I basically owner built, my dad was a builder for many years so we did this together using his license. This mistake was one we came across far too late in the piece for anything to do about so we sought amendment. I wasnt involved in the original planning stage so we were not aware how important it was to the neighbour. When we found out, we sought many fair and reasoble remedies to ressolve the situation which obviously from the councils end they believed were fair too so they approved it. BCA standards are not an issue here, the house is only a single storey and we are well below the heights that may have meant we were encroaching on these standards.
I still feel sorry for you, but don't you think that pointing out that you and/or your Dad managed to build the house up to 1m higher than was approved was a fact that perhaps you should have revealed at the outset?
As I say, I still feel bad for you as I feel confident in your sincerity, that it was unintentional and you're doing everything in your power to rectify the situation, but it's much easier to see why the neighbour is so upset. Revealing this at the outset would possibly have changed the advice we gave, as it's probably wise to be far more accommodating of the neighbour than would otherwise be the case. My forecast of your neighbour's chances at VCAT has just been amended.
Firstly, do you have any comeback against your father's insurances for his negligence? I know it'd be uncomfortable suing your Dad, but builders have insurances precisely for just such a scenario, and surely your Dad would understand why you'd sue his insurance company, just as you'd make a claim against his car insurance if you were in a motor vehicle accident which he caused. If he's not covered by insurance and would bear any responsibility personally, obviously I can see why you wouldn't want to do that. But I think you need to investigate this possibility
now, because if this is possibly covered by your Dad's insurance, then 1) you may be able to avoid the stress of this whole drama by getting them to handle it, 2) they have probably been through all this before and can give you good advice as to likely outcomes and best way to proceed, and 3) you don't want to compromise your ability to claim by not involving them early (eg if you negotiate a settlement yourself where you have to pay the neighbour $10K compensation, they probably won't pay if they weren't involved in the settlement negotiations, even if they'd otherwise be liable.)
If your Dad's insurance company can deal with it, all well and good. If not, then my highest priority at this stage would be to seek some relevant cases which have come before VCAT in the past, and see how they were dealt with. If VCAT has usually held that Council is entitled to retrospectively amend approval without compensation to the neighbour, see if you can get a mediator to convince the neighbour of that, and persuade them to abandon their case. Perhaps offer some token compensation as a sweetener - a small bit of cash, a $500 nursery voucher for screening trees
, etc, and see if you can convince them that this is more than they'll end up with from VCAT after their legal costs.
If VCAT has frequently awarded compensation into the $10s of K, then see if you can get a mediator to settle it prior to VCAT for a reasonable compromise figure, taking into account that you'll both save legal costs, and you'll also benefit from getting your development finished sooner.
Obviously if the only thing that will make them happy is a 6m fence, or for your building to be demolished, then you've got no choice but to press ahead to VCAT. But I wouldn't assume that this is their intractable position without giving mediation a solid effort.
Good luck in negotiating this delicate path.