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					Ekanayake & Ofori                                 1

Lawrence Lesly Ekanayake (Postgraduate. Student),
George Ofori (Professor)
Department of Building, National University of Singapore 4 Architectural Drive Singapore 119260., Tel: (+65) 8743421

Although waste minimization is identified as one of the key factors for achieving
sustainability, the relative significance of construction waste sources and a comprehensive
waste assessment system have yet to be developed. Implementing any successful waste
minimization strategy during project execution requires the assessment of waste. Waste
minimization has to be embedded as one of the project objectives for that lead to
An objective of this research study was to identify the most important sources of waste in
construction and possible measures towards waste minimization in Singapore where
construction is recognized as a major contributor to waste in landfill sites. The study was
based on a postal questionnaire study of the larger construction firms. Design, operational,
procurement and material handling attributes that lead to site waste were evaluated using
statistical techniques. The study found that design changes while construction works are in
progress is the most significant cause of waste generation at site. It is concluded that there is
a need for the design and construction teams to interact closely to avoid unnecessary waste
related to design problems. This would lend support to the country’s effort towards
sustainable development.
Keywords: construction waste source, minimization, sustainability

The environmental implications of construction activity are now well known. The construction
industry in particular and the built environment in general has been found to be among the
main consumers of resources and energy. Moreover, the construction sector is reported to
be generating unacceptable levels of material waste. In addition, it is well recognised that the
Singapore construction industry has low productivity1 compared to the other sectors of the
economy, such as manufacturing. The level of abortive work, due to a high extent of
subcontracting is considered as a contributing factor to this phenomenon2. The vision
outlined for the Singapore construction industry in the “Construction 21” blueprint is to
become a “world class builder in the knowledge age” by, among other things, eradicating low
productivity and undesirable waste generation which were reported to be prevalent in the
construction industry.
This research study was undertaken to identify the factors which are responsible for the
waste generated on construction sites in Singapore. This knowledge would guide waste
minimization attempts at both the design and construction stages.

Construction waste can be divided into three major categories: material, labor, and
machinery waste. However, material wastage is of more concern because most of the raw
materials from which construction inputs are derived come from non-renewable resources.
Although “waste” is a familiar term in the industry world-wide, it is difficult to compare
construction waste figures from different construction sites due to a number of reasons,
including the use of varying definitions; and the use of different estimation approaches, by
different groups.
For this research study, the following definition of construction materials waste was adopted:

          Proceedings: Strategies for a Sustainable Built Environment, Pretoria, 23-25 August 2000
Ekanayake & Ofori                                2

  “Any material, apart from earth materials, which needs to be transported elsewhere from
  the construction site or used within the construction site itself for the purpose of land
  filling, incineration, recycling, reusing or composting, other than the intended specific
  purpose of the project due to material damage, excess, non-use, or non-compliance with
  the specifications or being a by-product of the construction process.”
Studies at the Building Research Establishment (BRE) in the 1970s established that waste
levels were not necessarily related to the type of construction or the building company but to
the site and the people engaged in the particular project3.


           Project consideration: Profit loss               With economic development, there is
                                                            an increase in the volume of
                           Delay                            construction and demolition activities.
                                                            The resulting rising amount of
                         Waste                              construction and demolition waste has
                                                            caused serious problems both locally
        New                                  Rework
                         Handling                           and globally.
                                                            The waste problem can be categorized
 Environmental and sustainable considerations
                                                            simply into two groups: (1) problems at
      Recycling            Reuse          Compost
                                                            the project level; and (2) problems at
                                                            the national level. Figure 1 illustrates
                        Incineration                        the relationship between these two
                                                            categories.     At the project level,
                          Landfill                          construction waste directly affects the
                                                            contractor’s profit. On the other hand,
       Figure 1: Waste Problem (Authors 2000)               construction waste leads to complex
                                                            environmental issues relating to waste
                                                            handling and disposal at the local, and,
in the case of Singapore, the national level.

The level of waste at construction sites is considerable. Studies 4 show that the waste rate in
the Brazilian construction industry is 20 to 30% of the weight of total materials on site. On the
other hand, work in the Netherlands found that the amount of waste for each building
material lies between 1% and 10% of the amount purchased,5 depending on type of material.
Further, it was concluded that an average 9% (by weight) of the purchased construction
materials end up as site waste in the Netherlands. Moreover, whereas the waste problem is
well known, it seems not to be given the recognition it deserves. One reason may be the
tendency to underestimate waste levels. Past studies have found that, most of the time,
actual percentages of site waste generation have been much higher than the initial
recommended waste norms for the projects. In the UK, the BRE studied the waste levels for
specific materials on 230 different building sites and found that the actual waste level is
consistently higher than the estimated level for all materials studied6. New purchases to
replace wasted materials, rework to correct mistakes, delays, and dealing with generated
waste cause heavy financial losses to the contractor.

