Do I really need a concrete foundation for my garden shed?

July 20, 2014 7:17 AM

Just purchased a resin-viny Suncast Shed (model BMS5700). According to the manual it needs a concrete foundation, but I'm wondering if I can get away with just installing it on level ground.

When I first started researching sheds, a few months before I bought it, the Suncast website specifically stated that vertical sheds did not require foundations to be built. Since then, they've redesigned their site to remove this information. I based my decision to buy the shed on the fact that it would not require a foundation.

I understand that it's not too difficult to make a concrete foundation. I'm just wondering whether it really is all that necessary.

They list the option of a wood foundation as well but I don't really have a lot of woodworking tools or the space to use them.

This is a modest resin garden shed. The heaviest thing we would be storing in it would probably be a manual lawnmower.

posted by Deathalicious to Home & Garden (13 answers total)

Best answer: If it has a reinforced floor you'll definitely need something more level than a dirt foundation. The poly floor panels have to be pretty level and regular to work properly.

We put together a similar shed a couple of years back and made a brick foundation for it that has worked well so far.
posted by infinitewindow at 7:28 AM on July 20, 2014 [2 favorites]

Response by poster: A brick foundation might be a good option! What kind of bricks did you use? And did you put anything underneath them to keep them level?
posted by Deathalicious at 7:40 AM on July 20, 2014

I think this is probably all about step 5 on page 11 of the manual, 'Anchoring the shed to the foundation." It's tall, with a small footprint. They want you to screw it down so it doesn't blow over.
posted by jon1270 at 7:40 AM on July 20, 2014 [1 favorite]

Best answer: This is much more a function of the ground than of the shed. If you don't make a foundation the structure will be floating on the soil. If the soil is well draining sand below a thin layer of topsoil you are probably fine with stripping the top soil and putting down pavers to set the shed on. If the soils have clay (fines) then you really want something more stable - especially if you are in a climate where water freezes part of the year.
posted by meinvt at 7:41 AM on July 20, 2014 [1 favorite]

Response by poster: Jon1270, in another version of the manual for this or a similar product, they recommended driving 12" spikes through the shed into the ground to stabilize it. Would that work?
posted by Deathalicious at 7:46 AM on July 20, 2014

Best answer: I'd have no fear about putting this on a paver or brick base, or directly on tamped gravel, but it's going to need to be tied to something or it will blow away in the first storm. Are you going to back it up to a fence or the garage maybe, and could bolt it to that?
posted by Dip Flash at 7:57 AM on July 20, 2014 [1 favorite]

If you go with brick, you use sand to level it. Dig out the area, put in an inch or so of sand, lay in the bricks, smooshing them about into the sand, and add sand between them to keep everything in place.
posted by colin_l at 8:21 AM on July 20, 2014

Best answer: in another version of the manual for this or a similar product, they recommended driving 12" spikes through the shed into the ground to stabilize it. Would that work?

It might help, but it wouldn't be comparable to screwing it down to something heavy. In clay soils you'd get some benefit, but in sandy soil or soft loam it would be almost pointless.

I typically see sheds of this shape set up against a larger fence or building, like an outdoor closet -- not freestanding out in the open.
posted by jon1270 at 8:28 AM on July 20, 2014

Response by poster: Unfortunately it will be free-standing. If I could put it against anything it would be my neighbor's property which I'm not sure they would agree to.

One of my fears about setting up a concrete foundation is realizing after-the-fact that it's not in a good location. I'm not very good at visualization so I need to actually see something in place before making a decision about it.
posted by Deathalicious at 9:40 AM on July 20, 2014

You could build it, drag it around until you like where it's at, and then build the foundation last of all. It's a small slab, only seven bags of premix according to a concrete calculator, so it wouldn't take long or cost much but would give a lot of stability.
posted by Dip Flash at 9:48 AM on July 20, 2014 [3 favorites]

Best answer: Gravel and four ground anchors and you are fine.
posted by vapidave at 9:57 AM on July 20, 2014

Response by poster: I went maybe a little overboard. I'm pretty sure the plastic floor needed something solid flat and level under it, so I put concrete blocks on top of gravel and laid a piece of plywood over that.

I'm going to paint the exposed edge of the plywood to keep moisture out, and anchor the floor to the blocks using some long concrete screws.

The only problem is the plywood — I swear it was perfectly flat when I got it at the store, but at some point during the install we discovered it's curved in the middle, so the shed is a bit wobbly. I'm pretty sure this will be resolved once I anchor it down though.

And I'm pretty happy with the location of the shed now.

I'll have pictures of the shed soon, and of course I'll update over the next year to see how it handles the elements.
posted by Deathalicious at 5:40 PM on July 20, 2014

We've got an almost identical shed. It's on stone pavers with a 4" stone dust/gravel bed (part of our patio). It's been absolutely fine free standing for a couple of winters now. Hasn't moved at all, though it is up against a fence (but not touching or connected).
posted by bonehead at 6:31 AM on July 21, 2014