Liz Barry says she never would have put a granny flat on her Christchurch property if she knew how much the process would really cost.

When Liz Barry decided to build a granny flat for her 76-year-old profoundly deaf brother she was told the consenting process would cost $1500. Now she is facing costs of $23,000.

The Christchurch restaurant owner says if she knew what the costs were going to be at the beginning of the process, she never would have gone ahead with the build.

Barry approached the Christchurch City Council in late 2015 to find out what the costs were for obtaining a building consent for a portable granny flat she wanted to put on the rear of a property she owned in Hillsborough.

DAVID WALKER/STUFF Liz Barry is angry she was told consenting fees to put a granny flat on her Hillsborough property for her 76-year-old deaf brother,David Armon, would be $1500, when she is now facing costs of $23,000.

Her brother, David Armon, wanted to move back to Christchurch after leaving following the earthquakes. He was missing his friends and felt isolated in the small north Otago town he was living in.

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Barry was unable to find anywhere in Christchurch her brother could afford to live so decided a granny flat on her property was a good solution. She had expected to spend about $90,000, including the $67,000 cost to build the flat. However, the cost has risen to $114,548 after associated consenting costs skyrocketed to $23,000, including a $12,465 development contribution levy.

DAVID WALKER/STUFF David Armon and his dog, Sammy, have settled into a new granny flat on his sister's property in Hillsborough.

The levy is charged by the council when a development results in increased use of its infrastructure and facilities.

When Barry first approached the council, she said a planner looked at the information on her property and told her the cost would be $1500.

She has since had to pay the council $4310 in consenting fees for the land. She also had to seek a consent for the building from the Selwyn District Council, at a cost of $3500, because the granny flat was physically built in Selwyn.

She was then told through email weeks later that she needed to get a surveyor to measure flood levels because the property was on a flood plain. That cost $1839. She also needed to provide a covered space for a bicycle and parking for a car. Then she was told she would have to pay a development levy of $14,757. This was reduced to $12,465 because the property was under 60 square metres.

"I was shocked and flabbergasted," Barry said.

The granny flat was not yet on her property when she found out about the levy, but it had been built and paid for, so she was unable to pull out of the deal.

The flat was now on site and Armon was living there happily, but the council refused to issue a code of compliance until it received payment for the levy.

The whole process has left Barry feeling angry at the council's consenting process, which she described as "ill-prepared and mismanaged".

She wants the council to waive the development fee.

A council spokeswoman said the council had no record of the original call with the duty building consent officer and he no longer worked there so it could not confirm details of that original conversation.

She said the duty building consent officer line provided general advice only and was not an exhaustive advice service.

The council said it was important for people thinking about developing a property to engage experienced professionals for advice.

"While we try to keep our processes as simple as possible, there is still a level of complexity to navigate."

When asked what action the council could take if Barry did not pay the development levy, council consenting and compliance general manager Leonie Rae said the matter would be discussed with Barry.

"We are trying to see if we can reach a solution."

The building has been deemed compliant and has passed its final inspection, but it could be difficult to sell the property in the future without a code of compliance.

Heathcote ward councillor Sara Templeton said the council needed to be clear with the information it provided about consents and let people know about the other costs they could incur.

"We target information mainly for people that know the system."

She said maybe the council should look at reducing the development levy further for people wanting to build granny flats.

Cr Jamie Gough said he was concerned the advice Barry was given at the outset was inaccurate, but he was divided on whether she should be charged a development levy.

"The heart says no. The head says yes."

He said it was hard hearing stories like Barry's, but a line needed to be drawn in the sand somewhere when it came to charging development levies.