Hopefully someone with some relavant experience can advise.

I’ve been collecting quotes for some groundworks. I’m planning a 6.5m x 12m beam and block slab, partially insulated and powerfloated finish, a 3.5m x 9m beam and block for a single storey extension (no finish for the time being) and installation of a sewage treatment plant with about 30m of new soil line to the system.

We’ve had two quotes – one was £35k (clearly didn’t want teh job from the start…)and a second was £20k inc VAT – is that reasonable? I don’t mind paying the going rate, but equally don’t want to have my trousers pulled down.

As a general rule all the works in construction, eg, plumbing, bricklaying, carpentry, etc, are highly predictable and hardly variable (I’m talking new build not conversion/refurb), the result is that pricing/costs can be fairly predictable and accurate. The big exception is groundworks which is hugely variable and unpredictable. It depends on a whole host of things some of which can be established by a site visit, eg, access, trees, drains, obstacles, etc, and other things which don’t always become apparent until the contract has been awarded and digging started. So expect groundwork companies to cover their arses.

I know bugger-all about groundwork pricing but someone who did would I suspect need a bit more information than what you have provided.

I did an 8x4m single story extension (well workshop, but same spec) and the ground works cost £5k DIY (hired some mates at £150/day), which means it would cost 2x that for some else to do it, so the £20k quote sounds like good value if you get walls and everything else….

Trial holes been done or are we just going digging? Depending on your ground v building inspector founds could be scary before you start.

Thanks for the thoughts – structural engineer was happy after a test hole revealed a strong gravel layer at 1.15m, with clay over. Beam and block is the order of the day to negate any heave from the clay. Access is as good as it gets.

We’ve got a few more quotes still to arrive, so I’ll see what shakes in a week or so.

So metre ish deep founds 600 wide with say 750 mass fill?
36 l/m in the big slab so days machine hire with driver. £300
To fill 16m3 ish c20 at prob 80/cube so £1300
Muck away or on site?
What brickwork/brickwork req’d to damp 450mm