Hello everyone,
I am planning a solid foundation for my garden shed, measuring 3 x 4 m (9.8 x 13.1 ft) with 5 cm (2 inches) thick walls. It will be used as a workshop. The roof will consist of sandwich panels and photovoltaic modules, so it will have some weight.
I spoke with neighbors who told me that there is a solid layer of sand starting at about 70 cm (28 inches) below ground here, on which everything is built. Unfortunately, the soil here is partly construction debris and earth, and due to space constraints, I have to dig everything by hand. Therefore, I am considering two strip footings along the 3 m (9.8 ft) sides, with a concrete slab on top about 15–20 cm (6–8 inches) thick. I have already excavated about 30 cm (12 inches), and on one side, I dug the strip footing down to nearly 80 cm (31 inches). Here it became clear that the soil suddenly becomes very solid.
Now my question: Is it sufficient for the slab foundation to be supported only along the 3 m (9.8 ft) sides down to 80 cm (31 inches) reaching the firm sand layer?
Here is a small drawing.
I am planning a solid foundation for my garden shed, measuring 3 x 4 m (9.8 x 13.1 ft) with 5 cm (2 inches) thick walls. It will be used as a workshop. The roof will consist of sandwich panels and photovoltaic modules, so it will have some weight.
I spoke with neighbors who told me that there is a solid layer of sand starting at about 70 cm (28 inches) below ground here, on which everything is built. Unfortunately, the soil here is partly construction debris and earth, and due to space constraints, I have to dig everything by hand. Therefore, I am considering two strip footings along the 3 m (9.8 ft) sides, with a concrete slab on top about 15–20 cm (6–8 inches) thick. I have already excavated about 30 cm (12 inches), and on one side, I dug the strip footing down to nearly 80 cm (31 inches). Here it became clear that the soil suddenly becomes very solid.
Now my question: Is it sufficient for the slab foundation to be supported only along the 3 m (9.8 ft) sides down to 80 cm (31 inches) reaching the firm sand layer?
Here is a small drawing.
Certainly, the effort is a bit high. But considering the soil we have here, I prefer to play it safe and have something that will definitely last forever.
What do you mean by base frame? That’s exactly why it’s about having a perimeter strip footing or just on the 3m (10 feet) sides.
Very few also have an insulated roof made of sandwich panels with photovoltaic modules installed on top. And the option to insulate the floor since a small air conditioner is also planned. At least I would like to have that possibility.
MachsSelbst schrieb:
Sounds like a lot of work for a 2-ton garden shed. Depending on how the base frame looks, point foundations or a perimeter strip footing might be sufficient.
What do you mean by base frame? That’s exactly why it’s about having a perimeter strip footing or just on the 3m (10 feet) sides.
MachsSelbst schrieb:
No one here has poured a concrete slab for their garden shed; most are on lawn edging or point foundations. I think one person actually poured strip footings... what an effort...
Very few also have an insulated roof made of sandwich panels with photovoltaic modules installed on top. And the option to insulate the floor since a small air conditioner is also planned. At least I would like to have that possibility.
M
MachsSelbst5 May 2026 12:17Then you actually need to excavate down to 80cm (31.5 inches), add gravel, and compact it. After that, dig and pour strip footings. Then place the slab on top.
If you make the strip footings frost-protected, everything beneath your slab must also be frost-protected. Otherwise, groundwater could collect there, freeze, and crack the slab.
But your garden shed should come with a foundation plan or you should be able to request one from the manufacturer. Only if you follow that plan will the manufacturer’s warranty be valid.
If you make the strip footings frost-protected, everything beneath your slab must also be frost-protected. Otherwise, groundwater could collect there, freeze, and crack the slab.
But your garden shed should come with a foundation plan or you should be able to request one from the manufacturer. Only if you follow that plan will the manufacturer’s warranty be valid.
MachsSelbst schrieb:
Foundation plan is not included. Also not in the instructions. I think it is primarily not intended to be provided.
Thanks in advance for your quick replies. Strip foundations along the 3-meter (10-foot) sides have already been excavated.
Everything else has currently been dug out about 30 cm (12 inches). I will continue to excavate this and fill it with gravel.
The question remains whether the strips on the 3-meter (10-foot) sides are sufficient or if they are really supposed to go all the way around.
M
MachsSelbst5 May 2026 13:08So, the foundation plan for my garden shed specifies laying 15cm (6 inches) of gravel on a load-bearing layer, followed by pouring a 15cm (6 inches) thick concrete slab with two Q131 steel reinforcement meshes embedded. You can probably skip the strip footing entirely in this case... there are even foundation methods for houses that simply involve placing the building on a gravel base. For reference, my city villa stands on a 20cm (8 inches) thick slab, admittedly with higher-quality reinforcement, just to give a comparison to the effort the manufacturer recommends for a modest 600kg (1,320 lbs) garden shed...
However, if you do decide to build strip footings, then they should be continuous all around.
What confuses me a bit is the procedure. Normally, you first excavate the footprint plus an overhang, then lay and compact gravel in layers, and then dig the strip footings into the compacted gravel.
That’s why I said I find it an excessive amount of work for a garden shed weighing 2-3 tons (4,400–6,600 lbs).
However, if you do decide to build strip footings, then they should be continuous all around.
What confuses me a bit is the procedure. Normally, you first excavate the footprint plus an overhang, then lay and compact gravel in layers, and then dig the strip footings into the compacted gravel.
That’s why I said I find it an excessive amount of work for a garden shed weighing 2-3 tons (4,400–6,600 lbs).
MachsSelbst schrieb:
I’m a bit confused about the procedure. Normally, you first excavate the base area plus the overhang, then lay a gravel base, compact it in layers, and finally dig the strip footings into the compacted gravel. This happens when you have no experience and just start 😉
MachsSelbst schrieb:
That’s why I said I consider it an excessive effort for a 2-3 ton garden shed. Is that referring to the strip footings being over the top?
M
MachsSelbst5 May 2026 13:16What kind of garden shed is that?
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