The planned high-rise skyline of Parramatta will need to be redrawn after a state government decision to preserve a public square from over-shadowing.

The former Parramatta Council had attempted to weaken rules preventing over-shadowing around Parramatta Square, the planned public heart of a city centre area set for a development bonanza.

But the Greater Sydney Commission, chaired by Lucy Turnbull, has over-ruled the previous council's attempt to weaken shadow restrictions, and imposed older and more rigorous standards that would preserve sunlight.

According to developer groups, this could have the effect of reducing the height of multiple towers planned to the north of Parramatta Square. It could cut them from a proposed 60-odd storey towers to 20-odd storeys.

The decision by the Greater Sydney Commission, and the response from the administrator of Parramatta Council Amanda Chadwick, raises an interesting potential outcome of the decision by the Baird government to sack councillors and replace them with administrators.

In this instance, the sacking of the councillors may have curbed the impulse of what had been a particularly pro-development council.

"I have and many in the industry have been quite surprised by the energy of various lord mayors for high-rise buildings," said Chris Johnson, the chief executive of developer group the Urban Taskforce, said of the previous Parramatta Council.

"They sent a message to the industry that they want high-rise buildings, and that the sky is the limit," said Mr Johnson.

"But the councillors have been sacked and I think a less robust vision of Parramatta's future is coming through," he said.

The decision to reimpose stricter standards about preserving public space from over-shadowing was made in response to the planned Greenway tower at 48 Macquarie Street, a block away from Parramatta Square, developed by Coombes Property Group.

The proposed 210-metre tower, which would have been more than 60 storeys, was recommended for approval by the former council after the council changed rules to allow over-shadowing at a portion of Parramatta Square.

The council's updated rule would have allowed shadows provided they passed within 45 minutes; previous rules had not allowed any shadows on a portion of the square during a two-hour bloc in the middle of the day.

The trouble with the 45-minute rule, however, is that it would have applied to individual buildings. And with multiple towers planned for the north of Parramatta Square, collectively they may have cast the entire area in shadow during the middle of the day in mid-winter.

Representing the Greater Sydney Commission, which has authority for large "gateway" determinations, Marcus Ray from the Department of Planning said the 45-minute rule should not be used.

Instead, the previous rule restricting any overshadowing should be revived.

Parramatta's administrator, Ms Chadwick, said she would take advice from staff about the impact of this decision on three proposed towers seeking planning approval.

"I can see that solar access to the square is an important community and economic issue, but I'm conscious of the views of former councillors and the importance of respecting their decision," said Ms Chadwick.

Ms Chadwick said she was also seeking advice on what capacity the council had to influence the decision.

Mr Johnson, who noted Ms Chadwick had not criticised the decision as the previous council may have, said mooted 60-storey towers would be cut back to 20 storeys. Taller towers would instead need to be built in different areas.

"This is likely to lead to a new shape for Parramatta's tall buildings," he said. "This is not the same image that Parramatta has been promoting."