Seasonally adjusted consents were down 6.3 per cent in February.

Home building plans are disappointing for the third month in a row, despite a record migration boom adding to housing demand.

Housing consents took a hard knock in February, falling more than 6 per cent in the month after a near 5 per cent drop in January.

Economists said Auckland especially was not building enough homes for its growing population, rocket-fuelled by a record migration boom.

With a continued housing shortage and low interest rates, house prices in Auckland were expected to keep on rising, after gaining 14 per cent in the past year.

Statistics NZ figures showed a total of 1758 new dwellings were consented around the country in February. Apartment consents were high late last year and have fallen from those recent peaks.

Overall, consent numbers are barely higher than in February last year and the post-election rebound in building plans has lost steam.

Seasonally adjusted consents were down 6.3 per cent in February and if the soft figures continued it could mean construction growth has stalled because there are not enough workers, or possibly because house building costs were rising too fast, economists said.

ANZ Bank economists said higher construction costs may be starting to bite on consent numbers. ANZ estimated housing construction costs rose close to 10 per cent in the past year, the strongest rate since 2008.

But the weakness in consents would be a concern for the Reserve Bank which hoped to see a strong lift in house building to offset a growing population and ease its worries about racing house prices and bank stability.

In sharp contrast, commercial building work remains strong. Non-residential building consents in February were worth $469m, up 25 per cent on a year before. There were growing numbers of industrial and storage buildings, and offices.

Deutsche Bank said building work would support economic growth. Work was still needed to earthquake-strengthen buildings, repair leaky homes and meet pent up demand for homes and commercial buildings in Auckland.

But ASB Bank economists said the soft dwelling consent figures were "particularly concerning" and hard to explain.

There may have been some disruption to building demand from the summer holiday period. Or it may be that building numbers were moving sideways because the construction sector is already close to flat out.

In the past year, almost 25,000 homes and apartments have been built, after picking up dramatically from the housing trough four years ago when 10,000 fewer homes a year were built.

Home building consents were now running at a slower pace than in the first half of last year, suggesting the trend in the pipeline was falling, not rising.

That was in contrast to expectations that home building would keep rising, led by Auckland and Canterbury.

Auckland's annual housing consents are still running at about 7700, seen as well short of what the city needs to build to cope with a housing shortage, of at least 10,000 a year.

Deutsche Bank said the recent run rate for Auckland consents was "well below" what they estimated the city needed to meet demand due to "very strong population growth".

Auckland house prices have shot up about 14 per cent in the past year, while house price inflation in the rest of the country is up just 3 per cent.

A critical reason for rapidly rising house prices in Auckland is the current migration boom, running at more than 50,000 net gain in the past year.

The bulk of those new arrivals stay in Auckland adding pressure to the housing market. A Wellington source said the migration boom was a "huge" factor in the Auckland housing market.

The growth in the number of migrants alone suggests demand for about 8000 new homes a year in Auckland, but annual consents are running at only about 7700 a year.

Some estimates suggest the region needs at least 10,000 new homes a year for a long period to start catching up with demand.

Given rising house prices in Auckland, the Reserve Bank was expected to keep in place speed limits on low deposit home loans for the rest of the year, ASB said.

But new house building is now exempt from high LVR limits so was not a road-block to more homes being built.

The other key house building market is in Canterbury, with 517 consents in February, which was down slightly on the same month a year ago, despite the massive earthquake rebuild. Wellington sources said there may well be an oversupply of homes in Canterbury in time as properties are repaired and new homes completed.

Westpac senior economist Michael Gordon said the finite nature of the post-quake rebuild meant the level of building work would eventually "peak and decline" but there was no sign that point had been reached yet.

Home numbers:

Total consents down 6.3 per cent from January, seasonally adjusted.

But the trend for consents has more than doubled since the bust in house building in 2011.

February dwelling consents;

Total: 1758

Homes: 1598

Apartments and retirement units: 160

By region:

The hot:

Auckland: 528 consents, up from 464 last February

Canterbury: 517 consents, down from 530 last February

Medium:

Wellington 102 consents, down from 114 last February

The cold:

Taranaki consents: down 21 to 25

Otago: down 18 to 73

Bay of Plenty: down 13, to 101

Source: Statistics NZ