Pouring Foundations & Oversite Slab at the same time

[WoOt]

Starting a 10m by 4m single story extension in about a month, so just starting to think about foundations.

I've spoken to BC and he's advised a 1.2m trench is required. I have a guy with a digger coming round to dig it all out and I'm going to ask him to reduce the oversite at the same time as he's digging the foundations. Which makes a lot of sense for us as access to the site is time-limited.

I was hoping to also pour the foundations and the oversite in one go, as I require a pump and they're seemingly about 400GBP/day. I can't however figure out a) whether it's possible, b) how to do it.

Anything I've seen online suggest you need to build up to DPM first. I was thinking I might be able to shutter up to DPM level around the perimeter and fill the oversite that way. But no chance I'd be able to compact the sublayers on the oversite that way. Unless I shutter in between foundations and oversite slab, but I don't know if that's acceptable.

 

[^woody^]

Oversite for a timber floor? If its a problem just use gravel and a weed membrane.

 

[WoOt]

Wasn't planning on timber floors, but insulation under concrete, with a screed over the top once the central heating pipes were in.

 

[^woody^]

You mean a floor slab then, not oversite. No you can't pour this at the same time.