slab in pole barn. what to do with poles?

[kevinO]

New member here. I want to build a workshop and am leaning towards pole barn construction.

I have spent lots of time pouring over many of the messages on this board about pole barn construction and have learned a lot. But I'm still not sure what to do with the poles in a pole barn when a slab is poured.

I have read that it is best to not pour the concrete directly against the poles as the concrete will trap water and cause the poles to rot. Suggestions were to put a concrete cookie in the bottom of the hole or possibly pour a concrete "necklace" around the post and then fill with gravel, dirt, etc - but not concrete!

But what do you do with the poles when you pour the slab in the barn?

I asked a buddy of mine that has poured concrete for twenty years. He said to just concrete the whole thing up from bottom to top. I said "what about water getting in and rotting the poles?".

He said "you are going to put a roof, walls, etc on the barn aren't you?". I replied "yes". He asked how then were the poles going to get wet?

I couldn't answer!

He said that the "don't pour concrete around posts" logic apples to decks, fence posts, etc which are exposed to the elements, but enclosed posts are a different story. He said that the slab adds a lot of side to side strength to the building when poured against the poles.

So I'm confused. I like this guy a lot (and he volunteered to help with my slab for free!), but his argument seems to be contrary to what I've read here.

One thing I thought of as a compromise: I figure that with all the water coming off the eaves when it rains, the ground on the side walls can get very wet. Perhaps this water can make its way into any cracks in the concrete around the posts. Maybe a compromise would be a concrete necklace at the bottom, then fill with gravel, dirt, etc and then four of five inches of concrete at the top (the slab). This would allow the bulk of the pole to drain, and the top part should not get wet unless some soaks in from the bottom, but I'd assume that it would also then dry out when conditions change.

I don't want to goof this up! My wife already thinks that I don't know what I'm doing!!!

Thanks for any tips!

Kevin

 

[JimR]

You could always use telephone poles for the poles. I never saw one of these rot at ground level or below.

 

[MicroPilot]

How about pouring footers for the poles up to the level that the floor will be poured? Or pour the floor first then set the building on that.

 

[phantom309]

Excellent question Kevin, and welcome to the list!

I've wondered the same thing as I'm starting to kick the tires on a new workshop and am considering using pole barn construction.

I do not recommend that you put the poles on top of the slab. All of the tie-downs that I have seen will hold a pole to the slab, but they will not do a good job of preventing the pole tiping over. One of the big benefits of a pole building is that the poles resist forces from wind. You lose this benefit if you put the poles on top of the slab. If you do that, you might be better off just going with conventional stick frame construction...

Mark

 

[EastTexFrank]

I think I agree with your buddy ... fill the post hole with concrete and be done with it. It always seemed to me that backfilling around a post with gravel, sand or dirt, which will be very porous and permeable in the case of gravel, more so than the surrounding earth, will allow the water to gather and pool around the post and that's the very thing you are trying to avoid. Cement, on the other hand, is basically impermeable when set and won't allow the water to contact the post in the first place.

I don't know if this will help but I'll throw it out there for discussion.

Fill bottom of hole with concrete. Set cardboard tube (from box store or builder's supply) in concrete to 2" above sub base. Set pressure treated posts inside tube and fill space with concrete. Bend rebar to 90 degrees and set in cement in top of tube facing in towards slab. Backfill around tube with dirt and tamp. Set out rest of rebar for slab. Pour 4" concrete slab.

That would allow the post to be totally surrounded with concrete and tied back into the slab. Framing the slab might be a bit of a pain with having to notch around the tubes or you could just frame to the outside of the tubes. Assuming that the level of your slab is slightly higher than the surrounding ground, there should be no way for water to get trapped around the the posts.

Sounds a bit like overkill but I think it'll work and should be good for your lifetime.

 

[beenthere]

</font><font color="blue" class="small">( Maybe a compromise would be a concrete necklace at the bottom, then fill with gravel, dirt, etc and then four of five inches of concrete at the top (the slab). This would allow the bulk of the pole to drain, and the top part should not get wet unless some soaks in from the bottom, but I'd assume that it would also then dry out when conditions change.
)</font>

You are on the right track. Only thing I would do is put a 'sleeve' around the pole (post) of 1/2" strip (used to separate concrete poured against a building that allows a pad to move) to allow the floor to move independent of the wood post.

