Pole Building footings

[rimshot]

I'm thinking about doing a pole building this spring. I have some trees to get cut down an tops burned. With the snow still on ground now is a great time for that stuff. I'll dig stumps out when frost is out of the ground.

I'll settle on a size later but let's fiigure something like 28' X 32'. This size would be the top end of the scale and it might even be down around the 20' X 30' range. I want the building as storage only for my trailer and maybe the tractor during the warmer months. I'm not going to have a concrete floor because it will just be storage building back in the woods behind my house.

I suppose I would space 4" X 6" wolmanized posts on about 8' spacing as specified according to the layout. So that means I shall need some concrete footings dug. This ground is all nice gravel ranging from pea stone to perhaps 8-10" diameter stuff. Post augers just don't work well here so being I have a backhoe I think I will just dig a hole down at least 42" deep to satisfy the local depth requirements for footing depth. I won't be forming anything so using the hole dug with the backhoe I will see to it the sides will be squared up so that I can just pour a footing of roughly 12" diameter an six to eight inches thick to center post on. If I have to I can drive a simple stake and shoot the grade level of the top level of stake as I pound it down and use this level to signal the grade of the top of the footing. Placement of course will be established with building lines and batter boards.

When I get all the footings poured with a helper, we can stand the posts on end resting on the exact building line marked on footing and brace plumb an back fill with a shovel until post has gravel backfill back to grade. At this point I should be ready to start nailing up skirt boards, and 2 x 12" for eventual truss application. Any suggestions or comments will be appreciated.

I'm retired so I can take my time and complete this thing.

rimshot

 

[DiskDoctr]

Hi Rimshot,

When I put in the 40' x 60' steel building here, I used 24" wide sonatubes. These are basically a thick cardboard and I think some plastic maybe. Looks like a giant empty toilet paper roll.

Dug holes for each post with backhoe, inserted and stabilized tube (cut to size with sawzall), and then filled in around to support. Filled these with concrete to level about 4-6" below the expected finished floor level.

We poured the concrete floor over top of these (which I understand you won't be doing this step), then used "earthquake anchors" (big concrete anchor/lags) to fasten our plates to the floor. A good, large hammerdrill works well to drill the holes.

We didn't need quite 24", but the concrete supplier had these as part of a mistake order and I got a deal.

The building has up to nearly 8' of fill at one end and about 1' at the other and it has never moved or cracked. I have 2 expansion joints, making 3 sections of 20' x 40' (also used wire and fiberglass mixed in).

The point is the pillars worked extremely well, even though the holes weren't very round as dug with the hoe initially. Maybe they can work for you?

Have fun and put in lots of lights on separate banks. T8's are best. And lots of plugs!

Hope this helps!

- JC

 

[rimshot]

Howdy DiskDoctr,

I would think 24 " diameter sonotubes would make a good form for this project. I wasn't planning on using any hardware where post meets concrete however. Since I have to have 42" from grade to bottom of footing I'm thinking of using your sono tubes an cutting them about 10 height. Then I can see to it each hole is compacted and cleaned up with a shovel.

The tube will be placed centered on the pole and I can drive a rerod stake shooting the top level to grade of top of footing. If I place the concrete within the form an keep it a bit lower that the top of the form I'm going to pump it once and regardless if the tube/form is slightly out of level the concrete should level itself. The building vertical posts can than be placed in middle of footing and plummed too the building line.

With nearly three feet of backfilled gravel around the post it ought to stay there. This should eliminate any need for me to use any of the hardware you had to use. I have used this method for pouring footings before and it works well in the right type of soil and ditches cleaned up by hand shovel. I hope my posts are straight it seems like this wolmanized stuff can really take off in the sun.

Thanks for checking in.

rimshot

 

[Diamondpilot]

Around here they just dig a hole 48" deep with a post hole digger, pour in concrete 6" and let it set up. The corner post get full concrete along with any poles at door opening but the rest just get stuck in on top of the concrete pad then back filled with dirt and tamped in.

Chris

 

[bobodu]

Building inspector told me to fill with gravel as it allows water to weep out the bottom into the soil and that they no longer recommend cement because water settles around the bottom of the post. He said to nail small scraps of treated 2 x 4 near the bottom of the post to help prevent frost heave.

 

[rimshot]

It's kind of interesting to see so many variations different folks utilize. Using the concrete seems to hold some appeal for me if for no other reason than to serve to spread the weight. If a person took a 1 5/8" X 7 5/8 x 15 5/8 concrete block slab and cut it in half placing the cut block between footing and post he could get that post bottom up off the concrete footing and then the water damage would be minimized .

rimshot

 

[Duffster]

I wouldn't worry about water on the bottom of the post. Posts rot at ground level where they get water and air.

