Proposal of Effective Quality Control
andInsurance System of Construction Industry
Yuta KAWARASAKI, Seigo NASU
Kochi University of Technology
ABSTRACT: In this research, the kinds and the number of defective qualities are examined, and thecurrent state of the defective quality is understood. In addition, a social cost led by analyzing the quality
control cost function and the quality insurance cost function in making optimal balance, and requesting a
total cost are analyzed. The insurance system that adds the parameter of citizen’s senses of trust at the end
leading to an ideal social cost in evaluating the optimal construction management level is introduced.
KEYWORDS: management of effective quality control, construction of insurance systemessential to develop appropriate quality control

1. INTRODUCTION(inspection of construction process) system for
The quality issue in the construction industry ofminimizing the defects in a project.

Japan becomes a big problem with the regards of the

In the idea of the quality control system, it isdesign and execution management. The problem ofnecessary to read the quality control from the aspect

construction defect with large social influence levelof the entire construction industry in an individual

has decreased people’s reliance, and has come tobuilding. The optimal quality control level or

influence the house purchase.

construction management system is found from the

The system of the quality control of the design andeconomy in which both sides of the quality control

construction greatly lays a background for the issue

cost and the defective quality repair cost are

mentioned

construction

considered in an individual building. At the same

management system and industrial system that relies

time, it is required to correspond to the defective

on mutual trust does not always succeed.

quality that has occurred because it constructs theMoreover, a major factor to decrease the quality isinsurance system that secures the processing cost to

reduction in number of engineers at the construction

the defective quality from the aspect of constructingsite as well as engineers in the administration thatindustry-wide.

above.

It

comes

in

civil servant reduction rate fixed regardless of theinfluences of the system.
It is thought that it is necessary to review the ideal

2. QUALITY CONTROL IN INDIVIDUAL

way of the quality control again. On the other hand,

BUILDING

the defective quality (construction defect) is aproblem existing for a long time, and it is almost

2.1 Basic Policy

impossible to eliminate the defect completely. Since

In the quality control in an individual building,

it is not possible to imagine a defect free project, it isgrasping of problem in quality control in relation to1

the management is required. Then, the classification

Consequently, the number of defective quality isof the problems and their inter-relations are needed

40,000 during a year. And, about 400,000 houses areto be clarified.

being built in a year.

The feature and the rule of the defective quality

The defective housing rate is a probability of(quality of design, construction quality, equipment

approximately 10%.

quality, and material quality) are evaluated. Next, thedefective quality is systematized according to the2.2.2 Systematization of defective quality

stage. This is assumed to be a cause and effect

The defective quality is classified into the quality ofdiagram.

design, the construction quality, the equipment

And, it is divided into the various classification andquality, and the material quality by grasping thethe items. The total cost needed for the processing

defective quality (construction) obtained in theafter the number of defective qualities is examined

above-mentioned. And, the cause and effect diagramand is shown as a Pareto chart.

is made by specifying and systematizing a concrete

The structure of the quality control level is designed

item. In this text, it is very important to derive thefrom the amount of loss by the cause of the defective

factor of the defective quality and the result from it.

quality. And, the quality control level and the content

Systematization classifies the defective quality into

are decided. Then, the priority level of management

four (the design, construction, and equipment andat the construction stage to achieve a fixed defective

the material) as shown in Figure-1, and marks down

quality rate is decided.

the defective quality item at each stage. In Figure-1,

The data that relates to an actual inspection of

the stage of the design, construction, equipment, andconstruction process is needed in this process.

the material is divided into the factor of 22 all
together.

2.2 Methodology
2.2.1

Investigation

of

rate

of

defective

construction
The content and the factor of the defective quality by
the data of quality related to construction like faulty
workmanship and improper work are specified.
The relation between the content of the inspection of
construction process and the quality of the result isanalyzed.
At the beginning, the analysis of the quality control
problems based on the defective consultation annual

Figure-1: Systematization of defective quality

report was done. About 20,000 (For five years)
factors were presumed.

2.2.3

Moreover, because only the consultation annual

defective construction

report doesn't necessarily clearly show the number of

A Pareto chart consisting is the defective quality

actual defective qualities, interview was executed.

along transverse axis and, repair cost in the vertical

Number of defective housing is possibly ten times asaxis is shown in figure 2.

much as counted by an interview.

