1367.5 - Western Australian Statistical Indicators, Dec 2001  
ARCHIVED ISSUE Released at 11:30 AM (CANBERRA TIME) 17/01/2002   
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Special Article - A View of Housing Density in Perth


INTRODUCTION

New housing developments are being influenced by a variety of housing types designed to cater for the diversity of housing needs within the community. These influences include a move to smaller lot sizes and to a range of multiple dwelling developments such as semi-detached housing, townhouses and grouped housing. One consequence of this trend has been an increase in housing density which is occurring to varying degrees (in part through urban infill) across the Perth metropolitan area.

There has been an increasing need for information on trends in medium density housing in Western Australia as government, industry and the community seek to better understand the impacts of higher density living on the provision of support services and on the community generally. While building approvals statistics published by the Australian Bureau of Statistics (ABS) provide a broad measure of medium density housing, the measure does not include grouped dwelling developments, i.e. developments in which two or more detached dwellings (houses) are constructed on a parcel of land.

This article presents findings from an ABS analysis of building approvals data covering the three financial years from 1998-99 to 2000-01 for the Perth metropolitan area. The focus for the analysis was to understand the extent of grouped dwelling developments; the trends in such developments over time; and their impact for expanding the view of medium density housing already available from building approvals statistics. The findings have the potential to better inform planning and assist in the provision of infrastructure required to support areas of increased housing and population density.


BACKGROUND

ABS publishes building approvals data according to building type categories defined in the ABS Functional Classification of Buildings (FCB - a more detailed description is provided below under the heading "Study Methodology and Definitions"). These statistics provide a broad indication of housing density, i.e. houses (low density); semi-detached, row or terrace houses, townhouses, etc. (medium density); and flats, units or apartments (high density). However, there has been an apparent trend toward an additional form of multiple dwelling development in the Perth metropolitan area which comprises two or more detached dwellings (houses) constructed on a parcel of land - commonly referred to by the housing industry as "grouped dwellings". These dwellings are currently classified and published as houses in accordance with the ABS FCB.

The analysis set out to identify multiple dwelling development approvals over the three years 1998-99 to 2000-01, particularly approvals for the construction of grouped dwellings. This analysis was undertaken in the knowledge that the original approvals data and the methods used to produce building approvals statistics were not specifically designed to measure trends in dwelling density. Hence, not all grouped dwelling developments were able to be identified e.g. an approval for a house to be built on a parcel of land which already contains an existing dwelling. Nevertheless, the findings presented below from the analysis of building approvals data form a reasonable surrogate measure of trends in grouped dwelling developments.


FINDINGS

The following analysis shows the number of grouped dwellings identified; examines the degree to which grouped dwellings expand current measures of housing density; and shows the geographic distribution of this expanded view of multiple dwelling developments.

The methodology developed to identify multiple dwelling developments as well as definitions for specific dwelling types referred to in the findings from this analysis are described below under the heading "Study Methodology and Definitions".


NUMBER OF DWELLINGS

The following table shows the number of dwelling units approved in building types defined by the FCB. The data are as published in August 2001.

RESIDENTIAL BUILDING APPROVALS, Perth Statistical Division

NUMBER OF DWELLINGS
Building type
1998-1999
1999-2000
2000-2001
Total
Houses(a)
12 105
13 253
8 709
34 067
Semi-detached, etc
1 720
1 824
1 329
4 873
Flats, units, apartments
732
1 722
1 314
3 768
(a) Includes houses approved in grouped dwelling developments.

Source: Building Approvals, Western Australia (Cat. no. 8731.5).


To compile an alternative broad measure of medium density housing, house approvals identified from the analysis as constituting grouped dwellings were combined with semi-detached-type dwelling approvals to derive the category "clustered dwellings". The figure below depicts this process and shows the number of clustered dwellings approved in each of the reference years as well as the contributions made to this category by grouped dwelling and semi-detached-type dwelling developments.

Image - Figure depicting the process of Residential Building Approvals - Perth Statistical Division



Of the 42,708 dwelling units approved from 1998-99 to 2000-01, 80% (or 34,067) were houses. Analysis of these house approvals established that:
  • 14% (or 4,823) were constructed as grouped dwelling developments, a proportion that has remained relatively unchanged over each of the three reference years; and
  • a further estimated 2% of house approvals appeared to be part of a clustered dwelling development (e.g. a house approval together with a semi-detached dwelling approval being constructed on the same parcel of land - see the diagram in the discussion of "Other Multiple Dwelling Developments" included under the heading "Study Methodology and Definitions" below). However there was insufficient information to identify such developments conclusively. Consequently these house approvals remain classified as Houses for the purpose of the analysis.

