Factors Affecting Buildability of Building Designs

Keywords: what is buildability, principle of buildability construction

Buildability is increasingly become a major requirement in building construction practice. The aim of buildability is use to improve the efficiency of overall building process by developing construction sensitive designs.

Nowadays, in Malaysia construction industry, there have facing a lot of problem that will impede the project to process smoothly. In this research, it will highlight what buildability is. Through this we can deeply understand what buildability is and how important it was in the construction industry.

Moreover, in this research, we wish to find out and identify the buildability attributes in building design in Malaysia construction industry. There are many buildability attributes have affecting in the building design. If the constructions proceed without a good buildability management, it will bring many problems to the project. So in this research, besides that identifying the buildability attributes, we also wish to find out the importance level for each of these attributes.

AIM

This report are aim to find out the factors that affect buildability of building design in the Malaysian construction industry.

OBJECTIVE

• In order to achieve the aim of the report, the following are the objectives of this research
• To study what is buildability and factors may affect it in building design
• To find out and identify the buildability attributes in building design in the Malaysian construction industry
• To measure the level of importance of different buildability attributes

Research Methodology

Literature Review

The purpose of the literature review is given us to understanding what buildability in the construction industry is and how important it was. This research methodology may include definitions, ideas and practices of related topics. Besides that, we can study and review to the relevant books, journals, internet and etc., as known as secondary data, that related to the topic – buildability. Through those review sources, the important point will be noted down and convenience for us to writing the literature review.

The below are showing that the literature search that will be carried out:-

• Define the definition of buildability/ constructability
• Define the principle and concept of buildability/ constructability
• Determine the factor affecting buildability in building design in construction
• Determine the building attributes and the level of importance for each attribute

Questionnaire

Questionnaire is recommended as one of the research method, because it is easier for analyzing the data, economical and the hypothesis can be tested. Questionnaire is a research instrument consisting of a series of questions and/or in difference grouping for the purpose of gathering the information from respondents.

To gain more information of this research, copies of questionnaire will be sent out to the construction companies and they are needed to express their opinions based on their experience. In this questionnaire, there are empty spaces provide for the respondents to giving their comment or suggest other building attributes which are not included. This questionnaire will target to the professionals such as architect, engineer, project manager, quantity surveyor and others in the contractor industry firm in Malaysia.

From the research title, to determine the level of importance of buildability attributes in this research, the classification of the rating scales is used. The questionnaire is based on LIKERT SCALE format. It is a widely used instrument in measuring opinions. A likert item is simply a statement which the respondent is asked to evaluate according to any kind of subjective or objective criteria and generally the level of agreement or disagreement is measured. 5 point likert scale being used as it may produce slightly higher mean scores relative to the highest attainable score.

This will be carried out in the final stage of research methodology. The results/ comments get from the respondents will be analyze and present in table or graph in order to provide a clearer view of overall research with writing up the contents of the dissertation. Besides this, analysis and interpretation would be done to gather all the information and data.

DISSERTATION ORGANIZATION

• Chapter 1- Introduction

Chapter 1 provides an introduction of the chapter that giving a brief about our proposal. In this chapter it includes introduction/ background, problem statement, aim, objectives, research methodology and working program for the dissertation.

• Chapter 2 – Literature Review

Through the review of literature/ articles related to our research topic the important point will be written in this chapter. Journals, books and information from the internet will be the source of the information or data to doing this buildability title dissertation. This chapter are aim to provide a main picture of the knowledge to us before the research is carried out.

• Chapter 3 – Research Design and Methodology

Questionnaire will be designed based on the objective and information that we want to find out. These questionnaires will be sent to different construction industry companies in Malaysia to collect data to conduct next step of dissertation.

• Chapter 4 – Data Analysis and Results Discussions

The collected information from the respondents will be evaluated and analyzed in table or graph with explanation.

• Chapter 5 – Conclusions

This chapter will conclude and recommend the overall results of the survey for further research.

REFERENCES

Crowther,.P. “Design For Buildability and The Deconstruction Consequences”, Design for Deconstruction and Materials Reuse, CIB Publication 272.

Lam, P.T.I., Wong, F.K.W., Wong, F.W.H. 2007. “Building features and site-specific factors affecting buildability in Hong Kong”, Journal of Engineering, Design and Technology, Vol 5, No 2.

