POLE BARN QUESTIONS

HAPPYNC · Mar 5, 2019

I'm looking to build a open sided 40x60 pole barn. There will be a metal truss lean-to on one side and eventually two or three shipping containers on the other side of the barn with a lean-to shed over them also.

I'm using metal trusses pre-engineered for 140 mph winds. I'm in central NC and the highest winds I've ever seen was during Hugo in 1989 with sustained winds of 55 mph and gusts of 85 mph.

My plan is to use 20' 8x8 PT post, 10ft on center. I don't think I need it but I would probably do 2x10 banding around the top of the post with angle bracing on each post. The metal trusses have their own horizontal truss ties.

I would like a minimum of 13 ft sidewall height, preferably 15 ft.

My questions are, is the 8x8 enough for either 13 or 15 ft height and how deep and wide should the hole be? The frost line is only 12 inches. I figured on using concrete and cross drilling 2 or 3 holes in the post with rebar alternating north/south and east/west.

EddieWalker · Mar 5, 2019

Are these treated 8x8's? I've never seen them before, only 6x6 treated posts, which would be more then strong enough for your application, or just about any other application. The only 8x8 posts that I've ever seen or installed where cedar, and they cost 5 times as much as treated 6x6's

RNeumann · Mar 5, 2019

This guy has good info.

RR Buildings
- YouTube

Designing and engineering your structure when you need a roof rated at 140mph is a bit short sided. I’d spend a few bucks having an engineer answer those questions and back it up with their stamp .

3Ts · Mar 5, 2019

With just the roof and no sidewalls, it will wiggle, but should be ok. There are slenderness ratios (cross section vs. height) that you'll need to watch for and can find them on the web. It will wiggle no matter the size of columns until they are cross braced which essentially means a wall. I question the 10' spacing because there will be times you'll want to be wider to get stuff in and out.

M5farms · Mar 5, 2019

Yes 8x8 will be sufficient . I have them on my 50x60 , when I built my 32x60 in November I used 6x6 but came off each side with 15' leans and used 6x6 on them . I put my holes at 48" used a 12" auger for 3' dug the rest of the way down by hand with hole diggers

HAPPYNC · Mar 5, 2019

3Ts said:
With just the roof and no sidewalls, it will wiggle, but should be ok. There are slenderness ratios (cross section vs. height) that you'll need to watch for and can find them on the web. It will wiggle no matter the size of columns until they are cross braced which essentially means a wall. I question the 10' spacing because there will be times you'll want to be wider to get stuff in and out.

Well, to be perfectly honest, I have everything bought but the post and concrete. I bought 2x6x12 for the purlins. The business I bought the metal trusses from is just a reseller/retailer. Afterwards, I found out the trusses are from a company in Alabama just above Pensacola, FL which explains the higher wind rating.

When I checked out their website and then called and spoke to someone, I read and was told 10 ft max. It WAS originally gonna be a 40x72. I'd rather be safe than sorry and maybe just add another truss later on if I still need it. The bad thing is I'll have to chop 2 ft off every purlin. Argh!

HAPPYNC · Mar 5, 2019

EddieWalker said:
Are these treated 8x8's? I've never seen them before, only 6x6 treated posts, which would be more then strong enough for your application, or just about any other application. The only 8x8 posts that I've ever seen or installed where cedar, and they cost 5 times as much as treated 6x6's

Lowe's in this area source their lumber from a local supplier. You can go to the Pro Desk and special order bigger and longer than what the stores stock. They are pricey but I can get a discount on them that helps a little. They are pressure treated pine.

HAPPYNC · Mar 5, 2019

RNeumann said:
This guy has good info.

RR Buildings
- YouTube

Designing and engineering your structure when you need a roof rated at 140mph is a bit short sided. I’d spend a few bucks having an engineer answer those questions and back it up with their stamp .

I've seen his vids. He does quality work. I don't need a 140 wind rating. That's just what they came as. The company I bought the trusses from buys them from a coastal AL truss fabricator which explains the high wind rating.

What's funny is I called the permit office....always a cringe worthy action. They want engineered footers and post design even though the trusses came with engineered drawings. The permit was around $330. A local engineer wanted $3000 to draw it up. Said it was 40-50 hours work at $75/hour. That's a great price..........if you're an engineer. Not so much for me.

The flip side of that is the permit office said if I was a farm, I needed nothing more than a Farm# from the local FSA (Farm Service Agency) and my cost would be no more than a zoning permit just to make sure I was zoned Ag. Cost....$10.50. Luckily, I have a farm number being some of my land is leased.

Guess which route I'm leaning towards?

KennyG · Mar 5, 2019

You are more than good with your approach. Around here, I don't think I've ever seen 8x8s used. My pole barn 40 feet wide and uses 4x6 posts on 8 foot centers. If you only have 13 foot sidewalls, I think 16 foot long poles would be fine with your limited frost depth. I have 12 foot sidewalls with 16 foot poles but our frost depth is over 3 feet.

