The Oberoi family, based in Griffith, was seeking to extend their house to add a bedroom and accessible bathroom to provide for 79-year-old grandmother, Asha Chopra.

The block under discussion measures 1070 square metres and features a 355.7 square metre house,

Sabeena Oberoi said their extension application was rejected twice and they were told by the ACT Planning and Land Authority to consider putting their grandmother into a retirement home.

She said she first contacted the department with their request in October 2013.

"A staff member said to me: 'One has to make hard decisions in life, my mother is in a nursing home. You need to think about that'," Mrs Oberoi said.

"I want to keep my mother with us.

"There's no one there for her besides us ... my mother would die if I sent her to a nursing home."

She said the application was rejected twice by the authority on advice from ACT Heritage, despite reports from medical professionals, architects and builders stating the renovations were necessary and suitable.

But an Environment and Planning Directorate spokeswoman said the application was rejected on advice from ACT Heritage because it took up too much space on the heritage block.

Planning regulations only permit homes to cover 27.5 per cent of the block, and the Oberoi's existing home already occupies 37 per cent of the block.

"The ACT Heritage Council did not support the development application as the proposal failed to meet heritage requirements of the site coverage and planting area," she said.

Mrs Oberoi said invasive personal comments were made about her family, including asking why her children didn't move out and if her mother really needed a double bed.

The spokeswoman said the questions about the family's circumstances had been made because the authority believed there were design options that would accommodate everyone without an extensions.

"I'm the only child of my mother here in Australia, so my mother is totally reliant on me," Mrs Oberoi said.

"She can go nowhere."

The matter went to mediation, with no outcome. It will be heard in the ACT Administrative and Civil Tribunal this month.