Your website is very useful. Thanks for sharing.

  5. Thank you for another essential article. I wish I had your passion for writing!

  6. Raymond Cumberland says:

    I would like to read the articles about “Not just Grandpa”s Barn anymore. I am planning to build a pole barn for hay storage and would like to know your recommendation for truss design, spacing,size material for perlins, post etc. A 4 and 12 pitch is what I think would be sufficent.

    Thanks

    • polebarnguru says:

      Raymond ~

      Thank you, it is hoped the articles are both entertaining and informative. The best answers to your questions come from knowing the specifics of your particular project. What dimensions (width, length and height) work best with your available space, loading equipment and volume of hay to be stored? Will the building be loaded from an end or a side? Where will the building be located geographically? Areas with high wind and/or snow loads are going to impact the design solution. Please feel free to contact a Hansen Buildings designer toll free at (866)200-9657, who can offer you further specific assistance with a practical and affordable design solution.

      Best Regards ~ Mike the Pole Barn Guru

  7. Very helpful web page you have provided to all of us needing to know DIY ers. We live in South Eastern Washington State and are the second owners of a home we bought a few years ago. It came with a 24′ x 36′ pole barn with a corrugated steel roof and a ½” thick plastic insulation blanket on the underside of the metal at ceiling. It is to hot in the summer and to cold in the winter to enjoy, (conveting it into a Mancave). I have added R21 paper backed fiberglass insulation in between the rafters. The 2” x 6” rafters are spaced 24” on center the length of the barn. There are two double trusses @ 7” apart and spaced at 12 foot centers in the middle. I want to cover the rafters and trusses with ½” thick sheetrock, then paint to hide the added insulation and wiring. My question is will the roof support the added load and will I be creating a major problem with mill due and condensation, since there will be no airspace between the metal and sheetrock? Your help would greatly be appreciated.

    • polebarnguru says:

      Emmett ~

      Thank you very much for your kind words.

      Lots of considerations – first (and most important) chances are very good your roof system is not designed to support the weight of drywall. The 2×6 roof purlins, may be able to support the weight from a structural aspect, however they will overly deflect and would likely cause cracks to form at the joints in the drywall. On its own 1/2″ drywall will sag between the roof purlins, it would take at least a 5/8″ thickness.

      Given all of the above, what are your choices? If the insulation has been neatly installed, I’d consider spraying the paper facing and all of the trusses and truss bracing black. This is what more and more of the commercial applications are doing. For looks, wiring could be installed in conduit – to give more of the upscale industrial look.

  8. Chuck Gilbert says:

    Polebarnguru, I am in the preliminary stages of planning a pole barn house. It will be located in eastern PA upon a wooded, gently-to-moderately sloping lot that is moderately rocky. I am planning a frost protected shallow foundation with radiant heated floors and stamped concrete finish. No piers, posts will be anchored to the slab. The house will be 2 full floors (no loft) and 2000 sq. ft +/-. What I want to know is, what is the most cost effective footprint and post spacing to use for this building? I would like to use 30×36. Typical roof pitch, maybe 8/12. I would love to hear your input.

    • PoleBarnGuru says:

      Chuck ~

      You proposed 30′ x 36′ footprint will be very efficient. Columns set every 12′ along the length is the most cost effective, unless you have much wider spans and very heavy roof snow loads – or extreme wind loads.

      While the most typical, common and cost effective roof slope will be 4/12, I personally like the looks of steeper roof slopes with steel roofing.

      Other considerations – 18″ overhangs will be the most bang for your buck and will keep you from having to rip roof panels lengthwise. Also, make sure to use wet set column brackets. We can provide ones which are designed to take the bending loads imposed by the columns.

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