Strange shed base situation - How best to finish???

[bryanchicken]

Noob, go easy
Hi all, im hoping for some advice on options for finishing a shed floor i have in my garden.

This is what i have at the moment:

Concrete base - approx 4 inches deep.
DPM on top of the concrete
Directly on top of the DPM is the wooden shed structure. Each wall has a tanalised (sp?) bearer, for want of a better/correct term.

So inside the shed the floor is basically the DPM. I would like to add a proper floor to this.
The concrete slab under the DPM is not very flat. Its level, in general but there are a lot of ridges/troughs.

So far, i have 2 ideas, but i have worries/questions about both:

Idea 1
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Fill the area inside the shed with some screed, approx 40mm and level it.
With that i'd be a bit worried about what happens if it expands in hot weather. Would the concrete expand and push the shed walls apart?

Idea 2
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Lay some timber (treated, not treated??) on top of the DPM to act as floor joists and then fix some plywood to them. I was thinking something about 2 inches high to match the 2x4 wall bearers.
With that i'd be concerned with movement, due to the underlying concrete not being flat. There will be some quite heavy stuff going in there eventually.
Also, do i need to worry about allowing air to circulate amongst the "joists" to prevent damp/mould etc?


I'm fairly proficient at wood work, but i've never mixed or laid a screed before.
I also believe the wood option would be cheaper. Rough dimensions of the shed are 3.6x3.6m


I'd be happy for other suggestions also.

Thanks for reading and the help!


(sorry for mixing inches and mm together )

 

[merlin50]

i use 3 x 2 treated with sterling board then put the shed on top, my shed is full of very heavy machines

 

[Captain5691]

Hi

I would go for the bearers under the shed, and a wooden floor i would also put the DPM above the bearers, as if its directly on the concrete floor then the bearers sitting on that it will allow water to sit under the wood for long periods of time.

So concrete then some sturdy bearers DPM on those and the shed base/floor on top of that, will last a life time....

 

[bryanchicken]

sorry, i didn't make this very clear.
The shed walls and roof are already in place. I can't place anything under it.

So if i was to got with bearers for the floor they would just be "floating" on the uneven DPM covered concrete slab.

Thanks for the help

 

[seasickstevie]

You could put 'pools' of self-leveler in the low spots, or simply plane some off your bearers where the high spots are.

 

[bryanchicken]

Thanks, that is an option.
So you think the wooden floor is a better option than concrete?