A new free residential property database will soon be expanded and more information added.

Jeremy O'Hanlon of homes.co.nz said the details of 1.2 million New Zealand residences, flats and apartments were now accessible, giving up-to-date valuations on each residence and its site.

"These are all things you've had to pay for in the past," O'Hanlon said, explaining how the information was drawn from authorities including councils, which hold property records. "We've got the sales history, estimated value and we're now working with Westpac and IAG to add new data sets."

The site's computer model uses the data, historic sales and trends in each area, which is updated monthly, to give people an idea of an estimated value. Property sales history, recent sales, monthly homes estimate and rating values are on the site.

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Real estate agents - who have profiles on the site - and industry partners made the business model work financially, said O'Hanlon.

John Holt, a director of homes.co.nz and its chief executive, said much more information would soon be available.

He is one of the founders of the business, which has its headquarters in Auckland, and a director of PropertyNZ, trading as homes.co.nz.

Originally from Canterbury, with an IT background, he said the new data would include details on electricity use in each house, information on warranties and guarantees, and even how much sun a roof gets, enabling owners to gauge the benefits of installing solar panels.