●A Case of Utilizing Results
Analysis of Levels of Rebuilding in Relation to Urban
Characteristics, and Incorporation in a Revision of the Policy forImproving Densely Built-Up Areas in the Basic Plan for Housing(National Plan)
KATSUMATA Wataru (Dr.Eng.), Senior Research Officer, Urban Development Division, Urban
Planning Department
KIUCHI Nozomu (Dr.Eng.), Head of Urban Disaster Mitigation Division, Urban Planning
Department
TAKEYA Shuichi (Dr.Eng.), Head of Construction Economics Division, Research Center for Landand Construction Management(Keywords)

Densely built-up areas, rebuilding rate, urban characteristics, database, Basic Plan for Housing

1. Introduction
Dangerous and densely built-up areas mainly
consisting of old wooden houses where large-scale urban
fires could break out in the event of an earthquake still
exist over a wide area of Japan; these areas need to be
redeveloped with greater urgency in order to improvetheir disaster prevention performance. However, theurban characteristics affecting rebuilding of densely
built-up areas are diverse, and levels of rebuilding
leading to improved disaster prevention performance andeffective measures of redevelopment are expected todiffer from district to district. It is therefore important toascertain the rebuilding rate in relation to the physical,
social and economic properties of a district. These will
include the state of road foundations and scale of land lots,
population structure including declining birth rate, aging
and population decline, and economic potential.
However, the rebuilding rate in each densely built-up
areas has not become clear, owing to the difficulty ofobtaining data. As a result, it has been impossible tocompare the rebuilding rate in different types of urban
area, or to quantitatively analyze the relationship with a
district’s physical, social and economic properties, which
may be considered contributing factors in terms ofrebuilding.
2. Construction and analysis of a macro database on
urban characteristics of priority densely built-up
areas throughout JapanNILIM has therefore constructed a macro database
after gathering data on individual districts in a total of 400“priority densely built-up areas” nationwide (meaning“densely built-up areas where large-scale fires could
break out in the event of an earthquake, etc., and wherepriority improvement is required” as announced by MLIT
on July 11th, 2003). The data collected include physicalindicators (building stock classified by construction year,
small lot ratio, narrow street ratio, etc.), socio-economicindicators (population change, aged ratio, population by
5-year age groups, 5-year settled domicile ratio, land
prices and trends in the same, etc.), and policy or projectprioritization. With regard to the rebuilding rate, data on“newbuild renewal ratio” were calculated by dividing thenewbuild floorspace area in recent years by stock, using
data on the property tax ledger. This enabled us toascertain the state of rebuilding for each district, compare
this by type of urban area, and quantitatively analyze thecorrelation between the rebuilding ratio and otherphysical, social and economic indicators.
The analysis results quantitatively confirmed that thenewbuild renewal ratio differs according to the type ofurban area (Fig. 1), and that a district’s newbuild renewal
ratio is influenced, among others, by urban characteristics
such as the aged ratio, small lot ratio, narrow street ratio(Fig. 2), distance from the nearest station, rented landratio, and designated floor-area ratio. These havepreviously been pointed out empirically and qualitatively
as factors hindering rebuilding.
3. Incorporation in a revision of the Basic Plan forHousing (National Plan)
In March 2011 the Basic Plan for Housing (NationalPlan) that defines the government’s policy on improving
densely built-up areas was revised. As a new target forimprovement, it was indicated that approximately
6,000ha of densely built-up areas that would be markedly
dangerous in the event an earthquake, etc., would be
mostly eliminated in 10 years. As for basic measures
aimed at achieving the improvement target, meanwhile,
the Ministry conducted a study to find which measureswould be effective to suit the type of urban area and urban
characteristics. This was based on the results of research

●A Case of Utilizing Results
by NILIM on the state of rebuilding in priority densely
built-up areas, seen in terms of different types of urban
areas and urban characteristics such as the narrow street
ratio. As a result, in addition to conventional measuresinvolving the rebuilding or removal of dilapidated
buildings posing a high risk of fire spread or collapse, theneed for finely detailed measures in relation to local
characteristics were incorporated into the Plan as basic
measures aimed at achieving improvement targets. These
include evacuation routes and firefighting environments
in historical urban areas and other similar districts whererebuilding cannot be expected. They also include the useof relaxed restrictions related to road width based on the
Building Standard Law, to encourage rebuilding indistricts where the narrow street ratio is high (roadfrontage conditions are bad).

100%
90%
80%

11.0%

21.9%

6.7%

24.4%

7.1%

6.7%
5.0%

0.0%

0.0%

70%

40%

0.0%
7.7%

30%
10%

100.0%

51.7%

20%

50%
40%

10%
0%

1-2%
69.2%

Less
than 1%

47.8%

23.2%

Miners’housingarea, etc.

FishingvillageSloping landMainthoroughfare

Historica
urban area

Postwarsprawl area

Urban
sprawl area

3% ormore
2-3%

40.8%
47.6%
40.0%

76.9%
42.9%

22.5%

1-2%
Less
than 1%

23.8%

Less 25-50% 50-75% 75% orthanmore
25% Narrow street* ratio(* under 4 meters wide)

0%
Centralurban area

15.4%

23.8%
30.0%

20%

35.6%
20.5%

0.0%
7.7%

30%

3% or
more
2-3%

46.6%
75.0%

4.1%
12.2%

60%

23.1%

60%
51.8%

4.8%

Fig. 2 Newbuild renewal ratio by narrow street ratio in
connection with priority densely built-up areas
nationwide (based on total floorspace area)

34.8%
33.3%

7.5%

70%

17.9%
36.7%

50%

90%
80%

0.0%
7.1%

17.4%

17.9%

100%

Fig. 1 Newbuild renewal ratio by type of urban area inconnection with priority densely built-up areas
nationwide (based on total floorspace area)- 2 -