DEAR POLE BARN GURU: I have a question regarding truss loads, specifically ceiling loads, for a pole barn. I know you have touched on this before, but I was hoping for a little more detail.
I recently purchased a property that came with an existing pole barn, and other than a few material ratings I cannot find any data on the trusses (no manufacturer tags, etc). The building is 32×48, and the trusses 4/12 pitch with 2×6 top cord, and 2×4 bottom cord and webbing, on 4′ centers. I want to add a steel ceiling, plus insulation and lighting. By my math I am looking at a dead load of 2-3 lb/sq ft, including the weight of the bottom cord of the trusses.
I have done a lot of research on the subject, and it seems that it is common in pole buildings to have trusses spaced much wider than 4′ (8’+ seems common). Is the tighter spacing a indication that these trusses should support a 2-3 lb/sq ft dead load for ceiling and insulation? If you were specing trusses for my requirements, how would you design them? If these trusses are not sufficient, what sort of reinforcement would be required?
One of the only bits of data I have been able to find is this page https://www.pole-barn.info/gable-roof-trusses.html, where toward the bottom it lists a 30′ span with the same lumber sizes as my trusses. While it says “no ceiling” it also lists a bottom cord dead load of 5 lb/sq ft, which would be plenty for what I have planned. BAFFLED IN BOZEMAN
DEAR BAFFLED: The spacing of the roof trusses has no influence upon their load carrying capacity. In reality, trusses spaced 12 feet on center could easily have a greater ceiling load carrying capacity than ones placed even every two feet!
As a starting point, you should assume the trusses are NOT designed to support dead load weight of anything other than the trusses themselves, required bracing and minimal wiring and lighting.
The size and or grade of the truss chords as well as the webs and their quantity, and the size of the roof truss plates may not be adequate to carry the weight of the ceiling load. It’s not as easy as just knowing the size or spacing of each part, but rather it’s more of how all the parts function together in any configuration. In other words, it’s a formula with many parts which change the final answer of “yes” or “no”.
The only safe way to make sure your new ceiling doesn’t end up on the floor with the rest of the roof following it, would be to hire an engineer to confirm the trusses are adequate to support the ceiling load, and to design a repair for them, if necessary.
DEAR POLE BARN GURU: We are builders, putting up a Hansen Pole Building currently. It is large enough so the main clearspan building and attached shed had to be shown on two different pages of the blueprints. Anyhow, we made a mistake on setting the poles. Where we are looking at the 4 posts going across up by the “matchline” we have the left sidewall posts set correctly but the 2 main building posts and the right side shed post are set incorrectly. We ran a string line but the workers ended up setting those 3 posts on the other side of the string line.
I am wondering if there is an easier solution than pulling out the posts. We have a lot of concrete in the holes and it would be hard to get them out. Could we fir out the left sidewall posts and go out and buy longer purlins? ERRANT
DEAR ERRANT: While this doesn’t happen often, you are not the only person to have this problem. In this particular case, you are constructing an engineer certified post frame building, which means any deviation from the plans is going to have to be approved by the engineer. This is going to mean time delays and the expense of paying the engineer.
Even if it was not an engineered building, using purlins for a span which is now 5-1/2 inches greater could overstress the purlins in bending. While 5-1/2 inches may not sound like much, in the design calculations for the purlins, the span is squared.
I’ve had to pull out concreted in columns before, and it isn’t fun. Best method I found was to use a backhoe or loader, wrap a chain around the column and lift it out. Fairly fresh concrete can be chipped away from the column and the process of setting the three columns can begin again.
I’m sorry I don’t have an easier solution, but you will be much happier with the outcome if you do reset the posts. And all in all, it may end up being far less expensive as well, in both time and materials. As I said, I’ve done this myself, so I am right there with you. The good news is, once you reset the posts, just knowing you have things all “in order” will make the project run smoothly from here on out