An outbuilding within permit development

[Shlomi]

Hi there, we've just purchased a new property in enfield, north London. The garden has ample space but there seems to be the perfect spot at the back right by the corner fences to build a 15 sqm room out of timber, 2.5m high for my woodwork hobby. However, there's currently two levels of concrete, raised above the garden level, see pictures. There's an old shed on top of the lower part of the elevation but the second elevation must have had another structure which had been remove before. To get my maximum head height I will need to go down to the ground level below the concrete slabs. I am wondering why they made those two platforms elevated above the garden. My worry is that I may find something underneath which might stop me from executing my plans.. Also if I go down back to the garden level will it require rebuilding of the fence/s with my neighbours? I'm reluctant to do that. What are people thoughts? 

[ProDave]

I would tackle the issue another way.  The PD height limit is from "ground level"  Clearly there is a step in level between your harden and that of the gardens behind.  So I would just regard the upper slab as "ground level" and work from that.

 

If the ground level varies, then PD rules say you measure from the highest point.

[Shlomi]

Hey ProDave thanks for the answer. Should I double check that indeed the upper slab is leveled with my neighbour's garden? Also, the first step-up from my garden is a very uneven platform, so how do you go about leveling the two platforms?