The Strata Titles Board has turned down a penthouse owner's bid to keep timber decking installed on his roof and an air-condition ventilation unit on a wall next to his level 30 unit.

In judgment grounds released last week, it refused owner Sit Lam Kwong's applications, because the installations were placed on common property overseen by the management council of the Ardmore Park Condominium in Tanglin.

The board - comprising deputy president Francis Remedios and members Chua Koon Hoe and Raymond Lye - said "the position taken by the management council when not agreeing to (Mr Sit's) proposals for retention of the works was not unreasonable".

The case helped clarify the law in relation to condo unit owners seeking to use common property adjoining their units - such as ledges and walls enclosing roof space - for their own exclusive use.

The condo's management council had taken issue with Mr Sit after it found in 2014 that he had installed the timber decking over the the entire flat roof outside his unit, including the floor trap and drainage system.

The area was accessible to all condo unit residents via a common staircase.

Mr Sit claimed the parquet flooring had been installed because the original floor became slippery and dirty whenever it was wet.

He had also installed an air-con vent on the wall of common property, arguing that the penthouse ventilation system was inadequate.

As these were common property areas, the council advised Mr Sit it had no powers to give him permission to use the space and he had to seek approval at an annual general meeting.

Mr Sit suggested mediation to settle the spat, but the council advised him to put it to the general body.

At the annual general meeting in April last year, he failed to secure the 90 per cent approval required for exclusive use of the common space for more than three years.

He also failed to obtain a simple majority that would have allowed him to use the space for one year, as provided for under the Building Maintenance and Strata Management Act.

Unfazed, he applied to the board, taking the unusual step of asking it to declare that the installations did not amount to exclusive use of common property and claimed the council had failed to use its powers in not authorising the works he had done.

However, the board said it was unaware whether such orders had ever been made, or whether it had the power to make them.

Even so, they would not have been necessary as it found that Mr Sit was not entitled to them.

His WongPartnership lawyer, Mr Christopher Chuah, denied that the decking on the ledge involved common property as no one could physically access and use the ledge areas.

But the council's lawyer Subramaniam Pillai from Colin Ng & Partners pointed out that the certified strata title plans marked out the area as common property, which fell within the council's purview.

The board ruled that while the referred ledge with a parapet wall is not commonly accessible, its presence "provides for quiet enjoyment of the feature to all (unit owners)" and serves as a sunshade to the units below it. Hence the areas are common property.

The board also found Mr Sit had carried out the works without first obtaining council approval.

Mr Sit was ordered to pay $10,000 in costs and is understood to have been put on notice to remove the items installed.