How to build a shed foundation?

[Vincero1]

The Situation:

I have a pool equipment shed that is roughly 1500mm x 1500mm x 1500mm in dimensions. I’m hoping to replace it with an absconding shed from Bunnings.

However, the shed requires a concrete slab as a foundation. There are existing pole equipment fixed to the ground, and pipes and wires run underneath. I’m hoping to find an alternative way to build a foundation for this shed. 

The ask:

I’m hoping the solution is DIY achievable and not too expensive. I’d also like it to provide good drainage for stormwater, as the shed is located on the lower side of my property. The shed will be accessible and potentially store pool equipment and garden tools as well.

[Vincero1]

Hi @JacobZ, @EricL.

It took me a while to remove all three tree stumps in the area, and I started to understand more about the underlying pipe. There are four pipes going underground, plus electrical wire, and they seem to be heading in different directions. Since the location of the pipes is at the corner of an existing 1.5m x 1.5m pool pump box, there’s not much room for me to put in formwork and pour concrete.

If that’s the case, should I use concrete foundation blocks from Bunnings for the two corner areas that will be in the existing pool pump box? This would mean I’d have a 1.5m x 1.5m open area with two foundation blocks on one side filled with gravel, and a 1.5m x 1.5m concrete slab on the other side. The 3m*1.5m shed would then sit on the concrete slab, and the two foundation blocks.

Would that work? Here is the illustration below.

For the existing pump area, I’m thinking of using 100mm 10-20mm drainage gravel (https://www.bunnings.com.au/ki-carma-20kg-10-20mm-drainage-gravel_p3460052). I’d dig around the existing pipe and equipment, then use a hand tamper to compact as much as possible before filling with gravel. Do I need Geofabric, weed matt, or building plastic?

I’m also wondering what the ideal level for the shed should be. Since it’s between the boundary of my property and the pool, I assume it should be slightly lower than the paver around the pool, but still the same level as the rest of the land.

[JacobZ]

Hi @Vincero1,

As long as the shed is bolted to the concrete slab and the foundation blocks, and the crushed rock is compacted to support the bottom of the frame at the same height as the slab, I think this is a great solution.

I can't see any issue with your plan.

Jacob

[Vincero1]

Hi @JacobZ 

 Do I need anything other than gravel for the existing pump section? Like weed mat layer? How thick the gravel needs to be?

[JacobZ]

Hi @Vincero1,

With how thick the slab is, you would need to create a border around the outside of the shed to keep the stone in place. This could be done with timber sleepers and sleeper pegs, or something like garden edging with stakes.

It would be worth adding a layer of geotextile fabric or weedmat beneath the gravel. This will help suppress weeds growing through while still allowing any water that gets into the gravel to drain freely.

I'd aim for the gravel layer to be as thick as the concrete slab. Around 100mm at a minimum.

Let me know if you have any further questions.

Jacob