Need advice on pole depth and pad prep

[Dstyduhar]

Hi folks,

We are just finishing up a pad for a 40x48x14 pole barn. Total size is about 50 x 60. The area where the barn is going is on a slight grade so one end of the pad needed about 2.5' of fill and the other end needed almost nothing. No money to deal with a retaining wall on the fill side so we plan to taper the pad off 3:12 to 4:12 and sod or lay straw or something. All the doors are on the side of the pad that needed minimal fill.

The barn will have laminated posts (6' of which is PT) and set on cookies.
I live in an area of NC where the inspector isn't very familiar with lam posts, cookies, radiant flooring, etc. so he has a lot of questions and Im getting minimal advice from him.

Two questions here:

1. On the side of the pad with 2.5' fill, I have concerns about getting the footing down into virgin dirt enough. The builder typically augers 4' in the ground, sets cookie and post on that which means the post will only be in virgin soil best case 4' - 2.5' - 6" (cookie) = 1 foot. We have option to get longer posts or auger deeper and pour a footer? We cant just set the standard posts deeper because there needs to be 2' of PT above grade.

2. Because the property is on a grade (~2.5%), I want to elevate the front of the building so I'm not driving down into it. My plan is to have them set the skirt so finished grade (concrete floor) is ~12" above the pad. This will likely result in me coming back after barn is up to add a second skirt below the first, put some tin over the skirts to keep water away and blending some #57 up to the base.

Any thoughts here? I can get posts 2' longer on PT side for ~20$ more each.

thanks!!

Drew

 

[kd3pc]

need to be below the frost line... that would likely be 42-48" in your area. The inspector would have the requirements for your needs in NC. I would go with longer posts and deeper holes. You might get 6x6" poles or 4x6" at least corners and every other post if you are worried about loads and lengths.

 

[Dstyduhar]

Hi,

Thanks for the response.

The inspector here had never heard of a cookie or a laminated post so you can imagine the sort of help Im getting.

The frost depth here is a foot, believe it or not. We are in the flat of NC, not up in the mountains. They seriously pour concrete footing for slabs only a foot deep, haha.

The posts are 3 ply lams. This is my first time building with lam posts and it gets complicated because you cant just say I want a "longer" post since part is PT and the rest is non PT. If you do, they typically only increase the non PT side and that doesnt help if you want to sink them deeper since there needs to be enough PT sticking above grade. I have the inspector coming out tomorrow to take a look. The plan is still to drill 48" or more to get into virgin dirt as much as possible.

thanks,

Drew

 

[Chris705]

OP - your plan sounds solid, my only question on #1 is did you remove topsoil prior to filling with your lifts of dirt? Going down 1’ into virgin soil would be fine if you removed all the topsoil. Would adding an extra cookie or two and angering deeper be a solution? I’ve done work in the Raleigh area and cost depth there was like 24” so I think your really going to be fine however you proceed on these two concerns.

 

[petebob]

Hi Drew! I am also building a pole barn (40x56) in NC (Orange county). I had to have engineer stamped plans to get my permit. I have about 30" of fall across my diagonal. I put the poles in first with two rows of pt2x6 skirt board and I am filling it with #57 stone to the proper grade. In my head anyway, it would be equally expensive to have someone bring in all that fill and compact in 6" lifts. I was also worried about how to bore a hole that deep. I did them with my tractor and had to get an extension for my auger to get down 4'.

 

[Dstyduhar]

Hi Chris,

Yes, he scraped off all the topsoil. The area where the pole barn is going used to be a pine plantation...about 10 years old. I had them all grubbed out 5 years ago which left a lot of low spots where the trees used to be. Looked like a battlefield, haha. I actually hand dug the sod out of all of the low spot and to verify there werent any roots left. Plus, it was less expensive since the grading guy didnt have to scrap down deeper. Hope that makes sense. My concern is that they might drill over one of these low spots in addition to the 2.5' of fill on the high side and we might be left with minimal virgin dirt. I think im being paranoid but really want to plan ahead.

PeteBob - Hey man! I'm here in western Reidsville. I had to have stamped truss drawings and that was it. The builder can go 5-5.5' with auger so I have some flexibility there. I like your double skirt board setup, thats my plan too...Im going to do it around the entire building though. When we built up the pad, we had to stop SOMEWHERE with the fill dirt. The goal with the pad was just to make a level area for the builder. I plan to have the builder set the bottom skirt 8" off this pad so I can add the lower 2x8 skirt after. The pole barn company specs their sidewall height from the middle of the skirt (top in my case). Then I'll fill building up with 4-6" of #57, 2" foam and then 4" slab. You know how the rains can be here so I want to keep everything elevated! The builder thinks I'm nuts for wanting to elevate the building this much but I think it will work out better this way in the end.

thanks for the feedback guys!!

Drew

 

[IamLost]

Drew I will take it that you didn’t go with the pre fab metal building after all. Would live to hear your reasoning why you didn’t go with that option and what your est cost per foot is on the pole barn. I live closer to Charlotte and im starting to look into building a shop for myself. Your input would really be helpful to me.

 

[rburke65]

I wouldn’t think that in NC the frontline is down 48”.

 

[jamaik]

I have to say, you made squaring up the building so simple that a math-idiot like me even understands! Now, if you'd only taught me geometry/algebra in high school, I might have been an astro physicist!

 

[dave_dj1]

As long as the cookie is sitting on virgin soil it shouldn't matter if it's 6" or 6' deep.

 

[larry_g]

As long as the cookie is sitting on virgin soil it shouldn't matter if it's 6" or 6' deep.

In a pole building there are a lot more forces on the pole than just vertical down. In a wind storm there is lift and lateral fores that have to be considered. During the build process the pole has to stand on its own for a bit and will not do it is if 6" in the ground.

lg
no neat sig line

 

[Coach James]

Drew, had the footings poured for my building a few days ago, not the same as poles I know, but I think they went down 28 inches. I'm near Carthage, about 30 minutes south of Sanford.

Coach

 

[dave_dj1]

In a pole building there are a lot more forces on the pole than just vertical down. In a wind storm there is lift and lateral fores that have to be considered. During the build process the pole has to stand on its own for a bit and will not do it is if 6" in the ground.

lg
no neat sig line

I guess I should have said "as long as the pole is backfilled to the 48" mark" as the OP stated he had fill. There are things you can do to a pole to prevent uplift as well.