Dún Laoghaire-Rathdown County Council has vetoed O'Malley Home's attempt to increase the number of apartments being built in the grounds of Traverslea, the listed Glenageary house built for Ivy Hone, the sister of artist Nathaniel Hone.
O'Malley Homes bought the 19th century six-bedroom house from its previous owners, developers Bernard Costelloe and Liam Maye, last year for an undisclosed sum.
The council refused planning permission for the proposal to add an extra floor to a previously approved three-storey over basement apartment block to create five extra apartments.
It said the revised layout would be of a poorer standard than the rest of the development.
Another reason for the refusal was that the proposal - which would have increased the number of apartments to 40 - would result in massing and overdevelopment of the site and would have an adverse impact on Traverslea, a protected structure.
In 2004 Costelloe and Maye were given the thumbs up by An Bord Pleanála for 35 apartments in the grounds of Traverslea despite local controversy.
The development was opposed by a number of parties, including An Taisce and Glengara Park Residents Association, which said it would destroy the outlook from the house and would be out of scale with houses in the surrounding area.
In July last year Maye and Costelloe got permission from the board to build three houses on the grounds and refurbish Traverslea and its coach-house and stable buildings.
The Irish Georgian Society had protested that the development would alter the character of the walled garden.
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