Gravel packed and tamped around a post sitting on a concrete pad will stay pretty dry under a covered building, and I would want to allow some movement of the posts independent of the concrete floor (that gets into the mechanics and wind loads applied).

Wood needs to remain dry, although the treated wood you most likely are using will last a long time if 'under roof'. I wouldn't (nor would anyone understanding wood) set a post in concrete. Sometimes it is easier, and quicker, and it feels real solid after its done, but it doesn't last (and is a bear to remove when it rots off).

Good luck with the doubtful wife. /forums/images/graemlins/wink.gif

 

[CTyler]

</font><font color="blue" class="small">( But what do you do with the poles when you pour the slab in the barn? )</font>

When I put the plastic down over my base I covered the poles as well. Then poured the floor.

As far as your friends comment on how thier going to get wet?
Pretty simple really, only part of the pole is inside. The rest is in the dirt on the outside edge of the building. If you don't have your slope right from the building they will go from getting wet to getting soaked.

 

[Dave___in___CT]

Hi...


As suggested... I'd keep a gap between the poles and concrete slab allowing them to move independantly... and also help prevent that being a moisture trap...

Regarding moisture... concrete is not waterproof... even if there is no direct contact with water from outside... the poles and concrete are exposed to moisture in the soil... moisture in the air...

Water penetraits even 8" thick concrete basement walls... they can sweat from the moisture in the air...

Also as suggested... treated utility poles typically have a long in-ground service life...


Dave...

 

[SPIKER]

one of the bigger things to cisider is when pouring crete over and or around poles is the wind shear load, the poles while in-ground can move some sideways and not have much shear load as the load disapates as the post sways back and forth a bit. when it is poured up/around it it creats a spot where a good gust can cause the poles to SNAP OFF at the level of the concrete. also the moisture will codnese inside on the poles near or at ground level often and wall poles will get wet form ground moisture. water is fine on the poles and will not damage them it is the leaching of the concrete that is more damaging! it is acidic or alkalie (forget which) but that is what mixes with the water and causes the rott more so than just water, which does little to offend the TREATED wood...

watch how many telli poles are preplaced from rott vs ones on or in sidewalks from same rott and or damage form wind?

I do know that pouring on the pole is a no-no... as for FIX?
best bet is to use styrofoam to insulate the slab from the poles this let water vapor and such to stay away from the pole... this would be a guess on my part, only so maybe others know better way?

I will be having to deal with this same inssue soon, as I have center poles in my 40' wide pole barn, that need to be addressed. I've let it set comming up on 2 years and have back tamnped with spud bar on all the poles. (after first tamping it has settled nearly 10" next to the poles, using clay, sand & gravel as back fill on the poles, (stuf that came out of the holes with gravel mix.) it's my understanding that the friction of the material around the pole will keep it from slipping out and the wiggeling back & forth helps keep the post settled all the way ON the pad at the bottom of the hole. (below frost heave required!) dust/dirt will keep entering into the wiggled spots untill it can't wiggel anymore and friction keeps it there wqith above barn weight.

anyhow I'm reading with passion too for my OWN peace of mind!

Mark M /forums/images/graemlins/smile.gif

 

[neilly2]

I'm not familiar with pole barn specifics, but one thing that is basic to construction---wood never contacts concrete unless the wood is treated. Take a look at the first floor sill plate on any home built in the last 20 years. (that's what is between the basement wall and the floor joists.

I don't know what type of wood you're using for the posts. But if you're going to set it on the concrete make sure you treat the bottom with tar or some equivalent. Even if its cedar or pressure treated.

Personally, I would use a Simpson strong tie base plate that gives an inch between the wood and the concrete. Someone mentioned that the interior columns experience a rotational moment force. This sounds odd, but again, I'm not that familiar with pole barns. In conventional framing the wind forces or racking of the house is resisted by the sheathing or diagonal bracing of the outside walls.

The structural affect of the slab around the poles is nothing and should not be considered.

I would welcome the help but not the advice. I have always offered to help people for free when its something I've never done before. That is because I want to learn on their house first, before I tried it on mine.