ᐅ Garden Shed Foundation: Concrete Slab or Strip Footing?

Hello, I would like to build a garden shed using aerated concrete blocks with a pitched roof. The area is approximately 15 sqm (160 sq ft).

Now my question is, what kind of foundation do I need?

Slab, strip footing, or pad footing? Reinforcement?

The most important thing for me is the foundation. What should basically go into the 80cm (31.5 inch) deep excavation? Sand?

Thank you

Hello knock88
Form the foundation shell, place proper reinforcement, and pour the concrete. Remove the formwork, fill the pit with reconditioned crushed loadbearing (RCL) material (compact well in layers), then pour a 15cm (6 inches) slab foundation. Also use proper reinforcement here. This should last for the next 500 years.

Steven

Okay. Simply fill the excavation pit with recycled material and then install a conventional concrete slab.

How deep does the pit need to be, and how many cm (inches) of recycled material are required?
What about XPS insulation, vapor barrier, and separation layer?

Thanks

Hello knock88

I assumed the pit with a depth of 80cm (31 inches) is already there.
If not, it’s enough to dig the foundations to 80cm (31 inches) deep. Set up some formwork and pour concrete. Don’t forget the reinforcement. After removing the formwork, excavate 30cm (12 inches). Fill in layers of 20cm (8 inches) with RCL (road construction layers), of course only if allowed in your area; otherwise, use crushed stone. Compact each layer thoroughly. Then pour 10–15cm (4–6 inches) of concrete on top. The RCL or crushed stone acts as a capillary break. Install a good, rot-resistant membrane under the concrete slab. This would be sufficient for a garden shed. You can also put Styrodur (extruded polystyrene) under the slab, but then you should dig accordingly deeper.

Steven

Do I now have to dig a pit 80 cm (31 inches) or 30 cm (12 inches) deep?

Hello knock88

Build a strip foundation. It should be 80cm deep (31.5 inches) to reach below the frost line. Once the foundation is completed, dig a pit 30cm (12 inches) deep. Place the recycled crushed stone (RCL) in that pit, and then the floor slab on top.

Steven