The repair cost of each defective factor is calculated
2

Renovation

cost

upon

occurrenceoffor all potential defective housing.

3.1 Basic Policy

The repair cost

(Price of material, cost of labor,

The quality control in the construction industry ismachine apparatus expense, hypothesis material

thought that the design of the most efficient quality

expense, haulage costs, and market unit price, etc.)

control system minimizing the total of both theof each defect trouble is quantified. It was classified

quality control cost and the quality security costaccording to the factor of the defective quality.

becomes possible. In a word, the optimal point at the

In Figure-2, the repair cost of each item according toquality control level is derived by selecting a

the factor is shown. Moreover, it is concrete thatminimum point of a total cost or a social cost. The

repair cost of the defective quality regarding a rebar,

construction

concrete, concrete form; a plasterer is high.

corresponding to the defective quality item ofThus, it confirms the importance degree of which

Figure-2 corresponding to the optimal cost can berequires high quality control. And, basic information

set.

management

level

at

the

level

can be arranged.
Methodology（Billion yen）

3.2.1 Quality control (Inspect of process) cost and

\14
\12

quality insurance (Accumulated repair) cost

\10

The optimization of the quality control system and\8\6

the insurance system is obtained by deriving the\4quality control cost function and the quality

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insurance cost function. The quality control costfunction is obtained by making a function to the cost

（Cause）

Air-

needed according to the construction managementlevel when the defective quality is prevented throughFigure-2: Total renovation cost of each defectthe inspection of construction process.
2.3 Quality control in individual building

On the other hand, it thinks the quality insurance

The quality control item according to the item

cost is calculated in the form of insurance. In a word,classification and the necessity of the importancethe quality insurance cost function is derived

degree can be confirmed in an individual processaccording to the cost needed to process the defective(quality of design, construction quality, equipment

quality.

quality, and material quality) from the above

corresponding to the defective quality rate.

discussion.

And, it is possible to tie to the

The amount of money that requires to makeestablishment of the construction management

amendments by calculating a defective rate at which

system for the improvement of the major items of

all buildings of targeting and each construction

the repair cost and to decrease the generation of the

management level of insurance in Japan that cannot

defective quality.

be evaded can be calculated by using Figure-2, andIt

isassumedthat

insurance(rate)

the quality insurance cost function is derived.
3. QUALITYCONTROLIN

THE

3.2.2 Deriving of quality (repair) insurance cost
The quality insurance cost can be derived by

CONSTRUCTION INDUSTRY

requesting the accumulation cost from the one whose3repair cost

Quality

is lower than the Pareto chart(construction)

controlcost

becomes(Figure-2).

725,000 yen (Inspection cost per total construction

The total of the repair cost of all the defective

cost, 3.6%) per household when all quality controls

qualities becomes 86.6 billion yen.

are executed, and quality (construction) control cost
during year becomes 290 billion yen. (Figure-5)( B i l l i on y en)

\100
\90
\80
\70
\60
\50
\40
\30
\20
\10
\0

Quality (repair) insurance cost

( B i l l i on y en)

\350
\300

\200

de
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ct
eq Me
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ic

\50

fr
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Ai

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( F a ctor)

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Figure-3: Quality (repair) insurance cost

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Ai

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\100

( F a ctor)

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Quality (construction) control cost

\250

Figure-5: Quality (construction) control cost

3.2.3 Derivation of quality (construction) control
cost
The quality control cost (Inspection cost of

3.2.4 Derivation of social cost

construction process) is calculated for the house

The total cost function that can be calculated by the(Architectural expense: about 20 million yen) of thesum total of the quality control cost (cost to makeRC structure.

amendments for defective quality) and the quality

A typical work schedule is made from theinsurance cost (construction management level

construction chart below. The inspection cost iscorresponding to defective rate) is obtained from thecalculated from a necessary number of engineers. In

quality control cost function and the quality

this case, third party inspector is expected to cost

insurance cost function.

20,000 yen per day.

