The grants for a new building have been under scrutiny this week as public servants were grilled over any links to the 2018 Wagga byelection and NSW Premier Gladys Berejiklian's close personal relationship with former Wagga MP Daryl Maguire, which was revealed at the Independent Commission Against Corruption.

Conservatorium board chairman Andrew Wallace told The Daily Advertiser that the organisation "absolutely" had not done anything wrong.

"We've followed all the processes exactly as required, there has been nothing corrupt or whatever," Dr Wallace said.

"There is nothing we have done that's outside of the advice provided by government."

The Public Accountability Committee's inquiry into NSW government grants heard on Monday that the Premier gave a "commitment" to fund the conservatorium's new recital hall complex in August 2018.

The government had already announced $10 million to move the conservatory to the former Roads and Maritime Services building on Johnston Street.

Department of Regional NSW Public Works Advisory deputy secretary Chris Hanger told the Parliamentary inquiry the money "has been reserved conditional on the business case meeting the requirements of being a viable project".

"We have not yet received that business case. We hope to receive it soon. The assessment will then occur," he said.

Mr Hanger told the hearing "the Premier made that commitment" when asked who approved $10 million for the stage two development of the recital hall.

Greens MLC and committee chairman David Shoebridge said the grants were "a political promise, seemingly without any assessment or even paperwork to justify it".

"There still isn't a business case for this project, it was literally pulled out of thin air to try and buy an election," Mr Shoebridge said.

"The bureaucrats made it clear that they reserved the $20 million as soon as it was announced by the Premier, the Arts Minister and the Liberal candidate in the byelection."

Dr Wallace said the business case for stage two of the development was due soon.

"We are reviewing the tenders for stage one, which is due for completion by the end of this year but may push to early next year," he said.

"The [stage two] business case is being done and we're looking forward to the results of that coming out in March. It is an independent business case, it's done at arm's length from us."

The Premier's office declined to comment.