Backfilling pole barn, need advice

[DrewStyduhar]

Hi guys,

Just finished a 40x48 pole barn. There is ~12" gap below the bottom of the skirt (2x8) that I need to do something with. This was intentional as the barn is on a slight grade and I wanted to raise it up a bit due to the crazy rain we get here in NC. Due to complications with the county, the building pad was built up just enough to create a level area for the builders to do their thing. Even then, this resulted in ~2.5' of fill in the back. Yes, I understand it would have made more sense to build pad up to

I have ~14" that needs filled up INSIDE the barn. I figure 4" concrete + 4" #57 and ~8" of compacted sandrock would do the trick. The outside we will blend off using cheap fill dirt. Should I double skirt this building with a 2x10 below the existing 2x8?

Just curious if anyone has been down this road before...the builder said they typically put the skirt right on grade but that wasn't going to work in this situation.

thanks for any advice!!

Drew

 

[KennyG]

I wouldn't add skirting. In addition to the fill inside, I would fill outside to gently slope away with rock, at least a couple of feet. In addition, maybe lay landscape cloth under the outside fill. Then you should be in good shape for water resistance.

 

[deezler]

I take a different opinion than Kenny and certainly would add more skirting now, especially with how easy it would be to do here. Shoot, I laboriously dug down 24+" around my pole barn perimeter on the inside just to pour a concrete rat wall. Keep the critters from undermining your slab! Plus erosion benefits, etc. It will also make your backfilling easier, allowing you to keep the inside fill separated from the outside fill, etc.

 

[DrewStyduhar]

Thanks for the info

Ya know....rock is damn expensive right now or else I would go wild and fill the building up with it. The local quarry gives away free dirt from processing and we have a ton of dirt work to do on the outside so thats why I was thinking about using that for the OUTSIDE. Sandrock is ~200 bucks a load right now.

Deezler - I priced ground rated 2x10x16's and they are ~$55 each so double skirting would prob cost me in the neighborhood of ~$600 or so. I tried to get tongue and groove before building was up but it was special order and we ran out of time. I think the fill inside and outside will keep that second skirt from going anywhere. According to the plans the finished EXTERIOR grade should be the BOTTOM of the skirt shown in the pic.

Thanks!!

Drew

 

[nybirdman]

Similar situation two years on my pole barn build;skirted the outside with PT lumber and back filled the inside with crushed stone;then tamped.

 

[jaxs]

Additional skirt board doen't prevent flooding inside. Besides that,I haven't found decent ground contact material for several years.

 

[Randy Gann]

I live in McLeansville just east of Greensboro. Have used crushed concrete from Martin Materials. Can get fines that works like sand rock or 57 size. Price is much lower than real stone. I live in an older home with skirting across the back of the house. I had vinyl mobile home skirting for years but recently replaced with pvc trim boards. The pvc was not cheap but is durable and paintable.

 

[Midniteoyl]

If you have groundhogs and moles *now* would the time to dig ~14"-18" below the planned floor grade and fill with gravel, about 12"-14" wide. Since you are already above grade and need to build up you are ahead of the game. Add the shirt board, add #57 gravel against it extending out ~14" as you build up around it. Already getting gravel for inside, so pretty cheap and keeps the digging critters out.

 

[s219]

No problem doing it this way. I have built several pole barns on a slope and did leveling at the end. I usually have to add extra skirt boards on the low end. I like to fill the inside with #78 or #57 gravel which self compacts. Let it spill under the skirt to the outside as you rake it into place on the inside. You can backfill against the outside of the skirt with something more substantial, either fill dirt of crusher run (whatever is cheaper or more available).

The absolute answer to the question is to let slope and drainage dictate how you do it. Make sure the ground slopes away from the building everywhere. I normally maintain a minimum slope on the high end, about 1/2" per foot. On the low end, it is much steeper. That back/low end of my pole barn slopes away from the skirt at about 4" per foot. It's all fill brought in.

 

[s219]

Here's a view of an addition on my barn. Extra skirt added in the rear and sides, slopes up to just the standard skirt in the front.

 

[Doughknob]

Don't you have to put forms anyway to hold the #57 and sandrock inside? I'd be afraid to pour concrete with the rock below able to squish out the sides (while pouring plus over time.) So, might as well continue the PT skirt down to ground and now it is formed for the inside stuff.

 

[s219]

Don't you have to put forms anyway to hold the #57 and sandrock inside? I'd be afraid to pour concrete with the rock below able to squish out the sides (while pouring plus over time.) So, might as well continue the PT skirt down to ground and now it is formed for the inside stuff.

Depends, it can be stable if the outside backfill is stable. There is a lot less side pressure under a slab than people think. I've seen garage slabs on top of gravel base several feet thick and the gravel didn't squirt out. I think the key was that the base was wide and sloped gracefully away from the slab. Any ground pressure under a slab would propagate out along an angle of influence very much like that.

If pouring concrete, you can rake the gravel away from the skirt on the inside of the barn, and let the concrete flow down against the skirt to form a thickened edge on the slab and cap off the gravel. That will really help take pressure off the skirt boards.

 

[scaredychicken]

I'm learning here - thanks All. I like the new barn Drew.

