10x20 Shed base materials.

Submitted by EnuqieuEsur t3_y2y1iy in DIY

I have a 10x20 shed getting delivered as soon as I have the base set. Sales rep told me to place on 3-4 inches off 3/4 crushed stone as the pressure treated runners it rests on are lifetime warrantied and will do best being on flat level ground with good drainage.

The site we are placing the shed is mostly level, no more than a few inches out at most.

I was going to dig down and level a perimeter of ground contact rated pressure treated beams as a perimeter to hold the crushed stone but with current lumber prices I’m wondering if I have a better option.

Would it work if instead of the pressure treated beams I used concrete retaining wall blocks? This looks to only be slightly more expensive and should last longer than the wood.

Edit: I appreciate all of the responses but I’m now more confused than when I started. For context, in MA, cost is not a huge issue as I’m ready to spend as much as necessary to do this right.

Edit 2: there are (4) 20’ pressure treated runners it is built on that it will sit on.

223

Comments

You must log in or register to comment.

--Ty-- t1_is5oy8t wrote

Lot of conflicting suggestions here so far.

You live in Massachusetts. As such, you experience freezing winter conditions. As such, you NEED a good foundation for your shed, or it WILL sink and settle.

What makes for a suitable foundation for a shed, however, varies.

Some people are describing a post-and-pier foundation, where you set concrete blocks or pavers at regular intervals, and then those blocks support your pressure-treated beams, which support your floor. I've built sheds like this. It is EXTREMELY laborious and difficult for larger sheds. Each and every single one of those concrete pavers needs to be set on a 1-foot-deep gravel foundation, which means you're digging a hole, compacting gravel, and setting a paver, like 50 times for a 10x20 shed, and every single one of those pavers has to be COPLANAR. It's so so so much more work than just digging out the entire area and filling it all with gravel that you just have to level ONCE.

So here's the foundation I'd recommend for a shed the size of yours, in your area:

Rent a skid steer and a clean fill dumpster.

Excavate the entire shed foundation down 12". Yes, 12 inches. You HAVE to remove the sod layer, that's absolutely non-negotiable, but for a 20'-long structure, I'd say a 12" deep foundation is the absolute barebones minimum depth.

Backfill with Crusher Run gravel (3/4" WITH FINES) to a depth of 2-3". Compact it. Then, backfill with 3/4 WASHED gravel the remaining 9", compacting it every 3".

Then, once you're at the top, lay out your screed rods, level them and make them co-planar, and then screed the top of the gravel pad to make it all perfectly level.

Then, put down some concrete pavers, spaced 16" between inside edges, running under where your beams will go.

Then, put down your beams, then shim them if you need to with PLASTIC shims.

Then build your floor assembly, then attach metal hardware cloth skirting around the entire thing, to keep out the animals that WILL nest under the shed. Then flair the skirting out, cover it with some excess gravel, and your foundation is done.

--

If you think this sounds like a lot, it's not. This is the barebones design of a "decent" foundation. It's not even a great one.

91

Cytorath t1_is6amb3 wrote

Overbuilt is a matter of opinion. Under built is a matter of fact.

16

--Ty-- t1_is6n8c5 wrote

"If it's worth doing, it's worth overdoing."

11

sparr t1_is5wa3f wrote

It's just 10x20. Settling isn't a big deal on something that small. Every few years you can lift a corner and put a new block under it.

7

--Ty-- t1_is64tgw wrote

I'm sorry but no. That's just a nonsensical suggestion. Casually lift the corner of a building to toss another block under it, trying to get everything flat and co-planar again, making sure to lift the pieces by whatever amount each footing sunk -- oh, and for the pieces sinking in the center of the building, you'll just have to crawl under the shed (hope you can fit in 5.5" tall gaps!) and jack the center of the shed up, I guess. Oh and then you gotta seal any of the gaps or cracks that opened up in the building envelope thanks to the differential settlement. OH and you have to do all this every few years!

​

Or, ya know.... just build it properly the first time around?

