Pole Barn Design Questions

[bwharper78]

I am working on plans for a small pole barn to serve as a workshop and equipment shed. The barn will start completely open and I will enclose it as I get the time and money. I want to build a 12' x 24' center barn with a 9' shed on one side. Sills at 10' high with a 12/12 (or other steep angle) roof and loft. My plan was to build it old fashioned with lumber cut from my property. I am afraid I will never be able to do what I want and still comply with code. I called the building department and they said that it would need to be permitted, but they could not tell me specifics on the codes, just that they use International Building Codes.

- Where can I find codes to reference? I have found a lot of codes online for other jurisdiction, but where can I find the base international codes?
- Will it be possible to use my own lumber and rough sawn and still pass inspections?
- I want to build my own rafters, but everything I read seems to say engineered trusses are required, is that true?
- I read a lot of people putting posts on 10' and 12' centers, but codes seems to specify 8'??? I am in the south with no snow.

Thanks

 

[s219]

You would need to have an engineer "bless" your custom milled lumber. So it may be more convenient and less expensive to use graded lumber from the store.

That only applies to the structural timbers of course, so you can still mill your own siding and trim. Plan to let it season a year per inch of thickness before using it.

Your county or state website should have links to their uniform statewide building code (or similar terminology). It is probably based in international code with some tweaks. Normally you can download a PDF.

I see no reason you can't use rafters with a pole building, but rafter ties would probably be good to keep the walls from bowing, as well as collar ties. At that point, trusses may be simpler. If using rafters, you would need to decide if a ridge beam is required, and make sure a pole is able to support it on each end if that were the case. Can probably get by with only a ridge board.

If using trusses, they will probably need to have signed/certified drawings to pass code. Truss companies normally provide this at no charge.

My pole barn has posts on 10' centers on the back gable wall, which is 20' wide (the opposite front gable end has a 10x10 door so spacing is set by that). But the posts are on 8' centers on the eave walls. I am sure that spacing comes about when you consider the loads coming down from the roof to the poles, as the header on the eave walls is supporting the entire roof load.

If you go to a truss company website, they can tell you what snow load is required for certified trusses in your area. Even in parts of the south there will be a snow load requirement, though it might be small. Here in my part of VA, I plan for 10psf structural load and 20psf snow load when designing roofs.

Knowing the square footage and loading of the roof, you can then figure out the load on eave header beams and size those. Then work out the post spacing and sizing needed to support the headers and walls. Finally, work down to the footer sizing for your soil type, as required to support the poles.

By the way, it might make sense to plan to close the barn in from the very beginning. You'd probably need to make different material choices for an open pole barn, and that could get more expensive than needed for something that is eventually closed in.

Good luck!

 

[quicksandfarmer]

A lot of the answers are going to depend on the state and the county. In Rhode Island you can use rough sawn lumber for agricultural buildings, anything else requires stamped graded lumber. But you have to be recognized by the state as a farm and your land has to be agriculturally zoned.

Trusses aren't required. But the whole idea of a pole barn is to be simple and cheap. And then more cheap. Trusses, purlins and metal roofing allow you to construct a roof with a lot less material than a standard residential roof with rafters, sheathing and shingles. Metal roof doesn't require sheathing. Using purlins instead of sheathing you can space the rafters or trusses further apart. Trusses are stronger than rafters so you can space them further. Further spacing means less materials.

If I'm reading your post right your barn is only 12' wide, which means each rafter only spans 6'. I don't have a rafter span table handy but that hardly seems worth a truss.

You don't often see trusses in steep pitches because they have to be brought in on a truck, which limits how tall they can be.

 

[s219]

Been looking at rafter tables lately, and you can get away with 2x4 or 2x6 rafters over a 6' span depending on other factors.

 

[farmer2009]

Not to high jack the op's thread but I am Getting ready to build a Gabriel roof on a pole barn/ storage building. Haven't had much luck finding information on construction of one as pitches are what ever so it seams but my question really is.
How to determine rafter and beam size It will be 16 feet wide. Thanks.

 

[KennyG]

My first thought is to go 12 foot instead of 10 foot on the walls. I know that sounds high for 12 foot wide building, but if your 9 foot wide wings have only a 1 in 4 roof slope, you will still be under 8 feet on the outside walls with 10 foot main walls. To maximize flexibility in how you close it in, I would not have any walls less than 8 feet high.

My other thought (and I'm sure you saw this one coming) is that it's too small. A 12 foot wide building is wasting a lot of support capability on the poles. If it was me, I would look at 16 to 20 feet wide with a 6/12 main roof (play with the rafter tables and see what length and spacing will be economic). If you have room, I would then leave room for 12 foot wide lean-to's on each side with 3/12 or 4/12 roofs. Years down the road, you will be glad you have the options.

 

[Xfaxman]

Not to high jack the op's thread but I am Getting ready to build a Gabriel roof on a pole barn/ storage building. Haven't had much luck finding information on construction of one as pitches are what ever so it seams but my question really is.
How to determine rafter and beam size It will be 16 feet wide. Thanks.

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