Groundwork & Foundations

Digout just trenches first or trenches and oversite?

Anonymous user 09/03/2024 - 2.34 PM

We have to dig about 40m of foundations to 1meter deep, the oversite dig-out will be about 400mm (for sub-base, blinding, slab, insulation, screed). Is it best to: 1) dig the trenches first and fill them (we'll be stopping one or two courses below ground level) and build up to ground or DPC level before digging out the 400mm or 2) dig out the 400mm and trenches at the same time and then we could concrete 600mm of the trench up to the dug out oversite level and then put 400mm of trench blocks up to ground level. Digging the whole lot in one hit makes sense to me but a builder friend said it would normally be done the other way? Maybe the reason for the other way is just to get the trenches dug and filled as quick as possible before they start falling in/filled with rain, etc? We're on clay which is OK in the dry but a nightmare (sticky and slippery) in rain. Many thanks!