Quantification practices in many countries treat construction waste together with demolition
waste. The proportion of the t tal waste generated contributed by construction waste and
demolition waste is difficult to generalize. Moreover, it tends to vary. It is reported that in the
US, demolition waste is at least double the content of construction-related waste7. The total
amount of waste generated in the construction industry is a significantly high proportion of
the total. It is reported that construction waste constitutes 26%8 of the total amount of waste
produced in the Netherlands and 29%9 of the solid-waste stream in the USA. This waste

         Proceedings: Strategies for a Sustainable Built Environment, Pretoria, 23-25 August 2000
Ekanayake & Ofori                                 3

poses major problems during disposal. It is reported that construction and demolition (C&D)
waste constituted about 65% of landfill space in Hong Kong in 1994/95 when it was at its
peak10. It is also estimated that construction activity generates approximately 20-30%11 of all
waste deposited in Australian landfills, and 50%12 of the waste deposited in a UK landfill.
Corresponding figures for Germany, and Helsinki, Finland are 19%13 and 13-15% 14
In Singapore, construction site waste is a major problem owing to the scarcity of land.
Although figures published by the Ministry of the Environment put only “construction debris”
in a separate category, and show that it is 5% of the total amount of waste, to encourage
more responsible practices, disposal charges have been raised a number of times in the past
decade. With the passing of the Environmental Public Health (Amendment) Act 1999, the
legislation has been tightened, with stiffer penalties, to dissuade illegal dumping of wastes,
an action for which construction companies are among the main culprits.

Many factors contribute to construction waste generation at site. Waste may occur due to
one or a combination of many causes. G         avilan and Bernold15 organized the sources of
construction waste under six categories: (1) design; (2) procurement; (3) handling of
materials; (4) operation; (5) residual related; and (6) others. In this research, the factors
which cause waste on site were identified after a review of the literature, and placed in four
major sources as shown in Table 1: (1) design, (2) operational, (3) material handling and, (4)
procurement, mainly for the practical purpose of the survey.
                 Table 1: Sources and causes of construction waste (Authors 2000)

 Design                                Operational                    Material handling      Procurement
 * Lack of attention paid to           *Errors by tradespersons       *Damages during        *Ordering errors
 dimensional coordination of           or laborers                    transportation         (eg., ordering
 products                              *Accidents due to              *Inappropriate         significantly
 * Changes made to the design          negligence                     storage leading to     more or less)
 while construction is in progress     *Damage to work done           damage or              *Lack of
 * Designer's inexperience in          caused by subsequent           deterioration          possibilities to
 method and sequence of                trades                         *Materials             order small
 construction                          *Use of incorrect material,    supplied in loose      quantities
 * Lack of attention paid to           thus requiring                 form                   *Purchased
 standard sizes available on the       replacement                    *Use of whatever       products that do
 market                                *Required quantity             material which are     not comply with
 * Designer's unfamiliarity with       unclear due to improper        close to working       specification
 alternative products                  planning                       place
 * Complexity of detailing in the      *Delays in passing of          *Unfriendly
 drawings                              information to the             attitudes of
 * Lack of information in the          contractor on types and        project team and
 drawings                              sizes of products to be        laborers
 * Errors in contract documents        used                           *Theft
 * Incomplete contract documents       *Equipment
 at commencement of project            malfunctioning
 * Selection of low quality products   *Inclement weather

145 questionnaires were sent by mail in November 1999 to all the building contractors
registered under the three highest financial categories (G6, G7 or G8) of the Building and
Construction Authority (BCA) in Singapore. The categorization of firms in the register is
based on their track record, financial resources and manpower capacity of the companies.
The firms in the top three categories were selected because, together, they represent the
larger portion of construction activities in Singapore. Moreover, firms in these financial
categories are required to be ISO 9000 registered before they can be registered.

          Proceedings: Strategies for a Sustainable Built Environment, Pretoria, 23-25 August 2000
 Ekanayake & Ofori                                   4

Contractors were requested to indicate their response based on their past experience of
building construction projects. The responding contractors were asked to mark each
attribute’s contribution to the probable site waste generation on a five-point scale: 1-“Of no
significance”’ 2-“Of less significance”, 3-“Significant”, 4-“More Significant”, 5-“Most
Forty-three successfully completed questionnaires were received from 43 companies,
representing a 30% response rate. 95% of the responded companies were certified to ISO
9000, and the remaining firms were in the process of seeking certification.

