Bord Pleanála has refused planning permission on design and traffic grounds for two major residential schemes in south Co Dublin.
The move overturns decisions by Dún Laoghaire-Rathdown County Council to approve the developments.
The board upheld appeals against plans by Paramette Ltd and University College Dublin (UCD) to redevelop the former Smurfit Group headquarters site at Beech Hill, Clonskeagh, for 429 apartments and four office blocks.
Its ruling, signed by board chairman John O'Connor, said the proposed 12-storey block on an already elevated site would be "excessively visually prominent in the wider urban setting, and would seriously injure the visual and residential amenities of the area".
The large number of residential units proposed, that only 57 of them would be three-bedroom units and the high percentage of single-aspect apartments would also result in a sub-standard form of development contrary to proper planning.
Bord Pleanála also said the scheme would represent significant over-development of the site and generate more traffic on Beech Hill Road and Beaver Row, both of which it described as heavily trafficked and sub-standard.
"The proposed development would tend to create serious traffic congestion, would endanger public safety by reason of obstruction of road-users and would, therefore, be contrary to the proper planning and sustainable development of the area."
Bord Pleanála's decision was hailed as a major victory for local residents by Cllr Dermot Lacey (Labour), who was the only local public representative to lodge an appeal. He described the scheme as "outrageous", saying it had damaged relations with UCD.
He said the proposal was the result of a deal between the UCD authorities and a private developer "without as much as a cursory note to the residents most affected".
"Site notices were located about a mile and a half from the houses most affected," he said.
The lesson for UCD and Paramette Ltd was that all future developments should first be discussed with local residents.
Bord Pleanála also upheld appeals by local residents against the county council's decision to approve plans for 387 apartments and 20 terraced houses on the former Premier Dairies site on Whitehall Road, off Nutgrove Avenue, Churchtown.
The board said the excessive height, scale, bulk and mass of the scheme would be "unsympathetic to its setting and inconsistent with the established pattern of development in the vicinity . . . [and] would have an adverse visual impact on the overall neighbourhood".
Even as amended by the applicants, St James Development Ltd, it considered the density - at 52 units per acre - excessive in an area which lacked the necessary public transport facilities and other social infrastructure to accommodate it in a sustainable manner.
The board's ruling also cited the high proportion of single-aspect apartments and their generally small size. Development on the scale proposed would create traffic hazards as it would give rise to serious traffic congestion on the existing road network, in close proximity to an established school and in an area of narrow residential roads.
