pole building on slope "foundation" question

[Marctrees]

Hi all - Planning a 30x40 typical "pole barn" shop using like 6x6 posts. I think 8'OC, Rob-Bilt or similar.

I totally understand how it's all done, on a level surface.

In our case though, the grade drops about 30" over the 40' run.

So,we will , apparently, have the grade built up so the concrete floor elevation is like 8" above natural grade on the uphiill side, no problem, but now it ends up 38" above grade at the other end.

Ok, so the simple thing to do is just make an oversize pad, and slope away from building to natural grade.

BUT- due to closeness to an existing building and other reasons, we cant have that pad extension, rather we need to drop down plumb.

So that side of the building ends up with top of slab about 38" above grade.

How is that "kneewall" or whatever it's called handled?

On a metal frame building foundation, I know what would be done, but Pole Building floor is totally different.

I know all about how the lowest girt is treated and ends up being the concrete form on a level install, and how the concrete is usually poured after building is mostly built, but what is the order of events in our case, and what do we end up with?

O. and I don't mind if that kneewall is treated wood on its showing face, if it's cheaper than concrete.

And I assume the grading contractor would really prefer to make the pad BEFORE the posts are up. so he can drive around compacting his lifts without anything in the way.

Thank you. Lars

 

[Marctrees]

Kinda like this photo, but less severe slope. Lars

 

[188slo50]

Is your garage door side the low side?

 

[Marctrees]

No, it's basically on the high side.

The whole situation is similar to the photo, but less drop overall, and an even slope.

I'm starting to think ---- Forget , for a moment, it's for a pole barn.

Rather, imagine I want a level parking pad.

So, we build a retained wall pad just a few feet bigger than building size.

We have a local option for virtually free "used" power company poles.

Verticals sunk in about 3' in bored holes, cocrete backfill,maybe 8' OC. then long poles stacked on inside.

The highest the wall will be is like 3'.

Now have the pad built, filled and compacted.

Now, pad is totally done.

Then just have like Robbilt come in , and build their usual way WITHIN the confines of this pad.

Like a foot in, so they are not worried about hitting the wood retaining wall with auger or whatever.

So, their bid should be the same, or very close, to if it was level originally all around.

The only complications I see for the builder, Is they can only auger when on the pad, not outside, and they need to go 3' higher on their ladders.

I think both issues not important.

I just seems to me this may be the simplest and cheapest.

Your guys thoughts?/ Thanks, Lars

 

[olytdi]

You may get away with it depending on the integrity of the poles, how deep they are set, how long you want it to be robustly stout, etc.

Wood moves and gives. That may not be a factor for you but if you want a poured floor in the shop itself, the foundation on which it resides MUST be stout and not moving over time. That means one of two things: either put riprap down with a large enough apron such that nothing will move over time (the way I did mine on a slope) or pour a balloon footing that integrates a wall and floor over the fill that has been amply compacted.

The posts may look adequate initially and may be actually if the apron is far enough from the building perimeter. But, if it is too close, the fill against the poles will "squirt out" from under the building over time as the posts move/deteriorate.

Hope that helps!

 

[Marctrees]

I think, the above "deterioration" won't be for like 30 years or so, with creosoted posts and horizontal poles.

The "Used" poles failed from storms mostly. Trees falling on/ near them etc.

I will be long gone after a portion of that 30 yrs.

Lets say, I MAY want it to last longer as an "upgrade".

Bang for the buck. other options?? Lars

 

[Marctrees]

Set 3' deep, projecting up 3 ' max.

No deadmen. Lars

 

[bmxdad]

Front of mine is level, back side is 18" above grade. I went out an extra 2' per side, and will be adding a block retaining wall on the sides that are above grade. This is to keep the compacted crushed rock from slowly spreading out.

Could you add a wall and fill it in prior to digging post holes and pouring the slab?

 

[Marctrees]

BMX - "Could you add a wall and fill it in prior to digging post holes and pouring the slab? "

Well ya, that's what I'm thinking in my subsequent post or two above, but still looking for more thoughts, supporting that idea, or something different .

Thank you, Lars

 

[Daniel Dudley]

In your case I would do a foundation. For me it would be easier. But if you can get some of those big concrete blocks that they use for retaining walls, you could put them outside your wall and infill to them.

 

[sickjuice]

Only proper way is a concrete grade beam foundation imo. And I would do a post-tension or structural floor because you will never compact 3' of fill well enough for the floor not to crack

 

[volleyball]

Can you bring in fill to level the area and then slope that away? What about taking from the high side several inches/foot or so to bring it down?
Does the entire floor need to be one level? You could have a lower floor area giving you more headroom on that side.

 

[bjcouche]

I really hate it when people simply refer me to a "professional" but that's what I would suggest you do in this case. I would recommend you contact an architect, structural engineer, or the like. I had my "pole" building built cut into a steep hill, so steep the back wall of the building is 8' below grade. This required a lot of concrete. I had a well known "pole" building mfg take care of everything and they subcontracted an engineer, and that whole subcontracting process didn't go so well... Search the forums some more, there are several horror stories of people adding several feet of fill and then pouring a floor only to have disastrous results. Either the floor cracks and heaves badly, or in one case the concrete block wall holding IN the fill, like in your case blew out. The back of the building sagged and the concrete floor broke.

I'm no expert here, but if I had to add that much fill, I'd be sure I had somebody who knew what they were doing both engineer it and someone skilled to do it.

The cheapest option I can think of is to lower the high end, and put up a retaining wall several feet from the building. Then your building itself would be typical pole building construction. It's possible though that lowering it isn't possible based on your garage door placement.