20' X 24' Pole barn on 25% slope - best method?

[DwayneB2021]

Hello to the forum - thanks in advance for any input. I read a number of other threads on the forums here about how to approach placing a pole barn on sloping ground, but not sure any of them really addressed my particular situation. Essentially the entry to the barn is at grade level (20' wide) and the ground slopes away at 25% along the 24' depth. Which means the "rear" corners of this floor would be 6' high.

See the attached images showing side views, they show two different approaches to build this barn:

1) Local contractor claims they can dig a ditch around the perimeter, then build up a retaining wall with very large rip-rap "boulders", then fill the interior with compacted gravel, then pour a slab, then build a pole structure above the slab. This has advantages of being able to park a car or truck in the barn if needed, although mostly this will be used to store a BX1500 tractor and other equipment. Disadvantage is having a huge pile of ugly rip-rap under this building (will be visible from the road). And not certain that this rip-rap "boulder" retaining wall will truly remain stable for the long haul.

2) Amish barn builder suggested a post building supporting a reinforced wood platform. This would use 6" by 6" posts, (about 22 total) with a post row under the center of the floor. The floor would be tongue-in-groove covered by plywood. Advantage is that this is much cleaner appearance on the outside (no giant walls of rip-rap). Disadvantage is that while it would easily hold a tractor and implements, might not be adequate to support a car or truck. Not a "forever" building, but would surely last as long as I am kicking.

The Amish guys are a little pricier. But I have seen their work on other barns in the area and it is excellent.

Any thoughts about either of these approaches or alternative approaches?

Appreciate any ideas you might have.

 

[Rustyiron]

It would add $$$ to the building, but footers and a 4' poured concrete wall (actually foundation) would be the most attractive or at least look like normal house or garage construction.
Then there's simply getting some fill dirt to level this "pad" and the gradually sloping away so it could be mowed.
I'd take a guess that the concrete option might be $3-4000 and somewhat make this building look taller, at least from the back. Also your builder will need to switch from post holes and use the steel brackets to attach the posts to the concrete. That may add a few bucks for the building but it might be a "wash" as it means no hole digging and might eliminate the need for pt lumber.
I don't like putting wood in the ground anymore, I just don't trust the new treatment and one day it will rot and fail.

 

[Egon]

Side hill?

Dig into the side hill wider and deeper than than the pole barn. Dig & fill method. Get a nice gentle back slope to the excavation. If suitable use the excavated material to pad out in front of the excavation. Finally make a drainage ditch around the side and back of the excavation. Then use ordinary building procedures With cement floor.

Six foot depth may/will end up as less using cut & fill method.

 

[DwayneB2021]

It would add $$$ to the building, but footers and a 4' poured concrete wall (actually foundation) would be the most attractive or at least look like normal house or garage construction.
Then there's simply getting some fill dirt to level this "pad" and the gradually sloping away so it could be mowed.
I'd take a guess that the concrete option might be $3-4000 and somewhat make this building look taller, at least from the back. Also your builder will need to switch from post holes and use the steel brackets to attach the posts to the concrete. That may add a few bucks for the building but it might be a "wash" as it means no hole digging and might eliminate the need for pt lumber.
I don't like putting wood in the ground anymore, I just don't trust the new treatment and one day it will rot and fail.

Going to do this one time so the $$$ are not really an issue.

It's a good suggestion, had thought of this but I wasn't sure about the post construction on top of a standard foundation with footers. I had read somewhere about "wet anchors" for posts to be placed in the concrete slab, but you'd have know with total certainty where you wanted them.

Share the same concern about any wood in the ground. Probably OK for 5 years or so but beyond that, as you say eventually it will degrade.

Problem with any of these contractors it is hard to find someone who will do the whole job. Some do concrete only, some do pole structures only, and so on. Getting a little too long in the tooth to tackle a project like this myself.

