Inner leaf at ground level for oversite concrete?

[miked1]

Hi

To keep my garage oversite (175mm concrete) level with the driveway it will obviously mean pouring the concrete below ground level so that the finish is one continuous level from inside the garage onto the driveway.

I had expected to pour the concrete so that it bears onto the inner leaf that will be built to DPC level (min 150mm above ground level) along with the outer leaf, but the contractor doing this part has asked for something different:-

Instead he's asked that the inner leaf be left at ground level and he can then lay the concrete and fill the cavity with concrete at the same time (C25 mix). OK seems logical enough as inner leaf can then continue to be built up on this, but it raises a couple of questions..

1. Is it okay for the cavity infill to be up at ground level?
2. What about the DPM? I thought this had to be at the same level as the DPC? [which will be at least 150mm above gl]
3. If the DPM is at the DPC level and my concrete finishes at ground level, does this mean there'll be a DPM border all around the bottom of my garage?

Thanks and hope I've explained it clearly!

Mike

 

[noseall]

for fire regs reasons the garage floor needs to be lower than habitable by 100-150mm. to make sure the garage floor and the driveway are at the same height, most builders settle for 150mm below.
yes you will see the polythene dpm around the skirting of the garage. i have cut this off in the past with no ill effects or come backs from b.c.
i argued any solvent spillage such as petrol would dissolve it anyway!