Pole building construction is one of the world’s oldest construction techniques. Savings on the foundation, minimal disruption to the building site, and the ability to build on slopes or other difficult terrain give these buildings an advantage over others. I pulled out my documentation and notes that we used for our home, dusted them off (cough cough) and share more design details here.
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Framing Differences
When it comes to framing in your pole building, you have a flexible and straight forward task. In a pole building, all the structural design and construction is complete before you’re ready to add walls. I like to think of it as, ” let’s add walls to keep the wind out”. You see, in a pole building, walls don’t hold up the roof at all! Its the poles and beams that support the roof. In the future, if you want to add a window, or door, or other opening, its easy
When using traditional platform framing methods, the walls are, “load bearing”. They support the roof, so each time a window or door is framed in, extra lumber and calculations are made for the door or window header design.
Design Approach
The approach I took in doing a pole building was to start with the roof and move to the floor and pole loads. This way, if the pole loads were too high, I could modify their number or placement without too much recalculation for other parts of the building.
You will want to check with local builders and codes to determine what roof load your building must support. Think of the worst snow load turning to heavy slush. Sure, the roof is probably slanted, but you definitely want a safety margin with the roof load number.
In a rectangular building there will be two parallel beams fastened to the tops of the poles. You multiply your roof load factor times the square feet of the top of the rectangle. This calculation is the same whether you order trusses like I did, or frame your roof. This gives the theoretical maximum load that could be applied to the building. Divide this total by two and then divide it by the length on one of the 2 roof support beams. This is the pounds per linear foot that the roof beams must support.
Now that we have the load on the roof beams, we need to make sure that we have the right lumber between poles to support the load. There are standard lumber and load tables given in the Seddon book referenced below which give the total load that is safe for standard lumber. For example, 2×8 inch beam that spans 10′ between ends can safely support 1051 pounds of load. That would be an average of 105 pounds per linear foot.
For a framed floor there will be another set of parallel beams attached to the poles. The calculations here are quite similar to those for the roof load. I used 50 lb per square foot for my floor load, however, it the area where I planned for batteries, I doubled that to accommodate the extra weight.
Finally you’ll want to consult the section of the book on pole loads, and soil types to make sure the total load on any given pole is within an acceptable range. We used treated 6×6 poles, with the longest one being 26 feet. (The second story, is another story) Anyway, that’s the thumbnail sketch of the building design process we went through.
Favorite Design Guide
There are many guides and books out there on the subject of pole buildings since the technique has been around forever. I probably used and compared 3 or 4 books in my research and design phase, however, one stood head and shoulders above the rest.
Practical Pole Building Construction: With Plans for Barns, Cabins, & Outbuildings
Leigh Sheddon’s book was the most practical and complete book I found. My copy is dog eared and dusty, but always a good reference to have around!
Your turn. Tell us about your off grid building plans, or your favorite design guides below.
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