It has been claimed that Sean Dunne's plans for a 37-storey tower in Ballsbridge would not contravene Dublin's existing planning policy.
But a hearing by An Bord Pleanála into the redevelopment of the Jurys and Berkeley Court site has also heard objections to the proposed high rise development.
Dublin City Council officials gave permission for an 18-storey tower with apartments, hotel and shopping centre on the site that Sean Dunne bought for more than €50m an acre, a total of nearly €380m.
But it refused a 37-storey building and ruled out office development because there is no zoning to allow it.
Town planner Tom Philips, who represents 44 individual appeals supporting Mr Dunne, said the tower should be allowed as it did not interfere with the city centre sky line and was comparable to the Heuston Gateway development.
He also pointed out that the planning board has the power to disregard zoning and allow office development.
Mr Dunne sees the 37-storey tower as being essential to the success of the scheme.
Scheme would destroy Ballsbridge: O'Malley
Danish architect Ulrik Raysse said the new development would create a city within a city that would rejuvenate Ballsbridge.
But local residents are objecting to the permission granted by the city council officials.
They say this decision disregards councillors who voted to refuse high rise and prime urban centre development.
Residents complain that the proposed buildings will be cliff-like, coming straight onto the pavement, and say existing water and traffic infrastructure will not be able to cope.
Former Progressive Democrats leader and local resident Dessie O'Malley said it would be a sad day if the destruction of one of Dublin's more attractive suburbs was allowed.
There are a total of 127 appeals in relation to Mr Dunne's plans for the Jurys Hotel and Berkeley Court sites.
The board hearing is expected to last two weeks.