Clustered dwelling developments (grouped dwelling and semi-detached-type dwelling approvals) over the three study years totalled 9,696. Grouped dwellings comprised half of the clustered dwellings category, their number being slightly higher than semi-detached-type dwellings in two of the three years.

As a result of applying the methodology to new residential approvals over the three years:
  • a significant number of approved houses have been identified as grouped dwellings, resulting in the broad indicator of low density housing (i.e. single house approvals) being 68% of all dwelling units approved. This compares with 80% when the FCB building type "houses", which includes grouped dwellings, is used; and
  • the proportion of dwellings considered representative of a broad measure of medium density housing is 23% (comprising clustered dwellings) whereas, for semi-detached type dwellings only, the proportion was 11%.

Flats, units and apartments make up the remainder of approvals.


CLUSTERED DWELLINGS - DENSITY AND GROSS SITE AREA (GSA)

The ability to identify clustered dwelling approvals provides the opportunity to examine the number of dwellings associated with each approval (a broad measure of medium density housing) as well as variations in the average gross site area per dwelling in clustered dwelling developments.

As shown in the following table, the highest proportion of clustered dwellings comprised approvals of 5 or more dwelling units (41%) and 2 dwelling units (30%).

CLUSTERED DWELLINGS, Perth Statistical Division, 1998-99 to 2000-01
DWELLINGS
Dwelling units per approval
No.
% of total
2
2 930
30.2
3
1 587
16.4
4
1 124
11.6
5 or more
3 994
41.2
Other(a)
61
0.6
Total
9 696
100.0
(a) Unable to establish cluster category.


While the number of clustered dwellings provides a broad measure of medium density housing, a more informative view can be obtained by examining these developments in conjunction with their reported Gross Site Area or GSA (i.e. the site area or size of the block, in square metres, on which the approved building work is being carried out). The results are shown below.

There were known deficiencies in the quality of GSA data as supplied by local government authorities - GSA is a mandatory item which is not well reported by some councils. Nevertheless, these results serve as a general indication of variations in housing density within the clustered dwellings category.

CLUSTERED DWELLING APPROVALS, Average GSA per dwelling

2 CLUSTERED DWELLINGS
Graph - Clustered dwelling approvals, average GSA per dwelling - 2 clustered dwellings


3 CLUSTERED DWELLINGS

Graph - Clustered dwelling approvals, average GSA per dwelling - 3 clustered dwellings


4 CLUSTERED DWELLINGS

Graph - Clustered dwelling approvals, average GSA per dwelling - 4 clustered dwellings


5 OR MORE CLUSTERED DWELLINGS

Graph - Clustered dwelling approvals, average GSA per dwelling - 5 or more clustered dwellings



The average GSA per dwelling decreased as the number of dwellings within each clustered dwelling development type increased. The largest proportion of dwellings for various development types fell in the following average GSA per dwelling range:
  • 2 dwelling developments: 31% in the range 400-499 square metres;
  • 3 dwelling developments: 50% in the range 300-399 square metres;
  • 4 dwelling developments: 45% in the range 200-299 square metres;
  • 5 or more dwelling developments: 38% in the range 200-299 square metres.

By comparison, the largest proportion of single house approvals (31%) had an average GSA in the range 600 to 699 square metres as depicted in the figure below.

SINGLE HOUSE APPROVALS, Average GSA Per Dwelling
Graph - SINGLE HOUSE APPROVALS, Average GSA Per Dwelling



CLUSTERED DWELLINGS - GEOGRAPHICAL DISTRIBUTION

The degree to which clustered dwelling developments are occurring across the Perth metropolitan area is depicted in the following map.

In 22% of Perth suburbs, clustered dwelling approvals comprised 48% or more of total dwellings approved over the reference period. In another 25% of suburbs, the proportion ranged between 21% and 48%.

There were four notable suburb groups within which clustered dwellings comprised 48% or more of new dwelling approvals:
  • North Coastal - including the suburbs of Scarborough and Innaloo;
  • North Central - including the suburbs of Tuart Hill and Joondanna;
  • Perth South - including the suburbs of South Perth and Como; and
  • Fremantle South - including the suburbs of Hilton and Hamilton Hill.

All are established residential areas, suggesting that there is an increase in urban infill occurring across the Perth metropolitan area.

