Audit New Zealand has signed off on the Hundertwasser and Wairau Maori Art Gallery fundraising process.
Whangarei District Council chief executive Rob Forlong said the audit found the fundraising and underwriting of the building met the conditions set out in the council's binding referendum in 2015.
Prosper Northland Trust (PNT) was behind the two-year drive to meet the cost of the building, raising $21.7 million and surpassing the revised fundraising target of $20.97m - up from the original $17m due to earthquake proofing and other engineering needs.
Now those same pin-point precise engineering requirements - still at the lines-on-paper stage - look set to hold up the optimistic, promised start to building before Christmas.
"We are still working on the engineering plans for the site," PNT chairman Barry Trass said.
"We have to get this 100 per cent correct. Our intentions are to still get started before Christmas, but realistically, that might not happen."
After the site plans are finalised, the building project will go out for tender.
As part of its due diligence process, PNT commissioned engineers to conduct soil testing on site in 2016.
Revised costings released in March showed an additional $3.6m in engineering costs for seismic strengthening and $1.1m in increased construction costs.
The impact of the Kaikoura earthquake on Wellington had boosted the trust's motivation to ensure the Whangarei building could withstand seismic activity, in the rare chance that it could occur.
Earlier plans for the site were no longer considered adequate under revised engineering standards, Mr Trass said.