24

sparr t1_is67s50 wrote

Random 10x20 plans, first google result I found: https://myoutdoorplans.com/shed/10x20-shed-plans/

No center support. Why would you need a support in the middle of a 10ft span?

4

CasinoAccountant t1_is6fnk8 wrote

well you might consider it, if the goal was to do it right the first time.

6

--Ty-- t1_is6l8ep wrote

Those floor beams are spanning 20 feet, not ten. The joists are spanning ten, but since there's four beams beneath them, the span is reduced to 35 inches. The beams, however, are spanning the full 20 feet. If you just put a concrete block at each end, that's literally 18 feet of span.

In any case, even if it was only 10 feet deep, 4x4's can only span about 6'6" or so. 4x6s can technically span 10', but you'll experience a considerable amount of sag.

5

sparr t1_is6ner1 wrote

You're right, I didn't scroll down far enough. I only saw the higher illustration showing 10ft clear spans. It looks like that style, with four 4x4s under the joists, is really popular today. Every shed around that size I've ever built or owned or rented has had 2x6 or 2x8 for the 10ft span floor joists, without a center support, but they were all built 20+ years ago.

2

mqudsi t1_is67bor wrote

Remind me not to take your advice on anything.

5

itsnotwhatsbehind t1_is623w0 wrote

What if i want the same size shed but i live in florida and my yard just had 3" of standing water where i want to put my new shed?

7

Emergency-Wave-5335 t1_is62xd6 wrote

Step one: move 🤣

37

--Ty-- t1_is64ej1 wrote

Honestly, u/Emergency-Wave-5335 is right. Maybe not move addresses, but definitely move the shed. If you have a region that regularly collects standing water, then you simply can not place a shed there without doing massive soilwork to remediate the drainage.

You'd have to excavate down like 3 feet and replace all that soil with sand and other free-draining soils. Either that or re-grade the entire property to divert water from it.

You may be able to get away with building your structure like a dock, though. Florida's marshlands are used to that in home construction. Set posts 3' into the ground, and basically build a deck that supports your shed. That would certainly be easier than all the earthwork. However, the posts will rot out fairly quickly in those conditions, much like how the docks do.

11

duckdoger t1_is6wl1g wrote

You could take this a step further and use sonotubes and make concrete pillars/footings that are 4ft in the ground.

7

frzn_dad t1_is8ol15 wrote

Drainage doesn't help unless there is somewhere to drain the water to. When your whole neighborhood is underwater your choices are move or lift your house above the high water level.

2

--Ty-- t1_is8ot4r wrote

Yeah. I'm assuming based on OP's comment that it's just a portion of their yard that gets flooded, and not the whole thing. Remediating the soil will help, but if there's even more water to deal with, then yeah, it's just a losing battle.

1

jesseaknight t1_is881ow wrote

Good news: if he lives in Florida, most of the soil is already sand

1

st3ve t1_is62v5u wrote

The same thing, but you have to use metal shims instead.

1

TTigerLilyx t1_is6y95v wrote

You forgot ‘have a plan for the dirt being dug out’. If OP cant use it elsewhere, he needs to find someone who can take it off his hands or find a commercial dump. If the soil is good, everyone is looking for it to build raised beds, could even have them come and get it.

3

--Ty-- t1_is80nge wrote

Yes, that's why I mention to rent a skid steer and a clean fill dumpster. Clean fill (soil and other aggregates) often gets graded and re-used, rather than just ending up in a landfill with other dumpster waste.

6

poopgrouper t1_is910ua wrote

This is more or less what I did for my 10x16 shed, but I'd argue the gravel doesn't need to be that deep, and you don't need to bother with the different gravel types. Just get a couple yards of 3/4 crush, nestle some pavers in, level them as best you can, and call it good. If the shed settles a bit (which it will), the worst case scenario is that the doors stick. When that happens, jack up the corner that settled with a floor jack, stick some plastic shims on top of the pavers, and drop it back down. It's a 5 minute fix.

