• Inside Story: The Big Squeeze
The council's proposed changes would enable, for instance, four units to be built on an 800sq m property instead of two, making it viable for developers to buy and demolish existing houses and rebuild intensively.
Mr Thompson says this could be a gamechanger, making terraced housing and small family homes worthwhile for developers in mid-value suburbs such as Glenfield, Glendene, New Lynn, Mt Wellington and Otahuhu - places with larger section sizes which could be subdivided into 200sq m lots.
Elsewhere, higher land values would continue to result in plush, expensive houses being built, which only a minority can afford.
Mr Thompson estimates 75,000 additional homes could be built in the two mixed housing zones - just how many would largely depend on the number of willing sellers and continued demand.
"This will be the most dramatic change seen in the city's housing market for more than 20 years and will potentially mean a lot of houses will be built for less than $400,000 once the new plan is operative."
Major property developers welcome the planned changes - but are pressing for more tweaks to the notified plan to ease the path for high-rise apartments in high-value seaside suburbs such as Browns Bay, Milford and the isthmus eastern bays.
Any moves to increase density of development are likely to meet some resistance from homeowners worried about the effect of squeezing more units into traditional house and garden suburbs.
More worrying for homeowners in "character" neighbourhoods is a signal from the Unitary Plan hearings panel that the council should rethink rules designed to protect pre-1944 houses and commercial buildings from automatic demolition.
But Deborah Dunsford, co-chair of the Milford Residents Association, says increased densities raise few issues as long as height limits and design controls are in place - and rigidly enforced.
"If the rules are to be relaxed in our opinion there have to be firm controls in place about bulk and location, height-in-relation-to-boundary, etc," she says. "On large sites, if development is well-placed and isn't going to overpower the neighbours, we don't have a problem with it.
"Increased density allows more variety of housing - as long as it doesn't [completely] change the neighbourhood that's fine. But we can't have this creeping escalation of height and multiple dispensations."
Property Council chief executive Connal Townsend says the changes reflect a more scientific approach to gauging whether the Unitary Plan can cater for population growth.
They follow a study - ordered by the Unitary Plan hearings panel - which found many areas earmarked for apartments and terraced housing in the Unitary Plan were not yet economic to build on.
The Unitary Plan's residential provisions go before the plan hearings panel in October and land zonings are due for debate in February.
The plan is expected to become operative from July next year.
