Small Area Dwelling Stock Removals

Experimental estimates of the number of dwelling stock removals in Victoria by Statistical Area Level 2 (SA2)

Released
10/11/2021

Introduction

Dwelling stock statistics are currently only available from the Census of Population and Housing every five years. More frequent estimates of dwelling stock are valuable for economic and housing policy development and evaluation, and informing planning and service provision decisions. The Australian Bureau of Statistics is currently developing a methodology for the production of quarterly estimates of small area dwelling stock for release in 2022. 

The newly developed statistics will contain quarterly estimates of dwelling additions, removals, and stock based on the most recent Census of Population and Housing.

The purpose of this article is to present an experimental method for estimating stock removals. Dwelling stock removals have been estimated in Victoria from the September 2016 quarter to the June 2021 quarter by Statistical Area Level 2 (SA2). Victoria was selected as it had the highest number of demolition approvals for all the states and territories across this period. The data are comprised of:

  • realised demolitions (demolitions as they occur following an approval); and
  • unplanned stock losses (dwellings destroyed due to natural disasters) from the 2019-20 bushfire season.

Experimental estimates of small area additions to stock (dwelling completions) from the September 2016 quarter to the June 2021 quarter are available in Building Activity, Australia. These estimates of small area completions have been modelled using state level dwelling completions, which are produced from the Building Activity Survey.

If you have any feedback on these experimental data and the potential for producing ongoing quarterly estimates beyond 2022, please email construction@abs.gov.au.

Key statistics

  • There were 36,712 total dwelling stock removals across Victoria from the September 2016 quarter to the June 2021 quarter.
  • The majority of these (36,358) were dwelling demolitions, while 354 occurred as a result of bushfires in 2019-20.
  • 88% of stock removals occurred in Greater Melbourne, whilst 12% occurred in the Rest of Victoria.
  • The SA2s with the largest numbers of stock removals in Victoria were Heidelberg West, Bentleigh - McKinnon, and Brighton.

State results

The graph below depicts quarterly dwelling stock removals in Victoria.

Stock removals in Victoria peaked in the March 2020 quarter, and were lowest in the March 2021 quarter. The March 2020 quarter includes the stock loss attributed to the Black Summer bushfires in Victoria.

Small area results

The table below shows the top ten Victorian SA2s with the largest number of total stock removals between the September 2016 quarter and the June 2021 quarter. The number of dwelling completions is given alongside stock removals. Net additions are given by the subtraction of stock removals from completions. All of the SA2s with the highest numbers of total stock removals are in the Greater Melbourne area.
 

Areas with highest number of dwelling stock removals from September 2016 quarter to June 2021 quarter
Statistical Area Level 2 (SA2)Stock removalsCompletionsNet additions
Heidelberg West52415811057
Bentleigh - McKinnon44217801338
Brighton (Vic.)429830401
Balwyn North428822394
Bentleigh East (North)4031073670
Mount Waverley - South394798404
Ashwood - Chadstone3911251860
Pascoe Vale38914531064
Keilor East3871082695
Glen Waverley - West38615341148

The following table shows stock removals, completions and net additions between the September 2016 quarter and the June 2021 quarter for the Victorian SA2s impacted by the 2019-20 bushfire season. 

Areas impacted by the 2019-20 bushfires
Statistical Area Level 2 (SA2)Stock removalsCompletionsNet additions
Orbost226131-95
Bruthen - Omeo76282206
Towong70711

Methodology

Realised demolition approvals

Realised demolition approvals represent demolitions as they occur following an approval from a local council or other approving authority. They differ from demolition approvals as there is a lag between approval and actual demolition taking place, and because not all approvals go ahead. A dwelling demolition is defined as the complete and intentional dismantling of a dwelling, such that none of the structure remains on site. 

Estimates of realised demolitions have been calculated using a survival model based on the demolition outcomes of a sample of Victorian demolition approvals, which were investigated using aerial imagery. 
 

Data sources

Demolition approvals are sourced from Building Approvals, Australia. Demolition outcomes (i.e. whether the demolition occurred and the demolition date) for a sample of Victorian demolition approvals were ascertained using aerial imagery from Nearmap Australia Pty Ltd. The sample consisted of approximately 12% of demolition approvals (893 dwellings) within the 2017-18 financial year from across Victoria. This period was chosen to allow enough time following approval for the demolition to have occurred.

