Including contingencies and all historic costs, the total cost of the project will now be $64.4 million.
It was in line with other projects that had to manage the combined effect of Covid-19 on work time, staff availability and disruptions in the supply chain for building materials, co-chairman of the Sarjeant Gallery Redevelopment Advisory Committee, David Warburton, said.
"The unprecedented increases in material and equipment costs across the national construction industry have impacted on the project beyond the normal historic contingency allowances made for similar projects."
Project director Gaye Batty said steady progress had been made since work began in late 2019.
"There have been delays, but we have ensured wherever possible that we have kept the momentum going. There has been no idling."
The project team recently evaluated the situation with quantity surveyors, Batty said.
"Checks and balances are regularly applied to the project and all parties involved are committed to a careful and transparent approach."
Batty said despite the project team looking for ways to make up lost time, much of the work had to be done sequentially, to ensure the stability of the Category 1 1919 gallery.
Covid-19 continued to affect proceedings.
"We've had the site closed during lockdowns, Covid measures to implement onsite and delays in accessing materials. We've also had to lease storage facilities to mitigate some of our supply issues," Batty said.
"It's about maintaining cost disciplines and not letting what you cannot control affect what you can. We will be continuing the value engineering process to ensure every possible cost-saving is considered."
Sarjeant Gallery Trust chairwoman Nicola Williams said she was disappointed with the news, but not surprised.
"I assure the ratepayers of Whanganui that, once opened, the Sarjeant will be an outstanding regional facility.
"It will operate and deliver at the heart of our community and provide a vital contribution reputationally and financially."
The task now was to minimise any impact on ratepayers, while recognising the immense value of this project to Whanganui, McDouall said.
"It's important the community knows that the only financial commitment Whanganui District Council has made to the project was $5 million in 2015 through our long-term plan and a 2017 guarantee made to secure government funding.
He said at least $10 million spent on the project would be going to Whanganui contractors and "jobs for locals".
"It's projected to attract 22,000 additional visitors to our district annually, generating $11.4 million per year in additional regional spending."
Conversations were already happening with funding partners and "a concerted drive" to find the additional money was under way, McDouall said.
The Sarjeant Gallery development has received $40 million, or around 70 per cent of its total funding, from various government funds.
A further $9.6 million has come via fundraising from the gallery's community of supporters across New Zealand.
The Sarjeant Gallery is expected to open in April 2024, which will allow four months to move operations from the Sarjeant on the Quay - and install the opening exhibitions.