The responses were analyzed using SPSS statistical software. The analysis of source
ranking were carried out by the technique of Compare means by One Sampling T-Test. Test
value 2 was used to compare the means because above the test value (2) is considered as
“significant” or “more significant”. It was found that most of the pre-selected attributes were
significant contributors to site waste generation. The analysis was carried out independently
for each question. The results are presented in Tables 2 to 6, where a high t-Values
represent the most significant attributes under the category concerned.
Table:2            DESIGN                             Table :3      OPERATIONAL

               Design Attributes                 t-Value                                                  t-
                                                                       Operational Attributes
 Design changes while construction in                                                                   Value
 progress                                                   Damages to work done due to subsequent
 Inexperience of methods / sequence               9.55      trades
 Lack of attention to dimension                   8.84      Errors by trades persons or laborers        9.83
 Lack of knowledge about standard sizes                     Required quantity unclear due to improper
                                                  8.36                                                  7.57
 available at the market                                    planning
 Lack of information in the drawings              7.39      Delay of passing information to the
 Complexity of detailing                          6.88      contractor
 Incomplete contract documents at the                       Use of incorrect material, thus requiring
                                                  5.55                                                  5.95
 commencement of project                                    replacement
 Errors in contract document                      5.51      Accidents due to negligence                 5.52
 Selection of low quality products                5.37      Malfunctioning of equipment                 1.14
 Unfamiliarity of alternative products            5.07      Inclement weather                           0.96

Table:4 HANDLING                          Table:5 PROCUREMENT Table:6 SITE WASTE
DISCUSSION                                                                                                t-
                                                                          Waste Preventing Attributes
        Material Handling                                          Proper storage facility              11.59
                               t-value         Procurement    t-
           Attributes                                             Accountability system for sub
                                                 Attributes Value
Inappropriate storage           7.90       Lack of                contractors’ for extraordinary        10.20
                                           possibility to         waste
Material supplied loose         7.33                        6.56 Effective waste accounting
Damages while                              order small                                                  9.46
                                5.78       quantity               system
                                           Ordering errors         Selecting proper equipment and
Unfriendly attitudes of                                                                                 8.98
                                5.19       (too much or too 5.82 qualified operators
project team and laborers
Use of materials which are                 little)                Having an updated plans /
                                4.60                                                                    6.66
                                           Purchase not           Schedule
close to work place
                                           comply with      3.70 Employ material controller             6.14
Theft                           2.88
                                           specifications          Improve site security

The best way to manage waste is to avoid it in the first place. The study revealed that a
substantial amount of building construction waste on site is directly related to design errors or
related problems on which the site personnel have very little or no influence. Design changes
while construction in progress, designer’s inexperience or lack of data to evaluate methods

             Proceedings: Strategies for a Sustainable Built Environment, Pretoria, 23-25 August 2000
Ekanayake & Ofori                                5

and the sequence of construction at the design stage were ranked as the most significant
factors leading to site waste. However, lack of attention paid to modular coordination and
lack of knowledge about standard sizes of products on the market were also reported as the
next most significant contributors to site waste which are related to the design process. This
underlines the urgent need for effective communication and flexible information sharing
systems throughout the construction process.
Damages due to subsequent works, errors by tradespersons and improper planning were
identified by the responding contractors as the most significant operational contributors to
waste generation while inappropriate storage facilities at site and loose forms of material
supply to the site were identified as the most significant handling issues. The responding
contractors did not consider procurement-related factors as major contributors to site waste
generation in the Singapore construction industry.
The contractors believed that providing better storage facilities at site, making sub-
contractors responsible for their own waste generation, applying better site waste accounting
systems, and selecting qualified people and correct equipment for the site works will help for
reducing existing waste generation level.

It is necessary to promote appropriate clients’ project procurement systems where
contractors’ experience in methods and sequence of construction can help in the decision-
making process during the design stage to avoid unnecessary extra work during construction
which cause time delay and material wastage. This would contribute to the avoidance of
design changes which contribute to wastage.
Contractors must be educated about possible cost savings from measures which
successfully prevent construction waste, as well as the environmental impacts of the waste
and the its long-term national and global implication. The merits of waste minimization and
environment protection must also be promoted to clients. The reflection of these issues
among the client’s objectives would contribute significantly to the reduction of waste levels in
construction in Singapore.

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         Proceedings: Strategies for a Sustainable Built Environment, Pretoria, 23-25 August 2000
Ekanayake & Ofori                                6

    integration (Proc. R’99 World Congress, Feb 2         -5), A. Barrage & Y. Edelmann, ed.,
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         Proceedings: Strategies for a Sustainable Built Environment, Pretoria, 23-25 August 2000