Mosman neighbours at war over a shared rooftop terrace in millionaire suburb

A bitter dispute about who has the right to use a shared terrace space between two neighbours in one of Sydney's most exclusive suburbs has escalated to the NSW Supreme Court. 

Marie Barter sued her neighbours Joshua Theunissen and his wife Michelle over an 'unfortunate' dispute about who has the right to use a 78sq metre terrace that sits between their two adjoining properties in Mosman. 

The two properties, which are estimated to be worth over $3million each, sit next to one another on the same piece of land after being split into two lots over 30 years ago.

Ms Barter can access the rooftop via a skylight and stair ladder in her 'battle-axe block', while the Theunissen's can access it via glass sliding doors at the back of their home. 

The court heard that on one occasion Mr Theunissen and his wife rang the police, alleging that Ms Barter and her partner were 'unlawfully intruding on the roof terrace'. 

They also alleged that Ms Barter's partner had assaulted Ms Theunissen. 

In response, both parties installed CCTV cameras on the roof terrace to 'monitor' each other's activity.

Ms Barter's legal action, first reported by news.com.au, sought to establish a 'declaration' that the Theunissen's do not have the sole right to use the terrace.  

The consultant objected to the Theunissen's allegedly placing netting over her skylight to prevent her from accessing the rooftop.

'Ms Barter also objects to the Theunissens placing various items on the rooftop, including a basketball hoop, an 8-seater octagonal table, two decorative blue ceramic vases, other pot plants and two gas heaters,' Justice Mark Richmond wrote in his judgment.

She also took issue with the Theunissen's son playing basketball on the roof terrace, which 'causes loud repetitive banging noises that Ms Barter hears throughout her house' and how the couple allegedly 'frequently played loud music from the rooftop'.

The Theunissen's argued that they were entitled to sole use of the roof terrace and that Ms Barter's skylight was only added later. 

'They contend that, were the rooftop to be shared, this would impermissibly interfere with their own right to use and enjoy the terrace for recreation purposes,' Justice Richmond noted. 

However, Justice Richmond ultimately ruled that the roof terrace was a shared space, suggesting it was possible the warring neighbours could both enjoy a 'drink on a summer's evening'.

'There is no reason in principle why each of them could not use the rooftop area for that purpose as it is sufficiently large for each to be able to enjoy it without unreasonably interfering with the use by the other,' Justice Richmond noted.

However, he ruled that both neighbours' CCTV cameras constituted 'actionable nuisance'.

Daily Mail Australia contacted both parties for comment. 

Legal costs between them will be decided at a later date.