ᐅ Foundation for an 18 m² garden shed

Hello

This is a garden shed (about 3 x 6 m (10 x 20 ft)) that requires a foundation. The shed is located practically in a field, making it difficult to use large amounts of concrete. The base is planned to be made from structural timber measuring 12 x 12 cm (frame 3 x 0.6 m (10 x 2 ft)).

Now the question is whether a "proper" foundation (80 cm (32 inches) deep) is necessary here, or if "concrete footings" alone would be sufficient. If a deep foundation is required, I can only imagine a pier foundation (digging holes with an earth auger and pouring concrete).

Thank you!

Then just do it that way.
Basically, you can probably only be sure with a soil survey. But for a garden shed, I wouldn’t make a huge effort. Just add two extra pad foundations, dig the holes with a sufficient diameter, and maybe even add some reinforcement steel.

Thank you, I think this is the safest approach. What spacing is recommended here? Of course, I want to minimize the number of individual footings. My concern is about the beams for the garden house floor, which might bend if the spacing is too wide. A slight bend is acceptable, but not too much (the garden house will be somewhat heavier as it will be insulated and clad with rhombus siding).

Well, it probably also depends on the thickness of the beams. For 8x8cm (3x3 inches) or so, I would have placed two on the short sides and three on the long sides. If you want to use narrower ones, you might need more.

So far, this is just theoretical for me; maybe a professional will chime in.

The beams will be 12 x 12 or 6 x 12. That would create a grid of 1.5 m x 2 m (5 feet x 6.5 feet). Online, you often see much smaller spacing (50 - 80 cm [20 - 31.5 inches]).

I think that is too close, but I don’t really know. Especially since the foundations are already 80 cm (31.5 inches) deep with a diameter of 20 - 30 cm (8 - 12 inches).

In this example, it only uses four as well, right? Well, that will be smaller.

You need shorter spacing if you want to lay the floorboards directly on the joists. These are usually not very thick and would otherwise sag. However, you can also add a cross battens layer over the joists to reduce the spacing.

In my opinion, with 12x12 you don’t need to worry; three on the long side should be enough. But I am not a structural engineer, nor a carpenter, and I have practically never done anything like this. So take this with caution.