My pole barn plans (30 x 40) are for next year - site prep and a slab will be the key starting points. Power and water. might even add a washroom while I'm at it, with composting toilet

but I'm trying to be practical without going over the top on budget ... big ideas

 

[Egon]

Skirt inside and outside with metal. Use gravel for fill against the skirting.

 

[DrewStyduhar]

Thanks for all the advice. Randy mentioned crushed concrete. I talked to the county and they would not approve that under the concrete slab..not that I really care for their approval (ha) but their reasoning wasn't very good.,......they just cited the fact that there can be junk in the concrete. When asked if I could simply pick through it to remove any junk, they didnt really know. Sounded well thought out! haha.

When talking to some other folks about a second skirt, they said the only way they would do this is if there was stone up to the skirt....inside and out. If dirt outside, they wouldnt waste the time since I guess even the ground rated stuff isnt very good anymore? Our dirt here has a ton of clay, doesnt really drain well and holds moisture so I guess that makes sense. The rock (including crushed concrete) wouldnt keep the second skirt wet?

scaredychicken - thanks for the compliment! Damn wood prices and all....it was do or die time. The metal carport style around here are very popular but I dont really like them. This barn has three ply lam posts and plastic sleeves. We ended up pouring the footers so they are HUGE. 24" diameter x 8" thick 4kpsi. They sent those precast cookies but I wasnt feeling it.

thanks!!!

Drew

 

[deezler]

Yeah the extra skirt board would eventually rot, but by that point you dont really need it anymore. It's not structural. That said, giving it a thin layer of gravel up against it wouldn't be a bad idea.

Yeah I don't think the county gets to forbid you putting crushed concrete under the slab. It would work great for that kind of compactible fill.

 

[DrewStyduhar]

According to the county, pouring a slab requires a permit. I can obviously fill it up with whatever I want but IF I get a permit to pour, they said they wouldnt approve the crushed concrete. told them I wouldnt be pouring until early next year so the pole barn can be finaled and not be tied to any concrete prep or fill work. Maybe the inspector was full of crap though? The slab would be floating so its not like its structural or anything. I called the soil/compaction guy that tested our fill and he confirmed the no crushed concrete thing. Said folks get around that by adding a few inches of #57 or crusher on top so the county doesnt know, haha.

I guess my point earlier about the skirt board is folks thinking it would last much longer with rock up to it compared to clay dirt. We have bad termites around here so I dont want anything in the ground rotting.

thanks,

Drew

 

[nyone]

Site prep is so much easier to do with no building in the way.

I would fill the outside first, grade away from the building and go from there on the inside. Do you plan on useing concrete underlayment?

 

[DrewStyduhar]

Hi guys,

Life got in the way but I'm back on this now.

I went to place my order today for the pressure treated wood (2x8's) for extra skirting and after the sales guy understood what I was doing he said he thought it was a bad idea. Curious to get some feedback on his thoughts:

- The second skirt will eventually rot and then you have a void where your 57 or fill under the concrete can wash into and you lose support under the perimeter of your slab

- You cant cover the PT stuff with tin.....even that nice painted metal, it will eat it up.

- He thought maybe you could roll/brush on roofing tar on the outside but couldnt vouch for that.

I wish there were some more composite lumbers being sold for a price that's not insane. I found a place online out of Maine that sells dimensional material made out of recycled plastic (MARKSTAAR). I would pay the price but their shipping is a deal breaker.

I put together a crude drawing in MS paint to show the fill I need. There is 15" between the sandrock pad and the spec'd finished TOP of the concrete. I plan to go with a 5" slab so figure 15"-5" leaves 10" of fill needed. The concrete guys want a few inches of 57 under the concrete but didnt recommend putting 10" of 57 as it would be too unstable. So figure 10" of fill - 3-4" of 57. That leaves about 6-7"inches of crushed concrete/crusher/etc. needed.

thanks,

Drew

 

[Midniteoyl]

Hi guys,

Life got in the way but I'm back on this now.

I went to place my order today for the pressure treated wood (2x8's) for extra skirting and after the sales guy understood what I was doing he said he thought it was a bad idea. Curious to get some feedback on his thoughts:

- The second skirt will eventually rot and then you have a void where your 57 or fill under the concrete can wash into and you lose support under the perimeter of your slab

- You cant cover the PT stuff with tin.....even that nice painted metal, it will eat it up.

- He thought maybe you could roll/brush on roofing tar on the outside but couldnt vouch for that.

I wish there were some more composite lumbers being sold for a price that's not insane. I found a place online out of Maine that sells dimensional material made out of recycled plastic (MARKSTAAR). I would pay the price but their shipping is a deal breaker.

I put together a crude drawing in MS paint to show the fill I need. There is 15" between the sandrock pad and the spec'd finished TOP of the concrete. I plan to go with a 5" slab so figure 15"-5" leaves 10" of fill needed. The concrete guys want a few inches of 57 under the concrete but didnt recommend putting 10" of 57 as it would be too unstable. So figure 10" of fill - 3-4" of 57. That leaves about 6-7"inches of crushed concrete/crusher/etc. needed.

View attachment 708490


thanks,

Drew

I added a 2nd skirt board to close the gap like 16yrs ago. Painted PT wood a few inches deep into the dirt No problems yet.