 

[DiskDoctr]

I wasn't planning on using any hardware where post meets concrete however.

Hey Rimshot,

You may want to reconsider this part. Buildings tend to sway and move with weight, wind, snow, frost, etc. They can also LIFT We don't often think about that here in NOT hurricane or frequent tornado strike country, but it does make a difference.

Some sort of bracket that would hold the bottom of the post in place and anchored to the concrete would definitely be recommended (maybe even required by code?)

I heard for the first time around here that in order to refinance a mobile home, my friends had to buy and install a cable and bracket tie down system before the loan would go through.

Just watching your back

- JC

 

[QRTRHRS]

Does your local code allow precast footings? Usually cheaper than bringing in the ready mix truck maybe not so if you have a mixer. Just tamp the ground first.

As suggested, you need to limit post uplift. For windy sites, put blocks on all four sides of the post. The blocks should be treated for ground contact. They should be the same width as the posts and about eight inches long. Predrill the holes else they will split over time. Galvanized angle iron will work as well but use stainless fasteners.

By the way, all of your fasteners should be rated for ACQ or CCA contact, which ever type of treated posts you are using.

 

[QRTRHRS]

Hey Rimshot,

You may want to reconsider this part. Buildings tend to sway and move with weight, wind, snow, frost, etc. They can also LIFT We don't often think about that here in NOT hurricane or frequent tornado strike country, but it does make a difference.

Some sort of bracket that would hold the bottom of the post in place and anchored to the concrete would definitely be recommended (maybe even required by code?)

I heard for the first time around here that in order to refinance a mobile home, my friends had to buy and install a cable and bracket tie down system before the loan would go through.

Just watching your back

- JC

I never heard of anyone using a bracket to secure a post to a concrete pad with polebarn construction? I have seen "L" shaped brackets holding post frames to concrete foundations.

 

[DiskDoctr]

I never heard of anyone using a bracket to secure a post to a concrete pad with polebarn construction? I have seen "L" shaped brackets holding post frames to concrete foundations.

Being steel, it was easier for me as the brackets just bolted to the steel posts, then the long anchor bolts into the concrete. Not sure of the distinction you seem to be making between the term "bracket" and "L shaped brackets" ? Maybe I just missed something

We floated our slab on top of plastic, then 4-6" gravel, but the footers for the posts all had to extend below frost level. I think ours are all 48" plus. Some were 6' (where most of the fill was).

I see the OP is in Michigan, also a cold state (sometimes )

Hopefully a few building contractors/experts will chime in.

Rimshot- if you are going to put just a gravel floor in the building, you may want to put down fabric first, to keep the gravel from making its way to China We use plastic when under concrete- keeps it drier and warmer, but not sure how that would be for gravel...?

-JC

 

[DiskDoctr]

Here's a link with some pole to foundation options:

Perma-Column | Permanent Foundation Systems
Foundations - National Frame Building Association
http://postframeadvantage.com/i4a/forms/form.cfm?id=29&pageid=3931&showTitle=1

And I read some places using a type of coating (pvc or others) on the bottom of posts to prevent rot.

Hope this helps!

- JC

 

[rimshot]

I see what you are talking about now DiskDctr. That is one fine foundation system. I really like those tubes for the vertical stuff. The fabric or visquine is a good suggestion also. I don't believe thee 22A gravel will migrate too far as the grade will all be very nice native gravel (coarse)

I just got off the phone with the Bldg. Inspector and he wants trusses w/combined load of 70lbs/ft. Footings must be 42" deep from grade to bottom of concrete. There is no requirement concerning mechanical fastening of post to footing. I am in a very protected area of woods and the East side of a steep hill so high winds are not a problem. I understand the nature of the extra resistance for any wind lift.

Being that gravel is very coarse I would expect needing 20-30 yards for a 6 or 8" base of 22A crushed gravel. I could very easily provide a layer of 6 mil between the native gravel and the layer of 22A. With no floor and a steel roof I would sweat the sweat that forms under steel roof panels Spring and Fall. Creating ones own rain storm is the type of thing I am hoping to eliminate.

Qrtrhrs; Do you mean attach blocks of 2 X 6 perhaps of 8" length on four side of bottom of a 6 X6" post.. I'm not quite clear on your method. I believe you are trying to create an 1 1/2 surface to fight this wind lift.

rimshot

 

[Eagleview]

Why not just dig the holes and sit the poles in the holes with a punching plate at the bottom and back fill ? A bit of cross bracing in the walls and it will stand for a lifetime . Punching plates can be flat rocks , broken concrete etc . I used old truck rims filled with concrete and lowered into the holes when I built my house . The local concrete plant filled them for a carton of beer when they had left overs from jobs .

