We're getting plans+quote from a volume builder in Sydney (not signed with any builder yet), and after soil test they advised us that they would add a $7000 cost to upgrade from 20Mpa to 25Mpa concrete.
They have also added a note that piering may need to be upgraded to screw piers (currently we have fixed pricing in the quote for however many concrete bored piers are required) if soft or collapsing soils are present.
Firstly, I was just wondering if the concrete charge sounds fair enough? Does 25Mpa concrete incur other costs such as additional labour, other additional materials, etc?
I can see at http://www.eurekaconcrete.com.au/pricing that perhaps it would be $10 or maybe $20 extra per cubic metre (unless it's different in Sydney?), but I don't know the ballpark of how many cubic metres of concrete would be required.
Note that the total proposed ground floor area is 210m2 (approximately 22m long). This is a double storey brick veneer house, H1 class waffle pod slab. There's a dropped edge beam around the front of the house, ~50% of perimeter. Doing max cut 600 at rear, max fill 500 at front (land slopes upwards a little from front to rear).
From my layman's perspective, I would have assumed there would be much less than 210m3 of total concrete involved (that would require an average thickness of 1m) even if they need a few dozen piers to 2.5m or similar. I could be completely wrong though. $7000 is enough for $30 extra per m3 for 230m3.
Secondly, what would be reasonable ballpark figure to expect if the concrete bored piers need to be changed to screw piers? Perhaps that's a question that depends on too many site-specific details. Trying to research, I've seen people on this forum say a few dozen such piers added anything from $5k to 10x that.
Is this something that any builders would be able to determine before the existing house is demolished?
The soil test seemed to give no indication that there was soft or collapsing soil. The overall classification was P due to:
- a couple of trees within the zone of influence
- KDRB, and the current house is very old so there's no record of what was done with the soil (classed as uncontrolled fill). The guys doing the soil test reckoned at the time that it looked like natural soil (sounds most likely).
- the soil test in the backyard indicated low bearing (<50kPa) until it hit clay less than a metre down (150kPa at 1.4m deep). No issue with the test near the house.
Just as an indication, they've previously added:
- ~$13k for the dropped edge beams
- ~$26k for totally fixed concrete bored piering price + cut and fill + marine environment upgrade.
Thank you for any feedback or advice.