Mydin S.H., Zin R.M., Majid M.Z.A, Zahidi M. and Memon A.H. 2011. “Buildability Attributes at Design Phase In Malaysian Building Construction”, International Journal of Sustainable Construction Engineering & Technology, Vol. 2, Issue 1.

Wong, F.W.H, Lam, P.T.I, Chan, E.H.W. and Wong F.K.W. 2006. “Factors Affecting Buildability of Building Design”, Canadian Journal of Civil Engineering, 33.7, pg 79

CHAPTER 2 LITERATURE REVIEW

INTRODUCTION

“Buildability” or “constructability” has a huge area of study and it was very important in a construction industry. The aim of these literature reviews are to study and highlight the area that the buildability attributes that may affect the building design in Malaysia construction industry.

The first reviews that will focus in this chapter are definition of buildability, then coming up with the principles and concepts of buildability which have defined by different countries. Moreover, this review also focuses on the factors that may affect the buildability by identify the buildability attributes in building design.

BUILDABILITY / CONSTRUCTABILITY

DEFINITION OF BUILDABILITY

Since the buildability is important in the construction industry, so there are many researchers from different countries has identified and defined buildability based on their studies.

Based on the several articles study and resources, it found that the one of the widely definition that can be accepted which is define by the Construction Industry Research and Information Association (CIRIA), 1983, it stated that the “buildability is the extent to which the design of a building facilitates ease of construction, subject to the overall requirements for the completed building” (Wong, Lam, Chan and Wong, 2006B.p. 796).

Besides the definition defined by CIRIA, there also have another definition which was founded with specific aim of improving the construction total quality management and the overall cost effectiveness and defined as “constructability is the effective and timely integration of construction knowledge into the conceptual planning, design, construction and field operation of a project to achieve the overall project objectives in the best possible time and accuracy at the most cost-effective level” by Construction Industry Institute (as known as CII) in year 1986 (Wong, et.al, 2006B.p. 796).

According to The Construction Industry in Australia (CIIA), Griffith and Sidwell (1997), has defined constructability as a system “to integrate if construction knowledge in the project delivery process and balancing the various project and environmental constraints to achieve the project goals and building performance at the optimal level.”(Wong, et.al, 2006B.p. 796)

Buildability Performance Research Group (BPRG), Chen and McGeorge (1994), defined buildability as “the extent to which decisions, made during the whole building procurement process, ultimately facilitate the ease of construction and the quality of the completed project” which buildability as a management to goals the project by recognize the factors affected the project (Eng, 2002.p. 117).

In the other hand, there are other researchers have derived their own definitions based on their studying in buildability, such as:-

• Ferguson (1989); buildability was defined as “the ability to construct a building efficiently economically and to agreed quality levels from its constituent materials, components and sub-assemblies” (Wong, et.al, 2006B.p. 796.)
• Williams (1982); buildability was defined as the “most economic and efficient way of putting a building together.”(Yang, 2004)
• Illingworth (1984); buildability was defined as “a design and details which recognize the assembly process in achieving the desired result safety and at least cost to the client.”(Yang, 2004)

In year 1996, Moore has modified the definition defined by Illingworth as a “design philosophy, which is recognizes and addresses the problems of the assembly process in achieving the construction of the design product, both safety and without resort to standardization or project level simplification.”(Yang, 2004)

Lueprasert (1996), constructability has defined as “an important characteristic of structural design and site conditions of construction project which determines the level of complexity of executing the correlative structural assembly tasks.”(Yang, 2004)

Moreover, there are few researchers believed that constructability are significantly different with buildability. The differences between buildability and constructability are that buildability is a design-oriented concept but constructability is concern the whole project processing. But also have some researchers thought that there are no difference between buildability and constructability, the only is buildability is usually used in UK and constructability is often used in USA. (Yang, 2004)

