UKH

We need to install a shed (or small summerhouse) on our allotment and are a bit unsure on foundations.

We can get a levelled off piece of ground but it would be topsoil/grass. It’s at the bottom of a gentle slope so could be prone to being a bit wet, but unsure as we’ve not had it over a wet spell yet. Though we could dig some drainage in as it will all be cleared.

What kind of foundation would we need to install for, say a 3x3m shed? Ideally we wouldn’t go down the route of anything hugely permanent, such as laying concrete, but also want something that will last a while.

Any advice would be welcome!

Hi James,

  Use gravel grid. Filled with pea shingle, provides a level base and some drainage. You could put weed membrane under it to prevent anything growing through. Easy to lay and remove. 

Gwain

I've just installed what Gwain describes for a 8×10 foot shed, much easier than concrete and the guys who installed the shed said in many ways it was better. I dug the hole, filled it with a bit of hardcore (that I had to get rid of anyway), leveled with sand, put a weed membrane down then laid the grid on top and filled with gravel.  

Thank you - thats great to know! Will be much easier than other options, though still lots of wheelbarrowing!

I forgot to ask about a greenhouse too…

We already have a nice paved area that is 6x8 foot which once housed a greenhouse. However i think we would ideally have a larger greenhouse than that. Maybe 10 or 12 foot by 8.

The existing area is already raised, and due to the slope if we extended it we would probably have about a 30cm difference in height.

I wondered if it would be possible to put some big 4” square stakes in the ground for two corners and make a large wooden base that covers the old paved area, but is suspended above the ground onto the stakes at the other end. And then build a greenhouse on top of that. Though perhaps there would be a more sensible way to do it…

Use the plastic grid / pea gravel system suggested above. Consider how much bigger than the shed you would like the base to be. Test lay the plastic grid to make sure you have measurements right. Put in treated round stakes as they will go in straight, check for squareness and level the tops as required. Dig in treated gravel boards level with the tops and secure to the posts. Lay membrane. Infill with soil or material to the depth of the grid (or a bit less if you wish), check for levelness, lay the grid and fill with gravel.

The end result (before the requested bbq patio addition)

Where did you get the EcoGrid from if you don't mind me asking? I've got to do exactly this job over the next few weeks too.

They came as a package with the shed, but a quick search suggests they’re widely available. This was what was suppiied:

https://www.thegardenrange.co.uk/p/garden-base/shed-base/plastic-shed-base-...

I got mine from Wikes, allthough a third party supplied it. 

We were going to go down the route of gravel / plastic grid, but having bought some sleepers to build some planters / raised areas, have decided to use these, in a basic grid (garden room 4m x 2.5m) on a membrane, with gravel (which we already have). The sleepers cost £25 ea for 20 x 10cm x 240cm, and look as if they'll outlast me. 

Useful thread; thanks all.

I have a supplementary question: how would you secure the shed to the foundations, if using the gravel grid approach?

Cheers

Al

There are various proprietary bolts / shackles / fixings available. Depends on the type of grid being used; when i was shopping around looking at grids etc, most of them seemed to come with fixings, depending on the floor of the shed.

Thanks, will have a look around

Using the contents 🙂

We didn’t bother. as it’s a heavy thing in a sheltered position and not going anywhere. A year later, it’s stll there.

I guess being on the side of hill facing the prevailing wind close to the West Cumbriian coast doesn't count as sheltered 

To be fair it didn't move far. 

Unlike the greenhouse.

There are lots of replies about a shed base. For the greenhouse I went for a low (reclaimed) breeze block wall, which as well as something solid and rot proof to bolt the greenhouse frame to also adds a foot or so of height to the inside of the greenhouse, which is great for the plants and my head. 

I put a shed up for my dad (years ago, the day he moved into his last house which didn’t have a garage). I just dug out some turf and laid slabs to about 30cm more than the dimensions of the shed, with a weed proof membrane underneath. Some gravel or MOT type 1 might have been good if I’d had time but in the event the shed was still there and still dry 10years later. It was held down by its own weight as it was in the lee of some trees. Sometimes simple is best…

The problem with gravel and membranes is that the membrane simply stops any dust on the gravel from going through it.  Weeds then happily grow in that dust layer, and put their roots through the membane, making them impossible to pull up.  If you use gridforce to hold the gravel in place you can't hoe it properly either.  Gravel has to be really deep to remain weed-free, any seeds germinating on the membrane need to run out of energy before they reach sunlight.