Poles in ground vs on concrete posts

[toyotadriver]

I've got a 30x40 stick framed shop building on a slab foundation. I need some additional covered storage so plan to add onto the shop building. I don't plan to install walls....just want to extend one of the gable ends of the building and extend the same roof line.

So, the extension will be the same as pole frame construction minus the siding. It will be attached to the existing shop building. I'm debating on pouring concrete pillars or sinking the posts into the ground. I like the idea of putting the posts on top of concrete pillars because then rot of the posts becomes much less probable. But, I wonder if the posts mounted on top of the concrete pillars will create problems with the building potentially swaying.

Also, if you recommend sinking the posts in the ground, would you use concrete to fill in around the posts or gravel or soil?

I'll be using 6x6 treated posts.

Any thoughts?

Here's a link of something very similar to what I want to do.

http://www.tractorbynet.com/forums/projects/233771-adding-pole-barn-extension-existing.html

 

[matt_i]

Best and longest lasting would be something like the perma-column setup. The buried wood is fast and cheap and might buy 20-30years or more.

The lack of moment support (post on top of concrete column with simple uplift sheetmetal-strapping) could potentially be overcome by heavy "X" bracing the structure but that ends up looking kooky and limits the function as you have to walk and drive around it.

 

[readhead]

The continued roof diaphragm should overcome most of the moment. Using sonotubes with some kind of anchor brackets should do the job.

 

[toyotadriver]

The continued roof diaphragm should overcome most of the moment. Using sonotubes with some kind of anchor brackets should do the job.

My plan if I put the posts on top of concrete would be to use something like this to anchor the post to the concrete:

http://www.fastenersplus.com/Simpso...-Zmax-Finish?gclid=CJWKrOvKi9ICFQe5wAodNEUKrQ

 

[mrobins297aaa]

when I did my barn the inspector said he didn't want to see anything touching those post but dirt, no concrete because he said the water would get between the post and the concrete and rot the wood.
so when we poured the floor and rat wall he required between them I fastened roof shingles to the sides of the posts to keep the concrete off them

 

[kbs2244]

Glad to know your inspector knows his stuff.

I have posted this before, but it is the best pole barn construction book I have found.


http://www.pole-barn.info/pole-building-construction.html

 

[73RR]

You can easily set a sono-tube in the ground and fill it with concrete. If you go 18" or larger then you could eliminate rebar.
Make a bracket like the design here: http://www.nfba.org/uploads/Rigid_Connections-Jan_2017_FBN.pdf

 

[toyotadriver]

Thanks for all the input. Any other thoughts/recommendations?

 

[Falcon67]

I want a covered extension over the driveway of our shop. Thought about posts and concrete and such. One thing in my mind is concrete pads with a length of 4 1/2" square steel tube to receive 4" posts.

 

[tinysparky]

both work. Drainage away from your building will be key in either method.

You will want to have a concrete in the bottom if you use gavel. Depending on the size...will determine the concrete pad. For my lean-to, it was just engineered to have a 18" by 6" pad in the bottom of the hole with compacted rock back-fill. the main structure gets a 24" x6" concrete slug in the bottom.

 

[toyotadriver]

both work. Drainage away from your building will be key in either method.

You will want to have a concrete in the bottom if you use gavel. Depending on the size...will determine the concrete pad. For my lean-to, it was just engineered to have a 18" by 6" pad in the bottom of the hole with compacted rock back-fill. the main structure gets a 24" x6" concrete slug in the bottom.

Drainage won't be a problem. The whole house and shop were both designed with drainage in mind.

I think I'm leaning toward digging the holes, putting some gravel in the bottom, dropping the post in, setting the bottom of the post with some concrete, and then filling the remainder space around the post with well packed clean base gravel.

Thoughts on that plan?

 

[readhead]

Post on concrete pier= no rot. Post in the ground= starts to rot the day you install it. Doesn't seem like a tough decision to me.

Now come all the replies that say "my building has been up for twenty years with no problems". How do you know? When was the last time you dug around the post to inspect it?

 

[tinysparky]

I can't believe you would recommend that readhead (just joking). This is one of those questions where $$ factors in heavily. would i love to use steel posts mounted to concrete columns....sure.....

