Digging digging, how much digging

[timothydoran]

I am at the groundwork stage of building a workshop. It will be 3x4m with a concrete base, a course of blocks and then 2x4 timber framed and waney edge cladding.

I have had an inspection dig and it is approx 350mm down to the hard stony ground. I have had two opinion on how much soil I need to remove.

Opinion 1 dig down to the hard ground at 350mm and then fill back with hardcore, mot1, dpm, concrete.
Opinion 2 dig down 200 to 250mm then mot1, dpm, concrete

Option 1 is the most work, most soil to dispose of, and requires more hardcore, but might be the safest option
Option 2 seems easier, quicker cheaper, but will it be as good.

In a cilla black style, which one of these enchanting options would you choose and why?

Many thanks

 

[motorbiking]

I built something similar. i went down 450. but probably over did it. I was insulating the base too.

 

[r896neo]

I would dig down and pour a strip footing, bring the wall up in block and pour a slab floor within. Trying to build on top of a raft will forever leave you with the problem of waterproofing the wall/slab junction.

 

[Doggit]

As it's predominantly a wooden shed, then a 4" slab would be sufficient. Option 2 should be sufficient, as the hardcore and mot1 are pretty much the same. But from your description, it almost seems as though you're dpm will be below ground level. Follow R896s suggestion, put down the mot1, some blinding sand, bring the dpm up the walls, and then pour the base.