 

[sandman2234]

I was just wondering where that 36" side entry door was opening out to? Seems to be that first step might be an issue. I agree with Rustyiron, putting wood in the dirt nowadays isn't as good of an idea as it used to be. In Florida it is even a worse idea, since you didn't include your location. I do know your not in Florida, because we don't have many of this types of issues, and rocks of that size to back fill the building.
David from jax

 

[DwayneB2021]

Side hill?

Dig into the side hill wider and deeper than than the pole barn. Dig & fill method. Get a nice gentle back slope to the excavation. If suitable use the excavated material to pad out in front of the excavation. Finally make a drainage ditch around the side and back of the excavation. Then use ordinary building procedures With cement floor.

Six foot depth may/will end up as less using cut & fill method.

Thanks for the suggestion. I've heard about this method, and I guess you could excavate into the hill,and use some of that material to "pad up" the rearward downslope area. Seems like the main advantage of that method is reducing the amount of fill - although the concrete pad still needs to be at grade on the left in these sketches, so wouldn't volume of fill be the same? Seems like you would still need a retaining wall of some sort around this earthen pad which will be supporting the concrete floor (and the weight of equipment). This is a clay area when you get down a foot or so. That stuff is pretty greasy, over time gravity will try to slide the concrete pad/gravel/earth fill on down the slope unless you have some retaining wall, especially on the downhill side.

 

[DwayneB2021]

I was just wondering where that 36" side entry door was opening out to? Seems to be that first step might be an issue. I agree with Rustyiron, putting wood in the dirt nowadays isn't as good of an idea as it used to be. In Florida it is even a worse idea, since you didn't include your location. I do know your not in Florida, because we don't have many of this types of issues, and rocks of that size to back fill the building.
David from jax

David - yes you are right we will need to build up some steps to reach the side door. Main entry would be the 16' garage door to the left in these sketches, which will be ~on grade. I am in Ohio, so subject to frost/freeze. Have to get down 36" or more with any sort of footer. Wood in dirt even if treated is not ideal, agreed. I've been thinking about this project for a while now, unfortunately it's the only spot for a building on my property.

 

[s219]

6’ high on the downhill end is near my comfort limit for a pole barn base where you put in posts at grade (footers below frost line) but not out of the question. I’ll go take a pic of one I did that was about 3’.

Basically you build the pole barn normally but need longer posts on the downhill portion. At some point after it’s framed, you bring in self compacting gravel (#57 or #78 is my preference) and backfill and level the floor. The gravel spills out under your skirt board at a normal angle and forms a sloped berm around the barn. Once done, cover the gravel with a compactable material on the outside to finish the berm to the desired grade.

Instead of a sloped berm you can instead (or in combination) build a retaining wall on the downhill end.

 

[DGZRT]

Building a Garage into the side of a Hill

Hey, Would love to get lessons learned on building into a hill. I spent the weekend looking at some older posts but did not cover all my concerns. Because of my property layout the best place is to build into a hill on the other side of my driveway across from the house. I am planning on a...

www.garagejournal.com

This link might give you some ideas . or some links for your research

 

[DwayneB2021]

6’ high on the downhill end is near my comfort limit for a pole barn base where you put in posts at grade (footers below frost line) but not out of the question. I’ll go take a pic of one I did that was about 3’.

Basically you build the pole barn normally but need longer posts on the downhill portion. At some point after it’s framed, you bring in self compacting gravel (#57 or #78 is my preference) and backfill and level the floor. The gravel spills out under your skirt board at a normal angle and forms a sloped berm around the barn. Once done, cover the gravel with a compactable material on the outside to finish the berm to the desired grade.

Instead of a sloped berm you can instead (or in combination) build a retaining wall on the downhill end.

When you say your comfort level, what's your concern about the 6' downslope height? Is it the pole length? These have to go 4' in the ground, so it would be a really long pole for sure. 10' just to get up to floor level, then another 15' or so above that. Can they even get a 6X6 25' post?

