Pole Barn Question

I am having a 30' x 40' x 10' pole building built this spring by a contractor-----will have county building permit. The sides will be metal as will as the roof.

OSB is HEAVY! My three machine sheds without OSB have trusses at 9 or 10 foot intervals. Those trusses are made of large 2x, no 2x4 tops or bottoms. More like 2x8 or 2x10 and are made of the best quality lumber. Really beautiful lumber. The 2x4 purlins are on edge in all of them.

Why the OSB?

Gerald J.

Steve, You might want to ask your contractor how many inches, center to center, that he is figuring for the 2x4 purlins.  With the additional weight of the OSB plus sheet metal over the 4' span, you may want to decrease the distance from say 24" down to 18"?  Or, you could put 2x6 purlins every 24"?  You may also want 1x4 flat fur strips on top of the OSB to nail or screw the sheet metal.  These 1x4 spaced at 2'or 3' would allow the sheet metal to flex some & offer an additional air gap for insulation purposes plus it wouldn't add much expense. 

Steve-Ohio wrote: I am having a 30' x 40' x 10' pole building built this spring by a contractor-----will have county building permit. The sides will be metal as will as the roof.   The roof will be 5 pitch with trusses 4' on centers and 2' x 4' perlins with 7/16' OSB and metal roof on top of OSB.   Question for you folks--what do think about trusses being 4' on center with  it carrying the weight of OSB and metal sheeting ? It will be approved by county engineers.   Tks Steve

I worked for a truss company for 2 years.  just make sure they know the loading and spacing

You can save $$$$ by using the 2" insulation blanket instead of OSB.  My 40 x 84 barn is built on 12' centers with 2x8 gerts set between double trusses with joist hangers. Snow load is 40#...standard design for our county.

But the underlying framing and trusses are more expensive.

My 40 x 70 x 14' shop has trusses every 12'(4/12 pitch),built in 1963,'old school',still straight,level and plumb! Roof has 3 x 4 purlins every 2',sports a metal roof.That leaked so the previous owner layed down 1/2" plywood and 2 layers of shingles.

It seems to me that you should be asking the questions of you contractor.  He is the one who should be aware of your local requirements as to loading and building codes, and also is the one to stand behind it.  If you do not have confidence in your contractor, then perhaps he is not the best choice to build it.  There are numerous methods of building a post frame building, and some are better for specific uses than others.  Compare methods with your contractor, and let him give you the best advice for your situation.

OSB is heavy, id go the styrofoam sheets for a vapor barrier, may cost a little more, but will work better, and a lot lighter. you need to keep the roof itself as light as possible, there shouldnt be an issue with the purlins faiing, It is usually always the trusses that fail from snow load or weight.

Eldon:  Making a statements  like "You can save $$$$$ by using a 2" insulation blanket" and "underlaying framing and trusses are more expensive" indicates you are knowledgeable enough to make an argument, but have not checked the facts.  OSB is less per sq. foot than 2" insulation.  The extra load carring capacity of the truss/purlin structure needed to carry the OSB  would be so small ,that it would not even be a factor.  7/16 OSB = 1 lb./sq ft. This is 1/40 of the engineered load carring capacity  of the roof structure.  To use "underlaying framing and trusses are more expensive" as a consideration not to use some kind of sheathing OSB, plywood or wafer board would be a statement to be made for the sake of argument, but not based on engineering facts.

I built my pole barn myself. used 2x8 rafters with 2x4 purlins 24"O.C., then steel. When weather and temp are right, it's like raining inside. But that's not a problem.

When I built my 28 x 40 shop, I put 1/2" CDX plywood over the rafters, building paper (tar paper), 2x4 purlins and steel roofing. I didn't want it to "rain" on the loft. And it doesn't. Steel roofs result in condensation so the vapor barrier is important if you don't want moisture. Leave the OSB off if you don't use a vapor barrier but plan on some dripping.

Bob@allisdowneast     

If you use osb you need a water barrier between the metal roof and osb.  It will be damaged otherwise. I would consider some 1/2" fanfold Styrofoam.  Installation cost will be lower for it in saved labor and material cost should be lower when you take the OSB + vapor barrier cost into account.

My barn is surrounded by oak trees.....gets pretty noisy in there when the acorns start falling!

Bob, ya could be right, though I didn't see any of the wee buggers last fall when the nuts came down! I do know that the roof got mighty slippery - I think due to pollen and dust - not sure even the squirrels could stay on it.