 

[DiskDoctr]

Footings must be 42" deep from grade to bottom of concrete. There is no requirement concerning mechanical fastening of post to footing.

A true "pole building" has the poles buried in the ground and wouldn't necessarily need any anchoring other than the concrete or whatever you used to fill around the poles.

But a lot of folks are putting in buildings without the buried poles, instead setting posts on top of footings (like my steel building).

If you're going to bury the poles (including within the sonotubes), you may want to consider putting tar and/or something to protect the wood below grade. One place mentions using tar, then a heavy kind of shrink wrap or other coating...some options there.

If you're going to set the posts on top of the footings, I would fasten the posts with anchors.

I'm not sure of your conversation with the inspector, but you might want to be sure he knows which method you are using. May not matter, but you don't want any surprises after it's built and to be inspected.

Sorry if it sounds like I'm being **** about this, but asking a few questions, maybe more than once to be absolutely clear, is better than remediating a misunderstanding later

You may want to ask for more info about the plastic under the gravel due to humidity. Fabric would allow water to pass through (both ways), plastic may hold humidity in the building due to exposed steel surfaces. Might want some opinions on that. Maybe tyvec has something that passes moisture one direction (out)...?

My steel building is fully insulated, but I recall the mfgr asking if it would be insulated. If not, he was recommending ventilation fans to manage humidity. Wouldn't be a bad idea either way.

Hope this helps out a bit.

- JC

 

[QRTRHRS]

Qrtrhrs; Do you mean attach blocks of 2 X 6 perhaps of 8" length on four side of bottom of a 6 X6" post.. I'm not quite clear on your method. I believe you are trying to create an 1 1/2 surface to fight this wind lift.
rimshot

Yes, that is what I am saying but keep the blocks up a bit from the concrete pad, perhaps six inches. You don't want to increase the surface area where you may have moisture.

What you are doing is making a rough "bell" shape.

 

[rimshot]

Thanks to DiskDoctr and QtrHrs. I appreciate your excellent observations and sharing of experience.

This building site is blessed with excellent natural gravel plowed in here by the glaciers they tell me. It's the same thing practically as placing a building over a never used drainfield only I am fortunate to have about 50' of natural God Given nearly pure stone.

You both have pointed out that it would be best if the post end grain is prohibited from wicking up any water. It would do exactly this if it were unsealed and rested on concrete directly. I don't recall if those sleeves on DiskDoctr's foundation are encased on the bottom or not. You built a Cadilac of a fine foundation. I'm probably going to have to do something a little more like a Chevrolet. I just don't need a Toyota. I would prefer the Cadilac of course but I want enough money in my budget to complete the steel roof

I talked to Lowe's and HD today and will be getting quotes of a 28 X 32 X 10' building. I did manage to upgrade the post material from the 4X6 posts to the newer laminated versions that resist twisting. Seriously, I have seen some regular wood version that looked like corkscrews.

One more quick question. What did you guys use for the load bearing connection at the point where the double 2 X 12 truss carrier's cross with the top of the 4 X 6 posts. I have seen guys simply nail those and I just cringe t the thought. Seems like they need more than nails can offer like possibly a couple of 1/2 " carriage bolts at the very least.

Again, special thanks to DiskDoctr and QRTRHRS for helping

rimshot

 

[bill in ny]

on my new pole barn i nailed the 2x12 truss carrier's to the poles. under each joint there is a 2x8x3' piece nailed for more support. the pole barn i built 28 years ago, using the same method is like the day it was built. i also nail a 2x8x4' piece between the carrier and the poles.

 

[DiskDoctr]

On my metal building, I don't have regular trusses, rather clear span beams. It's open to nearly 16' in the center.

That's the nice thing about forums. Lots of different advice from different people. :licking: (<-- Okay, just wanted to try this guy out!)

- JC

 

[dodge85rc]

Well on my pole shed and the addition that was put on, they used an auger to drill the hole 5 ft. down, below frost level, threw in a round concrete block and set the post in and back filled and tamped it in. This is how it is normally done around here. They used treated 6x6's on the posts, 8 ft. center. The posts are notched on top and the truss's are set in the notch. I think you guys are over analyzing it. Keep it simple. Don't laminate posts or wrap them in anything. If you buy a quality treated post of the appropriate size, rotting, water and structural integrity will not be issues.