Drop edge beam vs retaining wall

Hello All,

Background:
I live in Sydney and will be building at Schofields in north western Sydney. My block of land is 15m X 30m fairly flat. The slope is about 1.1m from front to back, going downwards to the back.
There is also slight slope from right to left of land.

Situation:
1) Initially was planning to build a single storey house with McDonald Jones. They got a soil test and contour survey done for tender. The soil test results came back with M class slab and A1 soil and not saline affected. Since the building footprint had less than a meter fall, the site costs were all included as part of the standard inclusions. Only had to pay extra for piers IF they used more than 50 lineal meters at $90/meter.

2) Later decided to build a two storey house with Wisdom Homes. They also got the tests done, but the results are very different.
Wisdom say that I need H1 slab that costs $3850 extra and also I need drop edge beam plus import / export of dirt for the fill and an extra concrete pump at an extra cost of $9450.
Also they say that the soil is saline affected and will need a protective membrane.

Questions:
1) I'm very confused about which one to believe as the two results are in contrast in every sense. What do u think?

2) When I questioned the difference, the Wisdom consultant said that I can choose to remove the drop edge beam. Since at the deepest point the slab will be about 300mm above the natural ground and I should get a retaining wall after handover on either side of the lot instead. Does this sound legit?

3) About the type of slab, wisdom consultant said that MJH would go deeper pier and ask me to pay extra, instead wisdom are asking me to pay for the slab upgrade. Not sure how much of this I'd like to believe. Any thoughts?

4) over all, if I removed the drop edge beam and keep a M class slab I will save about $14K
Not sure if spending extra $14K is worth the additional strength the property will have. Could you please advise?

Thanks a lot.

Sorry for my long essay!

Regards,
Ajay

Just an update to those that may read this.

After a lot of calls and discussions with relevant people, I have come to below conclusion:
1) drop edge beam doesn't give extra structural integrity or strength. Just is a planning requirement so rest of the lot can stay at natural ground level.

2) my neighbor has already started construction and isn't using drop edge beams. This means I can also remove drop edge beams and fill up the lot to same level as neighbor so don't need retaining wall on one side.

3) MJH soil result had actually mentioned that my lot was classified as "P" (problem site) however if the land developer had placed fill in a controlled manner, then can be reclassified as M slab.

So I have requested to remove drop edge beam and keep H slab. Will save $10K for drop edge beam.

Wisdom consultant was right after all.

thx for sharing mate, my relative is having this issue too.

Thank you so much for this post. very useful and helpful for me. I know it is quite an old post but After reading this I find that I am going through exactly same scenario as you. My block of land is 15 x 30, at approx 20.5 AHD in marsden park and less than 0.5m of slope.

Developer: M class slab, A2 soil classification

Builder 1: M class slab, classification and no mention of DEB or deeper piers but their Tender is not fixed price and I may have to pay things letter

Builder 2 (Eden Brae Homes): H1 class slab, classification and significant amount of DEB on both side of property and deeper piers but their Tender is fixed price.

I am confused about whether to go with EBH or not as they seem to charging a lot of Drop edge beams where I may not need it as block of land is flat. However I am not sure If I ask them to remove, Council may ask me to put retaining wall later? I think it also depends on at what level builder cuts the slab, if they cut the slab lower, then DEB becomes a necessity.

What do you Reckon @ajayshekar?