PRINCIPLES AND CONCEPTS OF BUILDABILITY

According to Eng, (2002, p. 112), “”Buildability” or “Constructability” has been used and evolved in the construction management in the late 1970″s in United Kingdom, but its potential was not been fully exploited in construction industry at the time.” Nowadays, buildability is increasingly become an integral part of the construction industry in many countries because it was a technique used to manage the construction process during the pre-construction stage. According to Low et.al, (2008), buildability aim is to ensure the impacts of design details are recognized and considered in the earlier stage to reduce and/or prevent errors, delays and allows a cost control to the overall project others. Together with this, it will enhance the productivity and competitiveness of the industry. Moreover, Low study also stated the summarized of buildability principles that defined by some researchers such as Adams (1989), Ferguson (1989), Gray (1984), Griffith and Sidwell (1995), Tatum (1987) and others as shown as below:-

Efficiency and economical building production; “to ensure efficient and economical production of a building, a logical organization of the sequence of assembly is necessary. The building organization must ensure continuity of construction work by having food management due to labors, machineries and materials delivery to achieve this principle (O’Connor, 1985).”

Simplicity; “this principles saying that the designers of the project must try to produce the simplest possible details compatible with the overall requirement for the building especially for the building’s group of elements (Ferguson, 1989; Bishop, 1985).”

Tolerance Level; “the building design should recognize its tolerances which are normally attainable under site conditions. Different the materials and components used on site have its different composition and different jointing methods required. Therefore, practical level of tolerance adopted is necessary for the materials and components (Ferguson, 1989).”

Innovation; “use any innovative ideas that can enhance the buildability of a project. The contractor should try to bring in new machineries or methods of working that can improve the productivity and allow construction process more efficiency. Before bring in the ideas, consideration of the level of skills available in industry is required. (Tatum, 1987).”

Proper scheduling; “a good scheduling of works may allow construction proceed smoothly and right on track. The construction sequence should be practical to allow for a continuous flow of work to minimize delays of works (Gugel and Russell, 1994).”

Repetition and standardization; “to reduce time consuming for constructions, the building elements should be design that encourages appropriate repetition and standardization, it may help to reduce cost, risk and error by using readily and standard items in construction (Adams, 1989; Ferguson, 1989).”

Participation and communication; “project team members with relevant knowledge should be encourage to participate all level of construction. They can give their opinion and suggestion during early planning stage to reduce problem in future. Clear project information should be planned and coordinated to suit the construction process and facilitate the best possible communication and understanding on site (Fischer and Tatum, 1997).”

Avoid damage by subsequent works; “the design should enable the works that carried out will not have risk of damage due to adjacent finished elements and with minimum requirements for special protection. This would reduce the need for return visits to site to repair damage. By doing few times checking to the completed works is better to reduce the project completion period (O’Connor and Tucker, 1986).”

(Source: Low et.al, 2008)

McGeorge and Palmer (1997) have identified that buildability and constructability is the only management concept to have been designed and developed by the construction industry (Eng, 2002). This is because they think that the separation of designs and construction processes is unique to the construction industry. Eng also mentioned that the report in early 1960’s, “division between the process of design and construction was recognized as contributing to inefficiencies throughout the construction industry.” (Eng, 2002).Emmerson (1962) has identified that insufficient documentation before tender, inefficient pre-contract design procedures and lacks of communication among the architects, consultants and contractors appointed are the factors that cause the problem occurred (Eng, 2002). Moreover, Banwell, (1964) suggested that “the contractor who is too far from the design stage for his specialized knowledge can be participate in traditional contracting situation.” (Eng, 2002.p. 111).In the other hand, Banwell report also highlighted that “the complexities of modern construction and its requirement for specialized techniques demand that the design process and the construction stage should not be regarded as separate fields of activity.” (Eng, 2002.p. 111)

EVOLUTION OF BUILDABILITY/CONSTRUCTABILITY CONCEPT

Through different groups of researchers, a number of stages in the evolution of the buildability or constructability concept are been identified and related to research efforts in different parts (Eng, 2002). According to Eng (2002) study, it shows the groups of researchers from different countries that have evaluated the evolution of buildability/constructability, which are:

• Construction Industry Research and Information Association (CIRIA); UK
• Construction Industry Institute (CII); USA
• Construction Industry Institute of Australia (CIIA)
• Building Performance Research Group (BPRG); University of Newcastle in Australia

“In the early research taken by CIRIA and UK researches, they regarded that buildability is problem that arose from the division between builders and designers; led researchers to focus on technical issue and site and construction planning (Gray, 1983; Adam, 1989; Ferguson, 1989).” (Eng, 2002.p. 112)

Besides that, Eng stated that most industry researchers and commentators are tended to see buildability as a function that is within the influence or control of the designer. Illingworth (1984) has suggested that “the problem of buildability was become deteriorate because the designers and professional team are resented contractors involve and giving their opinions during the design stage.”(Eng, 2002.p. 112)

In addition, CII had used industry case studies to investigate the constructability problem in construction industry to allow the researchers to understanding the issues. This carried out the understanding of different stages of project life cycle which would relate to different issues in constructability (Eng, 2002).