However there are a some great ways....perma style....steel, etc....lots of good.....concrete, gravel with drainage....and some that some people disagree with....using dirt or clay to re compact....if they even choose to re-compact. In 4 months I am using concrete pad, gravel back-fill, then a concrete lid with 2' overhang and gutters.

It will work for me....but for you, no warranity will be provided

 

[readhead]

I didn't say anything about steel posts. You are digging a hole any way. The minor expense of a sonotube, concrete(mix yourself) and a post anchor seems superior to me.

 

[toyotadriver]

I didn't say anything about steel posts. You are digging a hole any way. The minor expense of a sonotube, concrete(mix yourself) and a post anchor seems superior to me.

I like that method but my concern is that the point where the post connects to the concrete seems like the weak point to the whole thing. I'm not worried about the posts lifting off but am slightly worried about the posts swaying. I don't want cross bracing if I can help it so this addition needs to be able to not away on its own. It will be connected to the existing shop building but I am still concerned with it swaying. Seems like poles in the ground would help transfer the strength of the wood to the structure.

 

[AMCguy]

I like that method but my concern is that the point where the post connects to the concrete seems like the weak point to the whole thing. I'm not worried about the posts lifting off but am slightly worried about the posts swaying. I don't want cross bracing if I can help it so this addition needs to be able to not away on its own. It will be connected to the existing shop building but I am still concerned with it swaying. Seems like poles in the ground would help transfer the strength of the wood to the structure.

I would be more concerned with how the post connects with the overhead structure.

If it was mine, I'd dig out and pour a footing with a curb wall. You could have your posts as far off the ground as you want. That way you could contain gravel in the addition or pour a concrete floor. If you ever decided to close it in, you'd have something to build on.

In my opinion, if the main shop is built on concrete, then so should the addition.

 

[readhead]

The roof diaphragm will keep the posts from swaying.

 

[buddyboy]

the concrete pad in the bottom of the hole is to keep your pole from sinking.

you want zero air around the post that is in the ground

concrete around the post is not a good idea...wood shrinks and so does concrete. this will leave a small gap all around the post just big enough for air

air+moisture+wood=rot

any pole that rots it is always at the surface where moisture and air can work together

the reason you use poles is cost savings, if you're not putting them in the ground you should go stick built

if you have good drainage and pack the fill in tight around the posts you'll have a structure that will last as long as any other method of building

 

[kj_mustang]

Wood rot requires air and water. Buried posts only rot at the ground line. Keep water away from your posts and they will not rot.

 

[buddyboy]

yes, keep away either moisture or air... easier to keep away air, try to keep away both and you'll be fine

 

[toyotadriver]

This addition is covered only. It's only for parking a camper and possibly a boat as well as some farm implements under cover. There won't be any walls or doors. I plan to put down gravel to park on. I don't need concrete there at this point. Basically, I'm wanting to build something similar to the post I linked but it will match the roof line on the existing shop and will not have sides. It will be about 26 wide by 30 ft deep.

 

[ryan77]

"the reason you use poles is cost savings, if you're not putting them in the ground you should go stick built"


I agree!

 

[toyotadriver]

"the reason you use poles is cost savings, if you're not putting them in the ground you should go stick built"


I agree!

When you refer to stick built for an open structure only (no side walls) how would you do it?

I understand what stick built means for building on a slab (that's how my current shop is built). The issue is, this isn't an addition to the existing shop in the traditional sense. It's an open addition with posts and a roof structure connected to the existing shop building. No side walls.