2

flyfriend333 t1_is615xr wrote

I am liitteraly doing this project this weekend. Here are the instructions, it's not complicated but does take some hard work.

https://www.siteprep.com/how-to-install-a-gravel-shed-foundation/

28

koselj056 t1_is62vpm wrote

I put in a 12x16 shed this summer and used this exact guide. I came here to post this link but you beat me to it. By far the most detailed information I found while researching best shed base options.

8

2drunk2remember t1_is93uh8 wrote

Funny because I've been looking into doing a project similar to this soon also.

The house i just bought already has a shed but it was just put on the ground with nothing underneath it at all. Unfortunately this has caused it to lean slightly. Soooo I need to do some digging and get a jack. Fun times ahead. I can feel it. Fortunately I have a life and dismemberment policy through work

Dont put your shed on just ground guys

3

TurkeyDinner547 t1_is5ec9q wrote

I'd level out some floating deck concrete blocks and call it a day.

26

Ok_Shop_3418 t1_is5l059 wrote

That's exactly what I did for my 10x12 shed. Worked great and holding up very well

9

Firehed t1_is5ovp6 wrote

Any tips or plans? I'm hoping to build a 10x12 once I figure out the details.

3

Ok_Shop_3418 t1_is5pymj wrote

You can use sand to help level out the cement blocks. Just get the measurements between the 4x4s on the bottom to make sure the blocks are spaced correctly. Use a 2x4 and lay it across the blocks to see which ones need to be raised or lowered etc. It's really not too hard, took me an hour to set mine up

4

the_flying_condor t1_is5z8x5 wrote

I just built a 10x12 lean-to style shed this summer (I drew my own plans with several variations and found the monoslope roof without any overhang to be the cheapest option available to me). My site is reasonably level naturally. I dug down about 6 inches and had a clean pea gravel fill dumped in the hole. I leveled out the gravel and then made a couple passes over the whole area with a vibrator to get some initial compaction. Then I filled in the low spots and did a bunch of passes with the vibrator to compact the fill as much as reasonably possible. This would not be considered a great foundation in NY, but for a shed I do not care if there is some slight settlement. For such a small structure, I don't expect there to be much settlement anyways as the whole area is over consolidated clay.

3

brock_lee t1_is5j4ps wrote

This is what I did. Was getting a shed and they would have charged a lot for leveling the site. Mine was about 6 or 7 inches out of level, so I dug down a little, provided them with level blocks in the corners, and a pile of extra blocks to use. They said that was perfect and once they had the base framing set on the corners, wedged in the other blocks on the sides and down the center to prevent bounce. These were flat blocks, not the ones that have grooves for framing.

5

Klaumbaz t1_is5pa9g wrote

I work for an extermination company.

I suggest putting it on a concrete pad, 6-12 inches wider around than the shed. Gravel/wood/cement posts, all end up being home to rodents living under it.

And remember to respect set back rules. Do not put it right up against your house or right up against a fence/property line. Make sure you can walk around it.

11

Sufficient_Top_4536 t1_is5exoj wrote

I recommend not placing on ground or gravel. Concrete blocks is a better choice. My blocks have sunk 4 inches, and runners now in contact, you don't want that.

If you live in a termite region treat the area just before delivery, you'll never have better access. Termites can bridge over pressure treaded runners and get access to untreated areas.

9

gaobij t1_is5s1ez wrote

You recommend concrete blocks even those yours have sunk to a point where it's now sitting on the ground anyways?

12

typicallydownvoted t1_is5sp3y wrote

Sounds like op who doesn't want lumber because it's too expensive so is thinking about concrete because it's only a little more expensive

3

Sufficient_Top_4536 t1_is5tv7k wrote

Yes, imagine where it would be now 25 years later. I should have gone higher

3

gaobij t1_is5vovx wrote

I'm mostly busting your balls. Concrete piers can certainly work. I think the real answer to improve your condition is to better prep the area with more compaction and different materials under the concrete plus maybe more piers to more evenly support the weight. Going taller just delays the inevitable.