The date of the first image where visual evidence of a demolition could be identified was recorded as the demolition date. It should be noted that frequency of Nearmap image captures will affect the accuracy of the demolition date. Nearmap image updates are prioritised for major Australian metropolitan areas and occur more frequently than in regional areas. 
 

Method

For each approval in the sample, the time from approval to demolition was calculated in days. The average time between approval and demolition was 84 days in Greater Melbourne and 137 days in the Rest of Victoria.

The survival function for a dwelling surviving (i.e. not yet being demolished) was first estimated using a non-parametric (Kaplan-Meier) estimator. Based on this, the probability of a dwelling being demolished before 200 days after approval was estimated at 85%.

The survival model was next estimated using a parametric (log-normal) distribution as this was the best fit to the distribution of demolition outcomes based on the survival analysis. The survival model uses the parameters from this distribution to calculate the probability of a demolition occurring in a particular quarter. 

Adjustments were made to the survival model to account for the proportion of approvals where:

  • demolition did not occur;
  • demolition occurred prior to the approval date; or
  • demolition occurred in excess of two years after the approval date.

As the vast majority of demolitions occurred within six quarters (546 days) after approval, this was used as the cut-off point after which demolition approvals cease to contribute to realised demolition estimates. 

To derive the number of realised demolitions, the probability of a demolition occurring was calculated for each demolition approval six quarters prior to the reference period and summed by quarter.

The graph below depicts demolition approvals and realised demolitions for the period between the September 2016 quarter and the June 2021 quarter. Realised demolitions over time are lower than demolition approvals due to approvals which do not go ahead. 
 

Unplanned stock losses

Unplanned stock losses refer to dwellings that are unintentionally and permanently destroyed (i.e. they cannot be repaired/restored). This includes dwellings destroyed in natural disasters such as bushfires, floods and cyclones. Temporary removals from stock where dwellings may be uninhabitable for a period of time following a natural disaster are not currently in scope.

Counts of destroyed dwellings are not currently available in a nationally consistent and timely manner. Dwelling losses from major disaster events are incorporated into estimates of dwelling removals where data is available from relevant Government authorities. The availability and quality of this data may improve in future, as data consolidation around disaster management and resilience progresses.

Estimates of unplanned stock losses for the period from the September 2016 quarter to the June 2021 quarter have been compiled based on currently available data from relevant Government authorities, which cover the 2019-2020 bushfire season only. Unplanned stock losses that occurred in Victoria as a result of this event were allocated to the March 2020 quarter.

The ABS is continuing to investigate alternatives to estimate unplanned stock losses where direct counts are not available (i.e. based on the location of dwellings and hazard exposure information).
 

Data sources

Counts of dwellings destroyed by Local Government Area (LGA) and bushfire boundaries for the 2019-2020 bushfire season have been sourced from the National Recovery and Resilience Agency. Total dwelling counts by mesh block have been sourced from the Census of Population and Housing, 2016.

Method

The LGA counts of dwellings destroyed were allocated to SA2s based on the proportion of exposed dwellings in each mesh block within an LGA.

The number of exposed dwellings in each mesh block and LGA was calculated by multiplying the proportion of the area that was affected by bushfires (based on the bushfire boundaries) by the 2016 Census dwelling count. This was used to calculate the proportion of exposed dwellings in each mesh block within an LGA, which was multiplied by the number of destroyed dwellings in the LGA. The estimate of dwellings destroyed in each mesh block was then aggregated to the corresponding SA2.
 

Scope

ABS building statistics (building approvals, building activity and the dwelling stock series currently under development) classify buildings according to the Functional Classification of Buildings. This defines a dwelling as a self-contained suite of rooms intended for long-term residential use, including cooking and bathing facilities. Regardless of whether they are self-contained or not, rooms within buildings offering institutional care (e.g. hospitals) or temporary accommodation (e.g. motels, hostels and holiday apartments) are not defined as dwellings. This differs from the definition used by the Census (a structure which is intended to have people live in it, and which is habitable on Census night), which can include non-permanent structures such as caravans, houseboats and tents, as well as communal or transitory accommodation such as cabins, hotels, prisons and hospitals. 

Data downloads

Total stock removals in Victoria by SA2, September quarter 2016 to June quarter 2021