CLUSTERED DWELLING APPROVALS AS A PROPORTION OF TOTAL DWELLING APPROVALS

Image - Map - CLUSTERED DWELLING APPROVALS AS A PROPORTION OF TOTAL DWELLING APPROVALS

STUDY METHODOLOGY AND DEFINITIONS

Functional Classification of Buildings - Residential Component

The FCB is used by ABS to code buildings according to the intended main purpose of the building. For residential buildings, the codes and their descriptions are:


FUNCTIONAL CLASSIFICATION OF BUILDINGS, Residential component

CodeDescription
Houses
011 Separate house
012Kit house
019Transportable house (excluding caravans and mobile homes)
Semi-detached, row or terrace house, townhouse, duplex, etc.
021One storey
022Two or more storeys
Flat, unit or apartment in a building of:
023One or two storeys
024Three storeys
025Four or more storeys
026Flat, unit or apartment attached to a house

From 1 July 2001, the ABS commenced coding building approvals using a revised FCB. The residential sector of the classification has remained unchanged. More details are provided in the August issue of Building Approvals, Australia (Cat. no. 8731.0).

Identifying Multiple Dwelling Developments

Grouped dwellings

Building approvals classified to a house (i.e. FCB code in the range 011 to 019) and consisting of 2 or more dwelling units (reported Number of Dwellings greater than 1) were separately identified as grouped dwellings.

Other multiple dwelling developments

Other types of multiple dwelling developments appeared to be represented in the approvals data but could not be conclusively identified. Examples include:
  • a house and a semi-detached-type dwelling to be constructed on a single parcel of land, as depicted in the following diagram. These developments appear as separate approvals in ABS data and could not be matched due to insufficient information; and
  • an approval for a dwelling(s) to be constructed on a parcel of land on which a house already exists, in which case only the new dwelling approval(s) have been considered within definitions used in the study.

Image showing 3 dwellings: 2 attached and 1 detached
General Description - 3 dwellings: 2 attached and 1 detached

ABS FCB - 1 house: 2 semi-detached-type dwellings

Study description - 2 approvals: 1 house and 2 clustered dwellings


Definitions of Building Categories Devised for this Study

The following building type categories devised for this study are based on concepts or terms generally accepted in the Western Australian user community.

Single House

A detached building primarily used for long term residential purposes and consisting of one dwelling unit on a single parcel of land. This is essentially the ABS definition of a house (FCB codes 011 to 019) qualified to indicate the approval/construction of only one house on a parcel of land.

Grouped dwelling

Formed when two or more detached dwellings (houses) are grouped together as a single approval and constructed on a single parcel of land (as depicted in the figure below). These development types are an increasingly popular alternative method of construction to duplex- and triplex-type housing (FCB codes 021 and 022). Survey strata schemes are often used with these developments as an alternative means of lot subdivision to provide for an exclusive area to be occupied by, and used by, each dwelling. This analysis was able to identify such developments which correspond with the WA housing industry's description of grouped dwellings.
Image - 3 detached dwellings
General Description - 3 detached dwellings

ABS FCB - 3 houses

Study description - 3 clustered/grouped dwellings

Clustered dwellings

Comprise grouped dwelling developments (as defined above) and semi-detached-type developments (FCB codes 021 and 022). This category represents a broad indication of medium density dwelling development. It is an extension of the currently available indicator represented by semi-detached-type developments. The figure included under the heading "Number of Dwellings" above depicts the process of deriving clustered dwelling developments.


CONCLUSION

The above analysis has expanded the range of ABS measures of housing density. Building approvals data have been used to identify and reclassify grouped dwellings from low to medium density.

For clustered dwellings, the results illustrate the trend toward a smaller average gross site area per dwelling as the number of dwellings in such developments increases. The results also point to an increase in urban infill occurring across the Perth metropolitan area, particularly in the more established residential suburbs.


ADDITIONAL INFORMATION

For further information on this analysis, please contact Robin Dalby on Perth (08) 9360 5254 or email: robin.dalby@abs.gov.au. For general information on Building Approvals, including requests for data, please contact Andrea Woods on Adelaide (08) 8237 7350.

REFERENCES

Building Approvals, Western Australia (ABS Cat. no. 8731.5)

Building Approvals, Australia (ABS Cat. no. 8731.0)

Australian Standard Geographical Classification (ASGC) (ABS Cat. no. 1216.0)

ABS Functional Classification of Buildings