2

Ichthius t1_is8hue7 wrote

Farm jack it up and put another paver or two on top. Repeat as necessary .

1

cbf1232 t1_is6gldd wrote

I'm in the Canadian prairies, so we get real winters. I built an 8x12 shed where the floor joists rest on two pressure treated runners. I dug down into the dirt and made a trench for each runner about six inches deep and 16 inches wide and a bit longer than the length of the runners. Each trench was filled with crushed stone, then levelled, and the runners placed on top.

That was 15 years ago, and it's still going strong. Haven't had any problems with warping/heaving/sinking, but it's possible we're just lucky with ground consistency here.

You'd likely get better drainage by making a raised gravel bed with pressure-treated walls, but that wasn't necessary around here as the water table is low enough.

6

ClickerMonkey t1_is5te4a wrote

Some people are misunderstanding what you're asking and some don't have experience with getting a shed delivered. As I've moved I've gotten sheds made and delivered and it sounds like what you are being told is what I was told as well.

I've done 3-4in stone as instructed and bordered with pressure treated. I've even used stacked pressure treated 4x4s as a retaining wall with large metal stakes going down through. That shed is 10 years old and the wood and shed are in new condition. It also helps that the siding is vinyl and not wood.

My latest shed was 12x20ft and the way they deliver and place those is pretty neat... But you definitely can't do what some are suggesting with placing them on anything but stones. Even a shed that large can be lifted from a single point of contact beneath it and spun around, it's wild. My shed though did have thicker flooring with joists every 1ft so I could park a tractor on it. A stone base that is 1-2ft larger than the shed is enough, that leaves 6-12in around the sides. I don't think you should have any concern with termites getting to the shed in those conditions. I would also consider whatever you choose as border - how it will be to mow around for example. My first shed had a nice border that sometimes stuck up too far (the land was not flat) so I couldn't easily mow around it, I had to weed wack it. My latest shed I only have a border on some of the sides because the backside goes down hill a few inches.

3-4in is enough, the sheds base they deliver will be plenty strong and rigid. If your base isn't perfectly flat they adjust the shed and push stone underneath the runners etc.

I would recommend getting huge pieces of thick barrier beneath the stone, that'll ensure nothing comes up from the bottom.

5

jabbanobada t1_is5tmgn wrote

FYI, also in MA, my shed foundation turned into a rat hotel. Killed the rats, bunnies moved in. I let them have it as nature abhors a vacuum.

Pay a lot of attention to what kind of critter hideaway you might be making.

4

Sam-Gunn t1_is84s08 wrote

>I let them have it as nature abhors a vacuum.

At least bunnies are cute. If you got rid of them you'd probably get snakes or wolverines or something.

2

Masterandslave1003 t1_is6b6rc wrote

I live in Canada and have had a 30x14 out building sitting in cinder blocks for 20 years with no issue. Each cinder block is no a 16x16 paver which is on a base of crushed compacted rock. I have it supported about every 6 feet around the perimeter. It gets down to -20c where I live in the winter.

3

kubotalover t1_is5jkuz wrote

I would just use railroad ties for a perimeter. I would first level it out. Lay down some geo-tech fabric then lay down the railroad ties secured in place with rebar. Then fill with 3/4” compact with plate compactor

2

PopeAdam t1_is5ud2g wrote

Concrete block and shingles between the concrete and wood

2

1northfield t1_is6a9gf wrote

Lots of advice on here and obviously some of it depends on you budget and climate/ground conditions. I would offer an alternative solution that may be a consideration depending on your priorities, look up a UK YouTube channel called Oakwood garden rooms and see how he does his rod foundation system (using generic supplies you should be able to get anywhere), very easy to do, very easy to level, will cope with almost any ground conditions but will be more expensive than some options, it’s at least worth watching to see how easy it is.

2

mickeysbeer t1_is77mpb wrote

Just build a concrete slab and give a 2-3 degree pitch.