 

[readhead]

They didn't read #21

 

[buddyboy]

oh, didn't know it was going to be in the open.

you could consider it like a deck, except you are replacing the deck with a roof.

burying the posts would be the cheapest, easiest. and possibly the cleanest look (depending on who is looking at it)

putting in concrete piers would cost more and the brackets to attach the wood (or steel) poles could be pricy. and the concrete columns would need to be above grade 4 to 6 inches to avoid moisture (or why even bother?)

i'd just put poles in the ground... worst case is one or more rots away in 25 or 30 years and you'd just brace up the roof, cut the pole out, and replace it. in 30 years treated poles shouldn't be more than $100 a piece

 

[kbs2244]

Find some guys that put up power poles.
(Maybe even hire them.)
You will find the drill the hole, put about 6 inches of gravel in the bottom for drainage, put in and plumb the pole with about 18 inches of gravel around the bottom.
They the keep checking for plumb as the tamp the hell out of the gravel, add 12 inches of dirt and tamp it hard into the previous layer of gravel.
Then more gravel, tamp, more dirt, tamp, until full.
The idea is to ram the gravel/dirt mix so hard that it pushs into the undisturbed dirt around the hole.

They put the first drainage gravel in because the tops of their poles are exposed and rain water will wick down to the bottom and soak the pole if not allowed to drain out.
If you put a roof over your pole tops you could skip it.
But since you need it as you fill and tamp you might as well do it right.

The key is the hard tamping, never any concrete.

Concrete makes it too hard for the water to drain down.
If you want to make a 3 inch thick collar around the pole at ground level to keep the grass away, that is ok since it will also keep the water away.

 

[kd3pc]

you may want to look at this recent post:

http://www.garagejournal.com/forum/showthread.php?t=353084

It shows a "pavillion" apparently well built on behalf of our federal government that suffered failures on the poles to concrete post attachment....

well worth a look!

 

[tdkkart]

If wooden posts in the ground were as sure to rot off as some people think, here in Iowa we'd have pole buildings rolling across the countryside every time the wind blew.
We have literally thousands and thousands of pole buildings with the poles directly in the dirt with no gravel or concrete around them.
I grew up in Iowa farm country, I've seen a LOT of rotten wood sitting on top of concrete slabs, foundations, and pilings, I've never seen a failed pole building due to rotten posts in the ground.

 

[lakeroadster]

Find some guys that put up power poles.
(Maybe even hire them.)
You will find the drill the hole, put about 6 inches of gravel in the bottom for drainage, put in and plumb the pole with about 18 inches of gravel around the bottom. .......

The difference here is if the telephone pole sinks a few inches... who cares. if your building support columns sink, that's a big problem.

OP.. you need, as others have stated, to place a concrete puck, 4" thick x 18" diameter, down in the bottom of the hole for the column to sit on. Then just pack the space around the column with the same dirt you took out of the hole.

Also... where are you located? Pressure treated columns will last 50 years, even in humid conditions. Much longer in arid climates.

 

[Franz1.0©]

The difference here is if the telephone pole sinks a few inches... who cares.

The American Bald Eagle on final approach.
Do you have any idea how much beak he's going to take from Mrs Eagle & the kids if he misses the arresting wire?

 

[ptgarcia]

For your carport I'd pour a simple concrete footing with post anchor keeping the bottom of the post an inch or so off finish grade. There won't be any sway issues if you have enough of those 6"x6" posts. What you're talking about is basically the same thing as a patio cover. Check with you local governing agency and they'll tell you how large the footing needs to be, but 18" sq x 12" deep is likely enough.

 

[ssdave]

The pole building concept is that you don't need to have lateral bracing against sway, because the post base anchored in the ground is ridgid against rotation (moment resisting). A pole building with buried poles resists sidesway by it's pole structure, and requires no other lateral bracing. That's why it's the cheapest type of construction.

Putting in a concrete column and then putting the post on the column with some kind of a base and anchor negates the moment resisting design of the pole building concept. So, you have to design alternative bracing against sway. In an open carport type of structure, it doesn't have the walls acting like shear panels to resist swaying. As mentioned before, the roof will somewhat tie it to the existing building, but to me, that's a pretty weak structural element to resist lateral wind forces. I think you'd need substantial diagonal cross bracing between the posts to make it acceptable.

I'd build it with buried poles, per true pole building design, and know it will work. Posts on concrete columns will not be very stable.

 

[toyotadriver]

The pole building concept is that you don't need to have lateral bracing against sway, because the post base anchored in the ground is ridgid against rotation (moment resisting). A pole building with buried poles resists sidesway by it's pole structure, and requires no other lateral bracing. That's why it's the cheapest type of construction.

