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--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.

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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.

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Cytorath t1_is6amb3 wrote

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

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--Ty-- t1_is6n8c5 wrote

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

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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.

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--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?

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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?

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CasinoAccountant t1_is6fnk8 wrote

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

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--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.

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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.

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mqudsi t1_is67bor wrote

Remind me not to take your advice on anything.

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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?

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Emergency-Wave-5335 t1_is62xd6 wrote

Step one: move 🤣

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--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.

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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.

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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.

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--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.

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jesseaknight t1_is881ow wrote

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

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st3ve t1_is62v5u wrote

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

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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.

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--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.

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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.

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