2

rogerwa123 t1_is7hilz wrote

I had two sheds with similar treated runners. I’m in Minnesota so needed to make sure it didn’t heave. I dug 8 holes approx 30” deep, put out a leveling grid, and filled the filled the holes most of the way with class 5 gravel. I put some concrete blocks on the class 5 and leveled them against each other. The shed maker should have specs on how many supports are needed. I added a couple more. The shed is then placed on these blocks. 6 years and still solid as as rock.

2

BellyScratchFTW t1_is5l3fn wrote

You're wanting to put down ground contact rated pressure treated lumber for the ground contact pressure treated runners to sit on? Seems unnecessarily redundant. Especially if it's going to sit on gravel.

If you're in an area with a lot of rainfall and/or freeze/thaw cycles and want the shed to last a LONG time and never settle from where it started, I'd recommend taking the top soil up and then laying down the 4 inches of #57 (1/2" to 3/4"). Level it and compact it. Then you can either put the shed (with runners) directly on top of that or build it up more with concrete blocks if you like. Taking the top soil up is important because it's easily compressible. If you left it there's a good chance that your shed will sink a little, given enough time. But with those runners being pressure treated, they should be able to stay dry enough sitting on top of gravel.

What I'd be most worried about in my area is termites under there. They'll easily mud tunnel up to the shed from the ground. So if you're in a termite area, and most of the US is, I'd recommend treating (or having treated) the ground/gravel right before they put the shed down. Here's a map of the US termite zones if that helps.
https://www.termitestreatment.com/distribution-of-termites-in-usa/

1

EnuqieuEsur OP t1_is5ljah wrote

The pressure treated lumber was to build a perimeter to contain the crushed 3/4 stone.

I’m in MA so though there are no major termite concerns it is still something worth treating ahead before the shed is dropped.

3

BellyScratchFTW t1_is5nz9d wrote

Oh, glad to hear about the termites not being a big problem. I think the rest is just up to you. If you dig down the top soil (at least the grass layer at minimum), you'll likely have your 4 inches of perimeter right there.

If you chose to not take out the top soil, you have the option of extending your gravel "pad" by a foot or so all around. This will naturally taper off to grass and likely wouldn't be an issue later. But if you wanted a cleaner look, I'm confident that your idea of using pressure treated lumber or blocks would work well.

Your gravel will likely not put much pressure against the lumber or blocks and push them out.

1

pbpatty t1_is5ubc6 wrote

I use a/c pads. No prep needed if grade is flat. Then tapcon plywood.

1

billyiam5591 t1_is6nyxr wrote

I built my shed about the same dimensions 15 yrs ago. I 2x4 preframed the base with inside joists 16”” on center with blocking in between. I set the base on concrete pavers on the perimeter and some on the interior for additional support with 4-6” gravel tamped under each. Leveling pavers and setting base took some time to get it right bc my yard was sloped but not too bad. Still standing and solid. Live in MD

1

elusivem t1_is70m3t wrote

I have a 12x20, similar to yours my ground was mostly level. I dug out and flattened an area 1 foot bigger than the shed. I removed all the top soil down to the clay and compacted dirt and rocks, luckily this wasn't terribly deep for me, I think 8 inches or so. I roughly leveled it and rented a compactor to pack down what I moved. I used landscaping timber for the area that needed raised up, the areas under grade were left alone. Nefore i hadad my stone delivered I soaked the area it was going to soften the ground and used the compactor on it. It has been 2 years and it hasn't really sunk. I had some mild settling after the first winter, just had to jack one end up and move some stone around with a rake and I was good to go.

1

poofrt t1_is7ul8m wrote

This is what I did, 8x12 shed: https://youtu.be/WpAc64Op7MA

Hasn’t been long enough to say anything about the long term, but it seems fine so far.

1

shedbuilder84 t1_is7xfa9 wrote

What company are you buying the shed from?