HAPPYNC · Mar 5, 2019

M5farms said:
Yes 8x8 will be sufficient . I have them on my 50x60 , when I built my 32x60 in November I used 6x6 but came off each side with 15' leans and used 6x6 on them . I put my holes at 48" used a 12" auger for 3' dug the rest of the way down by hand with hole diggers

That's good to hear. I have a 12 inch auger bit but thought about renting an 18 or 24 inch and digging 48 inches deep. I was looking to do the same on the lean-to with the 6x6 posts. It's a 24 ft lien-to.

Is yours in Florida? If so what type of soil do you have? Mine is red clay but I have a good bit of "potato rocks".

M5farms · Mar 5, 2019

HAPPYNC said:
That's good to hear. I have a 12 inch auger bit but thought about renting an 18 or 24 inch and digging 48 inches deep. I was looking to do the same on the lean-to with the 6x6 posts. It's a 24 ft lien-to.

Is yours in Florida? If so what type of soil do you have? Mine is red clay but I have a good bit of "potato rocks".

sandy loam , Im in panhandle . Its easy to open the hole up with a pair of hole diggers after you bore the 12" hole

HAPPYNC · Mar 5, 2019

I feel safer with the 8x8 on the barn and 6x6 on the lean-to. I'm starting to think disturbing less soil and using a 18" hole would be better for me. An 8x8 (7.5x7.5) is around 10.5 corner to corner so that would give me almost 4 inches of concrete around the corners.

cycle_gator · Mar 6, 2019

I am building a 30x50x15.5 corner posts are 6x6, sides are 6x8. Posts are on 10’ centers, purlins are 2x8’s. Plans were engineered for open sides with 50 psf snow load and 80 mph wind load. Posts are set 4’ deep on top of 6” of concrete in 2 ft diameter holes. Posts also have uplift plates installed.

Zebrafive · Mar 7, 2019

I would look into laminated posts. Below ground portion treated, rest untreated.

zzvyb6 · Mar 7, 2019

I have 8x8 treated posts on the front of my 30 x 50 3 sided 'shed'. I added 4 sliding doors that needed some support by the posts because they started to warp. I strapped some highway U channel on the sides to keep them straight. The only weight on them is from the headers and the T-111 framed doors.

HAPPYNC · Mar 7, 2019

cycle_gator said:
I am building a 30x50x15.5 corner posts are 6x6, sides are 6x8. Posts are on 10’ centers, purlins are 2x8’s. Plans were engineered for open sides with 50 psf snow load and 80 mph wind load. Posts are set 4’ deep on top of 6” of concrete in 2 ft diameter holes. Posts also have uplift plates installed.

These are engineered with 20 psf snow load which is within spec for my area. Even though they're treated posts, I planned to give the buried portion an oil bath before sinking them.

Zebrafive said:
I would look into laminated posts. Below ground portion treated, rest untreated.

I've ordered the 8x8x20s. $152 each, 10% discount, and then I had another 6% off card so total per post was $137.27 with tax. Expensive and probably overkill but once and done. I wouldn't even know where to get a laminated post around here.

zzvyb6 said:
I have 8x8 treated posts on the front of my 30 x 50 3 sided 'shed'. I added 4 sliding doors that needed some support by the posts because they started to warp. I strapped some highway U channel on the sides to keep them straight. The only weight on them is from the headers and the T-111 framed doors.

What is highway U channel?

Barnbuilder · Mar 10, 2019

With a 8x8 you better be dead on with a 18" hole. Post that large is a PITA to move if its off. I would go 4' deep especially if you have 15' walls. Out east it might be pretty easy with very little rock. I usually bore 24" even with 6x6. I would think for an AG building you wouldn't need a permit. In Union county if you call it a "barn" you don't need one. Head of Inspections Dept told me that, I couldn't believe it.

HAPPYNC · Mar 24, 2019

I'm from the Unionville area. Live in Stanly County now. Not everyone of course but in general, dealing with inspections over here is a nightmare. I'm covered under Ag though but I felt better with the overkill considering my wall height. I can rent an 18" or 24" bit for about $35/day and a 1 ft extension for $10 if I need it. I considered drilling deeper, pouring a footer then setting the posts on that. I can cut the tops off to level up as needed.

The problem with going to a 24 inch hole is it actually doubles the amount of concrete and of course cost. Neither is really enough for a concrete truck and that's an awful lot of 80 lb bags. As for moving it, I planned to put a sling around one end to be able to move it with the tractor forks until I can them braced.

Barnbuilder · Mar 25, 2019

The weight of the concrete helps with the uplift especially if it's an open shed. You might bore a hole and stick the post in to see how much wiggle room you have before you get started.