I hadn't heard this approach to filling inside the post array and allowing the gravel to naturally slope outward. Are you thinking about a concrete slab on top of that #57/#78 gravel?

One builder was proposing lining the post array with tongue-in-groove and filling gravel inside that box. I really didn't like that idea, because once that wood degrades/rot, the wall would burst outward. I guess if you made the box walls with 2X12 treated planks with moisture barrier that would be pretty substantial. But not a "forever" solution.

Thanks for this idea it's a new one I had not heard about.

 

[DwayneB2021]

Building a Garage into the side of a Hill

Hey, Would love to get lessons learned on building into a hill. I spent the weekend looking at some older posts but did not cover all my concerns. Because of my property layout the best place is to build into a hill on the other side of my driveway across from the house. I am planning on a...

www.garagejournal.com

This link might give you some ideas . or some links for your research

Thanks DGZRT, didn't see this thread I have searched out similar all over the Internet. I will check it out. Seems like everyone has a slightly different purpose or situation so it's hard to find an exact match. Really envious of my neighbors who have nice flat lots and plenty of area to construct their buildings. It's hard to get any contractors interested in this project, they all want the easy ones.

 

[LouNY]

If I'm looking at your diagrams correctly, I don't like either of your proposals.
Is the property line just 8 feet from the rear of the structure?
If so I'd definitely not go with the so called retaining wall of large stone.
Also the wooden wall would not be repairable in several years with that narrow of a working area.
My only way would be spread footers with the tops of the footers below frost level,
they can be stair stepped from the back wall to the front. Then pour a stem wall for a
post frame building to be set on. The long expanse on the back wall would likely need a couple of
reinforcing columns to be used. Then the interior can be filled with compacted gravel and a slab poured.

 

[ultrarunner]

I have 22x30 on down slope giving lots of storage under the top floor with full 7' height going back 20 of the 30 at ground level grade.

My upstairs floor is concrete over plywood supported by joists...

Glad to have the extra room for my BX23, air compressor, shovels, etc ..

 

[DwayneB2021]

If I'm looking at your diagrams correctly, I don't like either of your proposals.
Is the property line just 8 feet from the rear of the structure?
If so I'd definitely not go with the so called retaining wall of large stone.
Also the wooden wall would not be repairable in several years with that narrow of a working area.
My only way would be spread footers with the tops of the footers below frost level,
they can be stair stepped from the back wall to the front. Then pour a stem wall for a
post frame building to be set on. The long expanse on the back wall would likely need a couple of
reinforcing columns to be used. Then the interior can be filled with compacted gravel and a slab poured.

Lou, that's one reason why I don't like the boulder retaining wall proposal, proximity to the property line. I might be able to situate it to give a little more margin. But even if I did that it does not get around the fact that this would be one huge pile of ugly rip-rap which will look more like an industrial coffer dam than anything else. So I am thinking I will cross that one off the list.

Not sure what you mean about a wooden wall. Proposal #2 is a reinforced wood platform supported by posts/joists. No fill, it's a wedge shaped void under the floor. Essentially like a raised deck platform. Are you talking about needing to get under this structure to repair joists for some reason? Not quite able to visualize your suggestion, might need a sketch.

Ultimately as someone else mentioned, the best solution is a poured concrete foundation with proper footers - the end result would be very similar to the poured walls of a walkout basement. So that will be my next call, to get an estimate for that, I am sure it will be costly but once built, that will be here 50 years from now. Not sure about either of the other proposals.

 

[DwayneB2021]

I have 22x30 on down slope giving lots of storage under the top floor with full 7' height going back 20 of the 30 at ground level grade.

My upstairs floor is concrete over plywood supported by joists...

Glad to have the extra room for my BX23, air compressor, shovels, etc ..

Gotcha - the underside of this building won't be useful for us, even if I had storage space under there. This is because there is a 25% grade leading down to a "lower floor". Maybe I could build some sort of access road to get down there... but it would not be trivial.

