This section has information about data that does not change between releases.
Data for building consents is obtained each month from all accredited building consent authorities (ie territorial authorities). Statistics New Zealand compiles information from all building consents issued each month, provided they are valued at $5,000 or more, and are not predominantly for demolition work.
Because the survey has 100 percent coverage of the target population, there is no sample error.
These errors can occur when there is incomplete or incorrect information on consent forms, or when information is incorrectly delivered, interpreted, or classified. While much effort is made to minimise these errors, they will still occur, and it is not possible to quantify their effect.
Only construction work that requires a building consent is included. Some civil engineering works, such as roads, require resource consents but not building consents, so are excluded.
The scope of work requiring a building consent is determined by the Building Act 2004. Its main parts came into force in 2005, replacing the Building Act 2001. The new act introduced measures to provide greater assurances to consumers, such as registration of building consent authorities, and the licensing of building practitioners. The act was reviewed in 2009, and broadened the scope of work that may proceed without a building consent (for example, see changes to Schedule 1 of the Building Act 2004, on the Department of Building and Housing's website, effective from 23 December 2010).
The Canterbury Earthquake Recovery Authority has legislative powers to undertake work without a building consent, for example, demolition work and temporary repairs.
Statistics NZ excludes consents that are predominantly for demolition work, and consents valued below $5,000.
Changes in coverage
The building consents included in this release have changed over time, and the list below highlights the key changes.
1996 From the June 1996 month, consent values for multi-purpose buildings are coded to one or more of the most appropriate building types. Before this date, multi-purpose buildings were classified separately.
1993 From the January 1993 month, building authorisations have been applied for under the building consents system administered by territorial authorities. Before this date, applications were made under the building permits system. The building consents system has wider coverage than the building permits system. The additional coverage includes some government building (particularly work on education buildings), and on-site drainage and reticulation work.
1989 From the September 1989 month, consents below $5,000 are excluded.
2011 From 1 November 2010, part of the former Franklin district moved from the Auckland region to the Waikato region. This change is included in Building Consents data from January 2011.
2010 On 1 November 2010, the new Auckland Council came into being (see table 4). Before November 2010, the Auckland region (see table 3) can be used to approximate the new Auckland Council.
Seasonally adjusted series
Seasonal adjustment removes the estimated impact of regular seasonal events, such as summer holidays and pre-Christmas purchasing, from statistical series. This makes figures for adjacent periods more comparable.
The seasonally adjusted series are re-estimated monthly when each new month’s data becomes available. Figures are therefore subject to revision, with the largest changes normally occurring in the latest months.
The X-12-ARIMA seasonal adjustment program, developed at the U.S. Census Bureau, is used to produce the seasonally adjusted and trend estimates.
Trend estimation removes the estimated impact of regular seasonal events and irregular short-term variation from statistical series. This reveals turning points and the underlying direction of movement over time.
The trend series are re-estimated monthly when each new month’s data becomes available. Figures are therefore subject to revision, with the largest changes normally occurring in the latest months. Revisions can be large if values are initially treated as outliers but are later found to be part of the underlying trend.
The X-12-ARIMA seasonal adjustment program is used to produce the seasonally adjusted and trend estimates. Irregular short-term variation is removed by smoothing the seasonally adjusted series using optimal weighted moving averages.
To reduce distortions, the monthly trend series for the value of non-residential buildings is estimated after removal of consent values of $25 million or more between January 1990 and December 2005, and of $50 million or more from January 2006. However, non-residential building consent values are still volatile with no stable seasonal pattern, and therefore a stable trend for this series is slow to emerge.
Further information on seasonal adjustment is available on the Statistics NZ website.
Interpreting the data
Figures for new apartments are compiled from consents that have 10 or more new attached dwelling units (flats or apartments). If there are fewer than 10 flats or apartments on a consent, they are treated as being dwellings other than apartments. Apartment numbers often show large fluctuations from month to month and, unless removed from dwelling figures, can mask underlying movements.
Values for new buildings include conversion costs. For example, if a hotel is converted to apartments, these are treated as new dwellings in the statistics. Consent values for new buildings sometimes include the cost of demolishing or removing the previous buildings.
Some consents, particularly for large projects, are issued in stages across more than one month. Value data is collected at each stage but floor areas and dwelling or building counts are normally recorded at the first large stage of the project. This difference in timing can affect calculations of average prices.
Trading day adjustments
An aim of time series analysis is to identify movements that are due to actual changes. Seasonal adjustment is done to remove systematic calendar-related variation. Specific adjustments can be made to remove variations due to trading day differences and moving holidays, such as Easter, which are not accounted for in a standard seasonal adjustment.
Some of the apparent movement in building consent figures is due to trading day differences between months. For example, a month with four weekends will have more trading or working days than a comparable month with five weekends. This can affect monthly figures, even though there may be no difference in the length of the month or difference in the rate at which consents are issued. Trading day effects, when estimated to be statistically significant, are quantified and removed. This is trading day adjustment.
Since 1998, trading day adjustments have been made to the building consents series during the seasonal adjustment process. Since May 2004, an improved method has been used. At present, there is no adjustment to remove the effect of moving holidays such as Easter.
Trend estimates versus month-on-month comparisons
Trend estimates reveal the underlying direction of movement in statistical series. In contrast, comparisons of unadjusted data between one month and the same month in the previous year/s do not take account of data recorded for the intervening months, and are subject to one-off fluctuations. Reasons for fluctuations include changes in legislation, economic variables such as interest rates, and trading day composition of months.
More information about Building Consents Issued is available on our website
While all care and diligence has been used in processing, analysing, and extracting data and information in this publication, Statistics NZ gives no warranty it is error-free and will not be liable for any loss or damage suffered by the use directly, or indirectly, of the information in this publication.
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