Furthermore, CIIA also used the case studies to enable a holistic perspective to be maintained. CIIA have proposed 12 principles would be relevant with different emphases due to the different project life cycle. For BPRG at University of Newcastle in Australia, they started with conceptualize the buildability problem as one that derived from a complex system and they proposed that the concepts of buildability is needed to recognize the factors in a project environment which may affected in the design process, construction process and the link between them (Eng, 2002).

CIRIA RESEARCH IN BUILDABILITY

The definition of buildability defined by CIRIA has shown at the above. Though that we know that CIRIA definition is focused between designs and construction; the factors has been implied which are solely within the influence or control of the design team those have a significant impact on the ease if construction of a project (Eng, 2002). The concept was recognized as an issue within an integrated design management context. A good buildability are formed based on a building design, structure or other which had been consider in the construction phase with emphasis on the method of construction, activities, sequence of works and way incorporated into the overall design (Eng, 2002).

In additional, Eng study had showing the 16 guiding principles for achieving buildability which was identified and developed by Adams (1989), CIRIA, as below:-

• Investigate thoroughly
• Consider accessibility at the design stage
• Consider storage at design stage
• Design for early enclosure
• Design for minimum time below ground work
• Suitable materials use
• Consider for the local skill available
• Design for simple assembly
• Plan for maximize repetition and standardization
• Maximize the use of plant
• Allow for sensible tolerances
• Allow for a practical sequence of operations
• Plan to avoid change to work
• Avoid return visits on site; do it right in first time
• Safe construction design
• Clearly communication

(Source: Adam, (Eng, 2002))

CONSTRUCTABILITY DEVELOPTMENT BY CII

According to Eng (2002), has mentioned that CII used case studies to identify different of requirements for the planning stage (Tatum et.al, 1986), engineering and procurement phases of a project (O’Connor et.al., 1986) and improvement of constructability that able to make during field operations (O’Connor and Davis, 1988). In additional, they had identified and presented 6 concepts for the planning stage, 7 concepts for the design and procurement phase and 1 for field operations phase which showing below:-

Conceptual Planning Stage

• Basic design approaches consider major construction methods
• Constructability programs are an integral part of project of project implementation plans
• Project planning requires construction knowledge and experience
• Early construction involvement in the development of contracting strategy
• Project schedules are construction sensitive
• Site layouts show efficient of construction

Design and Procurement Stage

• Design for accessibility, materials and equipment
• Design for construction in adverse weather and remotes locations
• Design and procurement schedules are construction sensitive
• Design to enable efficient construction
• Design elements are standardize
• Construction and procurement efficiency are specifications developed
• Design for modularization to facilitate fabrication/transportation

Field Operation

Contractors use innovative methods

(Source: Tatum et.al; O’Connor et.al; O’Connor and Davis; (Eng, 2002))

CONSTRUCTABILITY PRINCIPLES BY CIIA

For CIIA, they have review to the work of CII, and some developed construction information within the Australian context (Eng, 2002). At the beginning, they are 17 principles are being identified and tested. In the other hand, more than twenty of the personnel who experienced in construction are given feedback due to this tested. Through the test, Constructability Principles File (CIIA, 1992) has shown 12 concepts of constructability to represent current best practice applicable over five projects life cycle stages, which are feasibility studies stage, conceptual design stage, details design stage, construction stage and post – construction stage (Eng, 2002). The twelve principles espoused were:-

PRINCIPLES DESCRIPTION

• Integration

Constructability must be made an integral part of project plan.

• Construction Knowledge

Project planning must actively involve construction knowledge and experience.

• Team Skills

Project team must be appropriate for the project based on their experience, skills and etc.