One thing you said was interesting - concrete over plywood? I have never heard of that. Could you explain that?

 

[s219]

Here are a couple photos from additions I have added onto my pole barn over the years. This older addition had about a 3' drop to the rear, which I handled with an extra skirt board (marine lumber, will outlast me) and a crude log retaining wall:

At the time I made a mental plan to come back and make a nicer retaining wall or just dump gravel there and slope it, but that was about 5 years ago and the clock is still ticking on my plans. Surprisingly, the logs are still solid too, but that won't last forever. I'd probably use marine lumber for the permanant retaining wall (they make a tongue and groove material for bulkheads that is real nice). But the prices will need to drop/stabilize before I spend that kind of money.

Here's another addition where I used an extra skirt (ground contact 2x10) and then let #57 gravel spill out from under the skirt boards until I had a nice sloped berm. The berm was topped with crusher run and then wood chips, and has held up well. That was probably about a 4' drop at the low corner (closest to the camera).

I put a dead-main in the middle of the rear skirt extension (you can see the bolts and plates), just in case any pressure was put there by the gravel. So far the skirt has not budged after a few years of parking cars in there, so either it wasn't a problem or the dead-man is doing it's job. If you have sufficient posts that can handle the retaining load, then a dead-main isn't needed. For instance, on the eave walls I have a lot of posts to support the header and roof load, and did not put dead mans there.

I think if this was planned properly with large long posts, you could incorporate a retaining wall (full or partial) into the main poles of the barn. They'd have to be long enough to frame the wall and go down below your frost line to a footing, so that could be the issue -- those might be very long posts when all that is taken into account ($$$ and or availability issues).

That assumes you are wed to the pole barn method. I happen to like it myself for many reasons. But it works best and is the most econimically viable when you can build on flat or mildly sloped ground and if you are OK with a gravel floor. Once you pour a concrete floor in a pole barn, you may have been better off building with standard stick-framing on a slab, or stick framing on a concrete block foundation.

BTW, you can do a concrete block foundation that will handle a 6' drop and then backfill that with gravel. It just needs to be engineered properly. Don't know the cost or feasibility of that myself. I just know that the garage on our main house has a block wall and sloped about 4' front to back. The back of the foundation has 4' of gravel and concrete debris to fill it out and support the slab.

 

[ultrarunner]

It’s common in the SF Bay Area…

Concrete Slab supported by wood framing…

I too have a steep grade as it drops 8’ in 30’ but Kubota and 2wd pickup no problem on well compacted gravel

I did not original permitted construction… as always I said should have been 24x30 or even 24x 32 or 36…

Wood floors not allowed in garages so concrete needed…

 

[s219]

Found pictures of our garage foundation, first is before gravel fill, notice that far corner:

Now here it is after gravel:

Looks to be about 6 courses of block below the gravel in the far corner, so figure about 48" of fill there. All built to code and kosher.

Hope that helps!

 

[Diggin It]

Rock. Lots of rock. Build up to a level grade then build the barn as normal. If the fill can be tapered off sufficiently, you'll be able to mow and all the road will see is a grass hill with a barn on top.

Check with contractors or the area road departments to see if they need a place to dump spoils from projects.

 

[Egon]

Thanks for the suggestion. I've heard about this method, and I guess you could excavate into the hill,and use some of that material to "pad up" the rearward downslope area. Seems like the main advantage of that method is reducing the amount of fill - although the concrete pad still needs to be at grade on the left in these sketches, so wouldn't volume of fill be the same? Seems like you would still need a retaining wall of some sort around this earthen pad which will be supporting the concrete floor (and the weight of equipment). This is a clay area when you get down a foot or so. That stuff is pretty greasy, over time gravity will try to slide the concrete pad/gravel/earth fill on down the slope unless you have some retaining wall, especially on the downhill side.

You dig into the hill more than the building depth. Same goes for the sides. The building site can so arranged to not sit on fill.