Pole Barn Truss Sizing and Spacing.?

Question

I was pricing pole barn packages at Menards, and they claim to meet my local 30lb snow load with 30' trusses rated 39lb on 8' centers with 2x4 purlins standing on edge on 2' centers. Is this a good idea? Would the boards under the trusses be much smaller than normal because every truss is nailed to a post?
I'm wondering about buying residential trusses, rated 62lb on 2' centers, would those pass my 30lb code if I put them on 4' centers?

Why would 8' truss spacing be too expensive if they can get away with supplying 2x4 purlins? The basic materials price for 30x56x12 with colored steel, no doors, no windows, no overhangs, 4' of post underground, is $6591, which didn't seem too bad to me. I'll have to put up purlins to attach my ceiling to the bottom of the trusses, but that's the only excess cost I can think of, unless the specified trusses are a lot more expensive than residential trusses. I'm kind of worried that I'll end up with valleys between the trusses. A 2x4 on 24" centers doesn't seem like much to span 8' with.

Another, slightly related question: I want to insulate the slab and make a "rat wall". I'm thinking of nailing 2'x8'x3/4" ply on the outside of the posts below grade (would I get away with .40 since it isn't structural?) and putting 2" foamboard on the inside face of the plywood, then pouring my concrete up against the foam. Anybody have a better plan?

PS: The price quoted did not include any interior, Just the structure, precast 4"x14" footings, and edge trim pieces. I'll be putting up OSB on the inside of the walls and on the ceiling later when I need to insulate it.

Talked to my local code department. As suspected, 14x4" footings are very undersized. Minimum in Eaton County MI for a 30' wide is 18x8". I hadn't intended to use precast footings anyway, but now I know my 12" auger isn't enough.

Answer 1

8' o/c trusses are not aproblem in post frame buildings with a metal roof. 2x4 2' o/c on edge are typical for a 30 lbs. snow load. As one post said, it is just harder to screw the roof steel on being that you only have 1.5 inches to hit rather then the 3.5 inches. In terms of the headers, or truss carriers as some poeple call them, yes they will be smaller if based upon a 8' o/c truss if all of the trusses are set to hit the posts. Make sure you take into account doors that may change your post spacings.

I would, however question the footing size. Places like Menards or Home Depot are notorious for undersizing footings. I would recommend at least 6" thick, preferably 8" thick. At 4" thick, the main concern is the post "punching" through the concrete. You do not get full advantage of the 14" diameter if you are only using 4" thick.

Answer 2

Pole Barn Trusses

Answer 3

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Answer 4

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RE:
Pole Barn Truss Sizing and Spacing.?
I was pricing pole barn packages at Menards, and they claim to meet my local 30lb snow load with 30' trusses rated 39lb on 8' centers with 2x4 purlins standing on edge on 2' centers. Is this a good idea? Would the boards under the trusses be much smaller than normal because every truss...

Answer 5

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Answer 6

I'm building a 40x64 pole barn.

Trusses on 8' are cheaper, but hard to build because the 2x4 on edge are hard to hit with screw pattern.

Trusses on 4' are a little more expensive but the 2x4 purlins lay flat on top of the truss which gives you a wider spot to hit. Way easier to build. I use 2/ 2x12's on top the post just like a header with a 2x6 as a nailing plate for the trusses, this way you don't have to be exact with your posts, due your lay out and start setting trusses.

Answer 7

Best thing to do is get the engineering specs and submit that with your building permit application. If the app is denied, they'll tell you why. Eight foot centers isn't too wide (but it's getting close), since the 2x4s running lengthwise up the slope are on two foot centers. The trusses act like beams, only tilted. The 2x4s support the load and the trusses support the 2x4s. I'm assuming it's a metal roof. Personally, I would be more comfortable with four foot centers. If these are wooden trusses, they should be the same as house trusses.

The fact that they fall over a post doesn't affect the truss at all.

Answer 8

The spacing will be dependent upon several factors including: - design loads (live and dead loads) - truss type (howe, W) - wood species (southern pine, doug fir/larch, SPF) - roof pitch I can tell you that depending on your design loads, there are definitely trusses available with a 2x6 bottom chord that span 34ft or more on 24" centers. So, it's not inconceivable that you can go with 24" centers, but you need to confirm your design loads and find out from the truss manufacturer if the trusses you have meet those loads on 16" or 24" centers.

Answer 9

Menards Pole Barn Kits

Answer 10

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The spacing for roof trusses is generally 16'' oc. But you can order trusses for 24''oc (somewhat more expensive). You need to speak to the specialist at your lumber yard , they will be able to help you. The lumber dimension of the elemnets of the trusses is not the determining factoring in their strength, the engineering is. Keep in mind 24oc" requires thicker roof sheathing, so you have to do the math on costing the roof system