This is a social cost that requires it to secure thequality of the building under consideration. It isthought that minimization point would offer mosteconomical & reasonable quality control system. It
becomes basic of a social system design to which thesum total of insurance in the insurance system basedon a defective rate corresponding to the quality
control cost corresponding to the construction
management level and is minimized. (Figure-6)

Figure-4: Management arrangement in typical work
schedule
Next, the required maintenance fee of each factor
of Figure-1(labor cost) was distributed, and the total
amount of money of the factor was derived.
4

the optimal point of a social cost moves in the
direction where a defective rate lowers.
In the design of the insurance system, when we set
insurance corresponding to the construction scale,when the premium rate is made constant by levelingregardless of the construction scale, it is necessary to
examine which is a good social system.

Figure-6: Social cost structure for quality securing
And it is preferable to minimize a social cost.
Minimizing a social cost from Figure-7 becomes thepart of the rebar. At this time, rock riprap and earth
work defects are controlled by the inspection of
construction process.

Figure-8: Changing of optimal point of social cost

And cover everything from the rebar to the metal as

according to construction scale

insurance. It becomes the optimal social system inthis case as a construction management level.

3.2.6 Citizen’s senses of trust
It is thought that citizen’s senses of trust to theconstruction industry are socially the critical factors,( B i l l i on y en)\350
Quality (construction) control cost
Quality (repair) insurance costSocial cost

\300
\250

and is necessary to consider it in designing quality(construction) management system and insurance

\200
\150

system.

\100

Citizen’s senses of trust quantitatively grasp people's

\50
\0

ic

to make trust to the function to compare it at thent( F a ctor)

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rt b aRo h w r
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Figure-7: Social costpoint of a total cost including citizen’s senses of trust
3.2.5 Relation between construction scale andcan be derived by subtracting it from a social cost.

social cost optimal point

A social cost is a negative factor, and citizen’s senses

It is thought that the relation between the qualityof trust become possible by deriving the optimal

control cost and the quality insurance cost changes

point by pulling the latter from the former because it

by the difference of the investment scale of theis a positive factor. (Figure-9)

building, and the movement of optimal point of a

A social cost is in increasing direction though itsocial cost.

becomes important to be as small as possible, a

The quality control cost to the construction expense

defective rate from people's aspects. It is important

lowers relatively when a construction scale ups. And

to set the tolerable quantity related to the increase of5

a social cost by considering citizen’s senses of trust.

by showing this by 400,000 households' isaccumulating in a year.
3.2.7 Social cost including citizen’s senses of trust
The preferable construction management level
finally requested has the necessity including
convenience of not a simple, social cost but citizen’s
senses of trust. Therefore, it leads to the decision of
the optimal construction management level by whichcitizen’s senses of trust are considered by adding to asocial cost in which the sense of trust of the

Figure-9: Relation between citizen’s senses of trust

requested people is previously derived. Citizen’s

and social costsenses of trust are added, and then, social costdecreases greatly from the reinforced concrete, and

It is necessary to request the amount of money fromconsequently

social

cost,

and

the

optimalthe quantification of citizen’s senses of trust that

construction management level is minimized in thegenerates corresponding to the level of the defectplasterer part as shown in the following Figure-10.

(heavily, moderate, and slightly) and the people toAs a result, managing everything from ground work

the evasion of defects.

to concrete in the inspection of construction process,

It is a defect of 30 million yen or less in the repair

and adjusting from the plasterer to the metal bycost including the subsidence etc., and the incidence

insurance become the optimal.

of a heavy defect becomes 0.6%.
It is a defect of five million yen or less in the repair( B i l l i on y en)\350
Quality (construction) control cost
Quality (repair) insurance costSocial cost
Citizen's senses of trust\300

cost including the inclination etc., and the incidence\250

of a moderate defect becomes 1.2%.

\200
\150

It is a defect of 500,000 yen or less in the contained\100

repair cost including the leaking of rain etc., and the

\50

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ee

co

Fr

( F a ctor)

ec

The repetition part has been generated in the range

El

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ct
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M i ti y e ip m la c oneqh i in u ip n t
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P r r w i pm tec qe
R o a s u ip n t
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a n on nt
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on n
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et et
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fo
rm
Ea Re
rt b aRo h w r
ck or
r ip krap\0incidence of a slight defect becomes 8.2%.

Air-of the defect, for instance a serious defect in a basicpart is contained from the crack if it is concrete.

