Pole Barn - Why not use center post?

[gabeancounter]

Hi folks,

This is my first post. I have read for days and days about pole barns. Great info! Still have a few questions that "google" has not been able to help me with.

Looking to build a pole barn and trying to understand why everybody is using clear span- trusses?

The size I would like to build is 30x50. 5- 10' wide bays.

1. Why not use the center post method like in the picture below and eliminate all the roof trusses and extra lumber cost? Seems it would eliminate the need for a crane or FEL as I don't have either.

2. Is there any down sides to this design?

3. Right now home depot has 2x8 Yp lumber is cheaper than 2x6. Using 2x8x10 for the purlins seem like over kill? 2x10 for the rafters (?) (outside post to center post) ???

4. Thinking I will use 2x8 hangers for the purlins off the rafters - any downsides?

5. Wanting to make my post 3 or 4 2x6PT laminated. I understand the ground contact version is what should be used - but I am thinking if I coat the post with "fence asphalt paint" that it will add enough protection? The TSC has some called "black beauty".

FYI These pics are from polebarn101 website. They are not mine and I am not connected to them - just the only pics I could find like this.

Also I am in east GA and the barn will be used for keeping a pickup, tractor, implements, two trailers, lawm mower etc. No livestock etc. Thanks

 

[blueriver]

Center post are fine ... if you don't mind working around them. Clear span simply opens the entire building up, you won't ever run into a post or back into one with trusses

 

[civesnedfield]

Second what blueriver says. Another thing is if the building is being used for loose housing for animals, they tend to like to rub against the columns.

Trusses tend to be a cheaper way to go. If you don't want a center column.

 

[gabeancounter]

Yep. I know its another post to avoid but I figure if I miss the outside post then I should not hit the center post.

Any suggestions on this framing method?

 

[blueriver]

Your talking about 10' bays ... are you planning the rafters 10 O.C. ? Use a double plate and you could go with 2x8 rafters 5' O.C. and use 2x4 purlins

 

[SandburRanch]

Two reasons for trusses. 1) As BR says, freedom of movement with equipment. 2) Plane Jane rafters will sag over time, even 2x12s that length.

If truss rafters are built correct they will have camber added at the time of manufacture and become more straight as roof load is applied.

This building pictured has 3 laminated 2x6s for post with the center 2x6 shortened to accept the truss bottom chord. The outer laminate on the end posts were left short to accept the rafter bottom chord. By placing the rafters in the post the need for a top plate band or double band is eliminated which saves a bunch of material. The trusses were ordered with the purlin clips attached. Construction is a breeze.

I believe a real serious pencil would be needed to come out ahead by not using truss rafters. Just my opinion though.

 

[LD1]

I can think of a few more reasons to add to what has already been mentioned.

Typically, trusses are a little faster to build with. And if you dont plan on going with extreemly tall walls, a typical 30' W truss can be set without special equipment. A few friends and a days work.

If you buy trusses from a mfg, they will all be the same. Ensuring a straight ridgeline and square roof. As opposed to trying to get all of your cuts and measurments exactally the same with rafters.

Trusses are also easier if you plan on finishing the interior. They give you a flat bottom cord to attach interior pannels for a flat interior ceiling. And thus a place to insulate if needed.

And back to them being easier and faster to build with..... Once the truss is set on top of the walls upsidedown, one person on each wall and one with a 2x4 to push the peak up into place. The two people on the walls secure the truss into place. Once this is done, you can simply walk out on the bottom cord and start securing the purlings.
BUT...with rafters, you have to set the ridge beam first. And then try to set the rafters in place, one at a time. With no way to walk out on them until they are already secure. All the while trying to keep things symmetrical and square on both sides.

 

[SandburRanch]

Yep. I know its another post to avoid but I figure if I miss the outside post then I should not hit the center post.

Any suggestions on this framing method?

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This will help you lay out the first pattern rafter when you get to that point. It's called the step off method.
Laying out a common rafter - Fine Homebuilding Article

 

[gabeancounter]

Thanks for the replies so far.

Blueriver,
That is correct- rafters every 10' with purlins between. If I go 5' then I need an additional post?

Sanburranch,
That is a fine looking barn. I really like the design. Pretty much what I am trying to build. Purlins placed the same way. How much for trusses designed like those?

 

[alchemysa]

Over here in Australia most barns (garages) are all metal construction and use prefabricated metal roof trusses. (Usually 'C' channel). Often, only the end trusses are fully braced. The centre trusses are just inverted 'V's. (It works here but it wouldnt carry a ton of snow).

Anyway, I imagine a prefabbed truss (wood or metal) is going to be a lot easier and quicker to build with. Everything will be square and equal and should give you a neater result. You might save a few bucks in timber but might spend a lot more time trying to square things up. And I'm sure you'll curse centre poles eventually.