Outhouse Self Buid Questions About Height of DPC

[theskid]

HI all

I'm currently building a outhouse to use as a workshop gymn

I have laid 6 inch concrete trench foundations, with rebar added

I have currently laid concrete common for both leaves , 3 coarses high from foundations, and I have 2 questions:

1.Do I need to fill this cavity with concrete? as I was thinking of putting my inner leaf dpc 3 coarses high level with concrete floor and its dpm and have read there needs to be 225mm( 3 coarses free of cavity below the dpc),

2. The outer leaf is currently only 1 brick above external floor level so I was going to add 1 more coarse until I lay a dpc for the outer leaf ( to obtain the recoomended 150mm above external floor level)

So to elaborate the inner leaf dpc is at 3 coarses high, and the outer leaf dpc is 4 coarses high is this ok to do ? have the outer dpc 2 coarses higher than the inner leafs dpc?

Thanks for your time

[theskid]

Also wanted to add a third question but can manage tho edit original post

3.what thickness eps polystyrene is sufficient for under a concrete slab floor
I currently have allowance for20mm to leave a 3inch concrete slab,is this sufficient?

If anyone could kindly answer any of the 3 questions, Thankyou