The expansion would be a two-stage programme. The first would see three courts built, hopefully in the 2018/2019 year. This stage was expected to cost between $6.5 million and $7.5 million.
"And then two years later we'll go to stage 2, which will be another two courts we think that will cost about $4.5 million to $5.5 million," he said. The costings for both stages did not include amenities, or car parking.
Although in its early stages, Mr Waterhouse said the expansion was all "the future of Hawke's Bay's youth".
It was believed five courts would meet demand from the rapid growth of indoor sporting codes.
However the development would not go ahead without commitment from such codes that they would use the additional space.
"We would know that we're not just building it for the sake of building it," he said.
"We've made it very clear we're not building until we get those commitments because we don't want to take the risk. We're building it for them, if they're not going to use it then why are we building it?".
At this stage, the trust which runs Pettigrew Green Arena - the Regional Indoor Sports and Events Centre (RISEC) Trust - were focused on raising the money for the project's first stage.
About $1 million had already been raised - including a $100,000 grant on Sunday - and they were hoping to secure another $1.5 million to $2.5 million through public fundraising.
They would also be requesting funding, potentially from central government, and the Napier City Council.
When the council put their $22.9 million multi-use sports facility to bed last month, it signalled its $500,000 business case could go toward a business case on the arena's expansion.
And, the council agreed the funding allocated for the facility - over $5 million - be reallocated through the Long Term Plan 2018-2028 for other projects that "support community well-being".
The council has said it was expected the RISEC Trust would put a proposal forward for some of this funding to be allocated through the 2018/28 LTP. However this would need to be considered against all other proposed capital projects not yet funded in the LTP.
Yesterday Napier Mayor Bill Dalton said he was sure the expansion would be the sort of thing the council would be interested in funding, but that this might require funding from other local authorities.
"Nobody knows more about the demand for court space than the Pettigrew Green Arena, and if they're saying it's the right thing to do I'm happy to agree with them."