Mr Vallely said although his family were more interested in sport and music than visual arts, they recognised the importance of the Sarjeant Gallery to Whanganui.
"We see ourselves as quiet supporters of the gallery but keen supporters of the city and any organisation working to make it a better place," he said.
Sarjeant Gallery director Greg Anderson said the Sargeant Gallery collection was one of the biggest in the country and as large as the one held in Christchurch.
The total cost of earthquake strengthening the existing heritage building at Queens Park and construction of a new wing to house the extensive Sarjeant collection along with education and display facilities is estimated at $34.9 million.
Last year, the New Zealand government pledged $10 million to the project and the Sarjeant Gallery Trust needs to raise another $9 million.
Trust chair Nicola Williams said they were confident of achieving that target.
"We have seven individual pledges of $1 million and we are very grateful to people like you who recognise the value of the gallery to Whanganui," she told the Vallelys.
Redevelopment design drawings by Warren and Mahoney Architects have been prepared and are on display at the Sarjeant on the Quay temporary gallery.
Construction is expected to begin late this year with a two-year timeframe for completion.