Putting in a concrete column and then putting the post on the column with some kind of a base and anchor negates the moment resisting design of the pole building concept. So, you have to design alternative bracing against sway. In an open carport type of structure, it doesn't have the walls acting like shear panels to resist swaying. As mentioned before, the roof will somewhat tie it to the existing building, but to me, that's a pretty weak structural element to resist lateral wind forces. I think you'd need substantial diagonal cross bracing between the posts to make it acceptable.

I'd build it with buried poles, per true pole building design, and know it will work. Posts on concrete columns will not be very stable.

Thanks. That was my concern as well.

 

[toyotadriver]

you may want to look at this recent post:

http://www.garagejournal.com/forum/showthread.php?t=353084

It shows a "pavillion" apparently well built on behalf of our federal government that suffered failures on the poles to concrete post attachment....

well worth a look!

Thanks for the link! That's exactly what I was concerned about. I do have an existing building to attach it to but I'm still concerned that there could be twisting from side to side if I don't put the poles in the ground. Looks like putting the poles in the ground is what I need to be doing. Thanks for the link.

 

[dbabicky]

Also if you pour concrete down in the hole around the pole, wrap the pole with tarpaper or ice and water shield where the concrete and pole contact each other so that the concrete and pole can slide independently if you are in a frost area. It'll help prevent a wavy roof in the winter and spring. LOL !!!
I'm with the camp of burying the pole. It's up to you if you want to use dirt, gravel, gravel and dirt, concrete, or concrete and all of the above in the hole with the pole. I am agreeing with TDKKART on this one. I live in Wisconsin farm country and there are pole barns built this way that are in excellent shape and I personally know they have been standing for 40+ years.

 

[mrobins297aaa]

here's the post they used on my barn

 

[readhead]

I'm always amused by the folks that say that the building is in perfect condition. They have absolutely no idea what the condition of the poles are. The only thing anyone knows is the day it collapsed. Nobody digs around a pole to inspect it. Of course there are buildings that have been standing for years but the quality of wood was better years ago compared to today. On the other hand I have demolished the remnants of a twenty year old haybarn with rotten PT poles and replaced it with a metal building.

This is the ford vs chevy of construction and will of course never be resolved. If you weren't sure I'm not a fan of burying wood in the ground but I respect the decision of others to do what they feel is best for them even if I can't convince them otherwise.

 

[ssdave]

I'm always amused by the folks that say that the building is in perfect condition. They have absolutely no idea what the condition of the poles are. The only thing anyone knows is the day it collapsed. Nobody digs around a pole to inspect it. Of course there are buildings that have been standing for years but the quality of wood was better years ago compared to today. On the other hand I have demolished the remnants of a twenty year old haybarn with rotten PT poles and replaced it with a metal building.

This is the ford vs chevy of construction and will of course never be resolved. If you weren't sure I'm not a fan of burying wood in the ground but I respect the decision of others to do what they feel is best for them even if I can't convince them otherwise.

In this case, it's not a ford vs chevy type of decision. The constraints of an open carport construction make a post on top of concrete footing structurally unstable. It cannot be safely be done, without modifying the structure to not be open/free standing. Anchoring to the end of the existing building is not adequate bracing against lateral movement.

In general, I personally agree with you; I wouldn't invest in a building that relies on buried wood posts for it's structural integrity. I always build for myself, frame buildings on conventional footings or on floating slabs, but they are structurally braced panel walls, not pole buildings. But, when I have to design open carport type buildings, I use braced frame construction. Pole buildings if I have to because of cost, or steel moment resisting frames with appropriate massive concrete footings if longevity and reliability is more important than cost.

 

[readhead]

Ssdave, I don't disagree with your comments and I believe this can all be distilled down to money. Pole buildings are fast and inexpensive compared to other types of construction. It is however not permanent. It satisfies an immediate need and functions quite well.

My comment about ford vs chevy alluded to the fact that there will always be two camps that are unlikely to agree any time soon.

 

[red61cj5]

I used perma columns to negate the rot problem, and sheathed the outer walls with plywood (under vinyl siding) to make it laterally stable. I think itll be here long after I'm gone.