Jul 23, 2021 11:40 am
I’ve bought two blocks of land and want to start my building with an underground element.
The goal will be to excavate, lay the slab, use concrete tilt panels for the walls, then cap the roof off with concrete for the next half of the home.
The block is of H1 composition and I’m trying to get roughly a (39 x 39 x 5) meter area excavated for an underground parking lot and theater.
I’ve not got much experience in this regard as I’m a software engineer by trade. What do you all suggest I looking out for when hiring a company to do this work or would it be cheaper to potentially hire someone personally for some period of time?
Would love to hear feedback to compare with local companies. At the moment I’m in lockdown at another state so no one is able to take a peek for an estimate.
Re: Excavation costs/tips2
Jul 23, 2021 1:30 pm
You roughly have 7600 cubic meters of soil.
One truck with a dog can move around 25 sqm of soil per trip.
So roughly you would need to plan for 300 trips. Depending on the location where you plan to dump your soil, you might be able to only like 10 trips/day, so you would need to hire truck and driver as well as excavator for 30 days.
Let's say you pay $800/day for decent size excavator + around $1000 for truck and driver rental - you spend roughly $1800*30=$54K on just an excavation cost.
You would have to retain what you have excavated, so you will be also paying $$$ for retaining walls, etc.
Re: Excavation costs/tips3
Jul 23, 2021 2:24 pm
Hi Alex, thanks for your feedback!
That’s a lot cheaper than I initially estimated! Excited to get “cracking” once covids eased up 😂.
Would you happen to have experience in what the concrete costs may end up being like? I’m guessing somewhere in the 350k mark with a reinforced slab.
Re: Excavation costs/tips4
Jul 23, 2021 10:06 pm
I’d get some plans and engineering first. There are lots of variables here. We just built a 12x4m cellar with Dincel walls. The footings were 450mm thick, slab between 250-300mm thick with many tonnes of steel in it. Waterproofing is difficult to get perfect.
I like the space but I do have some second thoughts and it is a really expensive and environmentally damaging way to get some extra space. Looks cool on grand designs in central London but we have a bit more space and cheaper land here.
Re: Excavation costs/tips5
Jul 23, 2021 10:27 pm
Well, the above is just a very rough estimate and in reality you might end with hiring at least 2 trucks + bigger excavator for continuity. So probably the actual cost of earthworks can easily be in the vicinity of $100k+.
Also digging in 5 meters into the ground seems to be too much, why do you need to go that deep? How is your house plan looking like?
40x40 m seems to be an extremely huge building envelope, are we talking about 1600 sqm single level house (or 3000 sqm+ if double level)?
This will cost you arm and a leg.
Except to pay 300k just for the slab and footings and piers.
Also, on such a big scale you generally do not use conventional building methods - I would recommend considering something like Cupolex slab with Radmyx premixed (https://www.radcrete.com.au/product/rad ... erproofing) into the concrete, so you don't require any waterproofing.
Consider Dincel for your retaining walls (doesn't require waterproofing too).
Also talk to Helixsteel guys, if you premix they fibers into the concrete you might end up with huge labour and cost savings on steel, only minimal reinforcement will be needed (https://www.helixsteel.com).
For your suspended slab you might want to consider Speedfloor system.
Although when excavated, Cupolex slab and reinforcement can be put together in half a day, with the slab size like this you might still need around 20 concreters + 2-3 pumps working on your pour at the same time.
Imagine spending 100k on just the concrete alone for your slab and footings.
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