1

EnuqieuEsur OP t1_is7xts0 wrote

It’s from a local old hickory dealer. 10% off in stock buildings at the local place pushed us over the edge as we were considering building ourselves. 20x10, 50 year warrantied smart panel siding, 50 year warrantied metal roof, 6ft double doors, 2 3’ windows for $7k delivered.

2

shedbuilder84 t1_is82620 wrote

7k is a good price for than much square footage. For that building it’s going to be delivered completely built. As for the base getting it level will be first priority. Depth is not as imperative. Ideally you wanna start at the high side of your spot dig down three to four inches and fill back up flush with grade. Then from there set to whatever it takes to make it level. In addition run a foot larger than the building all the way around. In your case this will be 12x22. By doing this your gonna make a drip line around the building. It will also allow for some wiggle room to get the building at just the right angle. One last tip if your delivery is after the first snowfall tarp the site before the snow if you have ever tried to shovel crushed stone you will know why.

1

Doctor_Frasier_Crane t1_is7xgpu wrote

Figure out where the runners are going to go and dig it down 4”. Fill with 3/4 crushed (no fines) 2-inches at a time and tamp it down. No need for a perimeter wood structure…you’re just digging a couple swaths of grass/dirt out maybe a foot wide…the surrounding dirt/grass should hold it in place.

1

LoganDredd t1_is8515u wrote

My shed is 12x20 and the area that put the shed wasn't level. So I used rail ties and built a 16x24 pad with crush and run in the center. I used 2 ft sections of rebar and drilled holes in the ties and hammered them through to anchor them into the ground. I used a full load of crush and run, 10 rail ties, and 30 sections of rebar. Leveled the area and have had no issues for 5 years now.

1

NoQuestion1969 t1_is8lc9y wrote

There’s a lot of great building advice going around here but I think the original question was, what can the op do to keep that gravel base together? The PT wood perimeter sounds good and would look nice but when I had one of these delivered when I lived in CT, I didn’t use anything. I suppose I could’ve gone with vinyl or metal landscape edging though. For what it’s worth, I was told by the shed company to have only a 6” base of gravel. In the 5 years I had the shed before I moved it was solid as a rock.

1

TheMattaconda t1_is8oozp wrote

If cost isn't an issue, I'd have 3-4" concrete foundation poured in advance. This will offer the best drainage, the best support, and the best lifespan of a prefab type shed.

1

EnuqieuEsur OP t1_is8ouuw wrote

What about a grid of 8 sonotubes with pressure treated beams running perpendicular to the runners on the shed? I think that’s our final decision due to frost line concerns in MA.

1

Beneficial-Shower-42 t1_is8qkd9 wrote

You're in Massachusetts. You must have municipal codes to follow and need permits I'm guessing?

1

EnuqieuEsur OP t1_is8qpvj wrote

Anything up to 200 square feet has no rules beyond placement away from structures and property lines.

2

Whiskeypants17 t1_is8szzw wrote

In my state it is 12 feet in any direction needs a permit, but every 'structure' no matter what still has some rules as you mentioned about property lines.

Anyway codes don't seem to care about what is under pt runners for accessory buildings in our area even though it freezes good, but they do care about adding earth anchors and straps to keep the thing from blowing away. To me the gravel under the runners is more about keeping the floor from rotting than frost heave issues. An uneven floor in a shed is easily fixed, but not a rotten floor.

1

Fishy-nice t1_is8xf5o wrote

I used theseon concrete patio slab on top of 0 3/4 rocks for a metal shed

1

Chris_and_Waka t1_is99qy5 wrote

Going to be doing this in oregon in about a month, I was going to just level out some dirt about 2-3x the size of the building, staple down some road fabric, and compact 3-4" of gravel ontop. Might use the abundance of large rocks I have to create a boarder after I get the shed placed

1

silverbullet52 t1_is5kgak wrote

I had treated timber as perimeter for my brick patio. After 25 years, most of them disintegrated. I replaced them a couple years ago with recycled plastic timber. I should have used plastic the first time. Not sure how prices are these days....

0