Piers for a wood shed

[Holzstapel]

I am hoping to build or at least start my wood shed this weekend. It's going to be built attached to my current shed and I will be replacing the roof on the shed and extending the new roof off to one side which will be my wood shed. It's going to be either 10x10 or 10x8 on level ground with an interior height of about 8'. The person helping me is saying that I should go with (6) 12" sonotubes for the piers. These 6 piers will be evenly spaced under the the wood shed. (3) on the far left, (3) in the middle and the remaining side will be resting on the concrete slab of my existing shed.

Are these piers overkill? I plan on stacking the wood as high and as tight as I can (roughly 5 cords). I also don't want to dig this many holes if I don't need to as the ground where i live is mostly rock.

 

[DougA]

I dug down 4' with an auger on my Kubota into rocky soil and dropped PT 4x4's with a bag of cement in each hole. Using piers is not the problem, it's the rocky soil that will cause the headache. I spent a few days doing my 12 holes and pulled out some boulders. IMHO, it's a wood shed, not a house and using 4x4's in the holes should last decades.

Another option is to go to HD and buy some concrete deck blocks instead. http://www.homedepot.com/p/Unbranded-8-in-x-8-in-x-8-in-Concrete-Deck-Block-55N1AN/206125490 The risk with these is that a very high wind will blow the shed over unless you anchor it properly. It's either that or dig.

If you have someone near you will a backhoe, that;'s the easy and fast way to make the holes.

 

[chazcarr]

I use the deck blocks. About 5 years now and no issues.

 

[Holzstapel]

I think it's safe to assume that this shed is going to be filled with wood most of the time and shouldn't have an issue with wind blowing it over. One side and the roof will all be attached to my current shed.

 

[Wood Duck]

One reason for the tubes or any other style of foundation for the piers is to prevent frost heave and settling. Can you dig down until you hit some rock? I wouldn't want to rest the piers directly on soil because the soil could settle or heave. Dig down to rock, or at least dig a foot or so and pour a bag of quickcrete in the hole to create a solid surface for the pier to rest on. That wouldn't be good enough for a house, but for a shed it'll be fine

 

[hamslam42]

Is the wood going to be supported by the piers? Or are the piers just going to support the roof and wall framing and the wood will be supported by the ground? If the piers are going to support the weight of the wood, that type of support might be needed. Wood is heavy...I estimated 24000 lbs for a 5 cord woodshed I recently built. In some of my early planning when I was thinking of pouring footers, I was going to use 8 18" footers (for a 6ft x 26 ft shed) , but then decided I didn't want to dig footers and went with the pier blocks or deck blocks, although I had to use a lot more of them because of the calculated load each one would carry. I used this calculator to help:
http://www.ideasfordeckdesigns.com/calculators/deck-load-calculator.php

It is a deck calculator but my wood shed was basically a deck with walls and a roof...and a lot more weight than a deck! Using that I was able to calculate the anticipated load for each support pier. In my case, the limiting factor wasn't so much what each support pier could handle...it was actually what the soil could handle. Mostly clay in central Ohio so I had to design for a soil bearing capacity of 1500 psf. I either needed to make each footing bigger to spread out the load so the soil could support it (that was the 8 18" footers), or add more footings to reduce the load each one was carrying.

 

[kennyp2339]

In NJ our frost line is 24" - 28", the idea is to dig down to atleast that level, or until you hit hard pack.

 

[firefighterjake]

Dig a few inches to a foot or so below the ground at my house and you hit ledge . . . for this reason I went with cinder blocks on the ground . . . haven't noticed the woodshed tipping or off kilter.

 

[xman23]

In PA they allow 2 car garages to be built on a floating slab. They do a lot of them with a gravel base and a cement slab. I wouldn't do it. But if you don't care if the roof gets a bit out of level, go ahead don't put in footings below the frost line.

 

[Shane Collins]

I'm planning on building a wood shed soon and I'm going with the concrete piers. It's a royal pita going down past the frost line unless you have access to a backhoe. I built a 24x14 shed for my in-laws a couple of years ago and dug all the sonotube holes by hand. Too rocky around here to do that again. I'll be going with the concrete piers and if/when it goes out of level I'll still be glad I didn't spend days and days of digging for the piers. If you're planning on building a floor to stack the wood on just throw in a few extra piers for support.

 

[Longstreet]

If you are going to dig, please use the sonotubes. The worst thing you can do is dig a hole, throw a post in it, and surround it with concrete. That literately is the worst possible thing you can do. You still have to dig, the 4x4 posts sits directly on soil (little support as they are thin), and the concrete holds water against the post. Urrrgggg, it still amazes me how many people construct with this method. They always say "We've always done it this way and it works." It's the same thing as people burning green wood because their father did it that way. Or not burning pine because it's dangerous according to old timers. Fools.

If you are going to dig, just pay a few dollars more and use the tubes. Then again, for a wood shed, I'm not convinced you even need them - the deck blocks are great and save the wood from having direct contact with the soil.

 

[Holzstapel]

Thanks for all the advice, I really appreciate it. I placed the order for the supplies to be delivered tomorrow. I included the sonotubes and will start digging on Saturday after I get the last load of leaves down to the dump.

The piers are going to support the wood deck and the roof so I feel better knowing everything will be built stronger. I also thought, if it ever comes to it, this wood shed can comfortably support a hot tub.

I will be shocked if I can dig down more than 24 inches without hitting a giant boulder. There are not many houses with basements where I live because of all the rock. I'll be sure to post some photos too.

 

[FTG-05]

One reason for the tubes or any other style of foundation for the piers is to prevent frost heave and settling. Can you dig down until you hit some rock? I wouldn't want to rest the piers directly on soil because the soil could settle or heave. Dig down to rock, or at least dig a foot or so and pour a bag of quickcrete in the hole to create a solid surface for the pier to rest on. That wouldn't be good enough for a house, but for a shed it'll be fine

This is what I did when I built my wood shed addition to my pole barn. Used a post hole digger, went down about a foot and hald, put some rocks back into the hole, packed them in, then a bag of cement and then the deck block on top of that.

Good luck!

 

[Isaac Carlson]

We live on gravel and rock. Getting down to 2-3 feet is not too bad. Getting to 4 feet takes all day. Dig down to something solid and call it good. The rock and gravel here makes everything solid anyway. Our ground here is 5,000+psf and I believe it. Nothing moves. We went down 4 feet for our fence posts (10 foot posts 6 inch diameter) and they will not move. I packed them in with nothing but the gravel and rock that came out of the holes. You can anchor a semi or tractor to those posts.