Figure-10: Social cost including citizen’s senses of
trust

Here, it questioned about hearing to quantify
citizen’s senses of trust. It listened how much would
be able to be paid to evade each defect (heavily,

Qualitycontrolsysteminconstruction

moderate, and slightly) from the content of theindustryquestionnaire.

The optimal construction management level by

As a result, it is 180,000 yen a person for a heavy

which the social influence related to the quality

defect, 80,000 yen for a moderate defect, It is

securing can be decided by adding the index of

approximately 40,000 yen that a householder iscitizen’s senses of trust as a social benefit. It is

willing to pay was obtained.

thought that the demand level changes depending on

It is assumed that the total of citizen’ senses of trust

the used period and the investment scale of the6building. Generally, it is guessed that the demand

construction of insurance system to minimize social

level rises by these indices in large. Moreover, it iscost and to fill reliance that the people request

thought that the demand level of the sense of trust is

becomes possible.

also different in the building etc. that the corporation

A heavy defect and the moderate defect can bebuys the office building and the individual buy thecontrolled in the inspection of construction process

house. Making the social benefit of function inby the third party, and the construction control costwhich these are assumed to be a variable is needed.

of a household becomes 162,500 yen if it thinks at

It is necessary to design the insurance system

the construction management level of the caseaccording to the optimal construction management

including citizen’s senses of trust.

level by which citizen’s senses of trust are

And, about 42.6 billion yen is dropped below in

considered as a social benefit.

400,000 households, counted from the calculation of

About the improvement of all the defective qualities

the total of the generated repair cost according to thethough it is impossible, higher cost and longer time

division process by the number of housing, and it

are required for the improvement of the quality

becomes 106,535 yen a household for insurance.

control system. Therefore, it is reasonable to pay theConsequently, it is assumed that the construction

one with a low repair cost by the quality insurance

management level and the insurance system be madecost (insurance). It is not done as the object ofan obligation.

quality (construction) management system. ApplyingAnd,

the quality control concept similar to factory

responsibility and adoption of client side, insurance

products by introducing insurance becomes possible

is assumed for the constructor, the system thatthough factory products are the job-order production

proposes it by paying about 300,000 yen (The ratioof the different article.

to architectural expense is 1.5 %.) per housing. The

In the insurance system, the client consists of theconstruction system and insurance are greatly

payment of the repair cost corresponding to theameliorable.

generation

quality

If Insurance is paid by constructors, ranking systemcorresponding to the construction management level.

based in their records is necessary to set suitable

Fair insurance

insurance rate.

ratio

of

the

defective(insurance rate fee equal to thetheconstruction

control

cost

is

be

expected value of damage) will be collected in theinsurance mathematical principle. However, theThe quality control system based on a proper level offrequency and neither scale nor the repair cost iscontrol of construction intended for the entire

made public as required for the defective quality.

building in Japan and the insurance system can be

Basic date of the setting of insurance should be madedesigned best by using a social cost in which thedata base according to the kind and the scale of thesocial convenience function related to quality control

building.

cost function proposes by this research, quality
insurance cost function, and citizen’s senses of trust
is totaled.
The level of control of construction demand from

4. CONCLUSION

the building in Japan is requested by deriving each
In

this

research,

management

level

decisiontoofminimize

construction

cost function by doing people's demand for thesocialdefective quality rate and the sense of trust in

cost,
7

marketing.
It is possible to recover the trust of the constructionindustry by applying the above mentioned method of
the construction management level proposed by thisstudy and the insurance system in various buildings
or constructing industry in the future.

REFERENCES
Sadakazu,

ANDOU,

Yoshitaka,MATSUMURA,

1981. Introduction to statistical quality control forengineer, Kyoritu.
Yuichi,TATANA,

Yoshirou,

TAKAGI,

2005.

Diagnosis of the economy of disaster prevention
Measure and evaluation of risk management,
Keisou.
Housing reform ・ Dispute processing support
center,2004. Consultation statistics annual report
2004, Kaisei.
Housing reform ・ Dispute processing support
center,2005. Consultation statistics annual report
2005, Kaisei.
Yasunori, MATSUFUJI, Hiroshi, NAKAMURA,
2003. Architectural construction ・ Management,
Asakura.
RIBC Research Institute on Building Cost, 2006.
Multiplication manual of public, architectural repair
work, Taisei.

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