• Corporate Objectives

Project team understanding against client”s corporate and project objective to improve constructability.

• Available Resources

Technology use in design solution must be matched with the skills and resources available.

• External factors

External factors might affect the cost and program of the project.

• Program of project

Overall project program must be realistic and have the commitment of the project team.

• Construction Methodology

Construction methodology must be considered in project design.

• Accessibility

Constructability will be improved if accessibility is considered good in the design stage of project.

• Specifications

Constructability improved when efficiency considered in specification development.

• Construction innovation

Constructability improved when innovation techniques is used

• Feedback

Post construction analysis is undertaken to allow constructability can be enhanced on future projects

Table Principles by CIIA (Francis and Sidwell (Eng, 2002))

CONSTRUCTABILITY CONCEPTS BY MALAYSIAN RESEARCHER

According to Nawi, Kamar, Lee, Hamid, Abdullah, Haron and Ariff (2009), stated that in Malaysia, the constructability and buildability concepts established by the Construction Industry Institute (CII) and other relevant literature by CIRIA, (1983); Tatum, (1987); Adams, (1989); CII, (1993) and etc, there are 23 constructability concepts were formulated and presented by Nima, (2001) which use them to utilize a study in relation to the engineered construction phases. There are 7 concepts for conceptual planning phase, 8 concepts for design and procurement phase and 8 concepts for field operation phases which as follows:-

C1-C7 (Project constructability enhancement during conceptual planning phase)

Concept C1 – the project constructability program should be discussed and documented within the project execution plan, through the participation of all project team members.

Concept C2 – a project team that includes representatives of the owner, engineer and contractor should be formulated and maintained to take the constructability issue into consideration from the outset of the project and through all of its phases.

Concept C3 – individuals with current construction knowledge and experience should achieve the early project planning so that interference between design and construction can be avoided.

Concept C4 – the construction methods should be taken into consideration when choosing the type and the number of contracts required for executing the project.

Concept C5 – the master project schedule and the construction completion date should be construction-sensitive and should be assigned as early as possible.

Concept C6 – in order to accomplish the field operations easily and efficiently, major construction methods should be discussed and analyses in-depth as early as possible to direct the design according to these methods.

Concept C7 – site layout should be studies carefully so that construction, operation and maintenance proceed efficiently and avoid any interference between the operations performed during these phases.

C8-C15 (Project constructability enhancement during design and procurement phases)

Concept C8 – design and procurement schedules should be dictated by construction sequence. Thus, the construction schedule must be discussed and developed prior to the design development and procurement schedule.

Concept C9 – advanced information technologies are important to any field including field of construction industry. The usage of those technologies could overcome the problem of fragmentation into specialized roles in this field, hence enhancing constructability.

Concept C10 – designs, with design simplification by designers and design review by qualified construction personnel must be configured to enable efficient construction.

Concept C11 – project elements should be standardized to an extent that will never affect the project cost negatively.

Concept C12 – the project technical specifications should be simplified and configured to achieve efficient construction without sacrificing the level or the efficiency of the project performance.

Concept C13 – the implementation of modularization and preassembly for project elements should be taken into consideration and studied carefully. Modularization and preassembly design should be prepared to facilitate fabrication, transportation and installation.

Concept C14 – project design should take into consideration the construction personnel, materials and equipment accessibility to the required position on-site.

Concept C15 – design should facilitate construction during adverse weather conditions. Great emphasis should be made to planning for the construction of the project under suitable weather conditions, but the designer must plan and take into consideration the project elements that could be prefabricated in workshops.

C16-C23 (Project constructability enhancement during field operation phases)

Concept C16 – field task sequencing should be configured in order to minimize damages or rework of some project elements, minimize scaffolding needs, formwork used or congestion of construction personnel, material and equipment.

Concept C17 – innovation in temporary construction materials/systems, or implementing innovative ways of using available temporary construction materials/systems that have not been defined or limited by the design drawings and technical specifications will contribute positively to the enhancement of constructability.

Concept C18 – incorporating innovation of new methods in using off-the-shelf hand tools or modification of the available tools or introduction of a new hand tools that may reduce labour intensity, increase mobility, safety or accessibility will enhance constructability at the construction phase.

Concept C19 – introduction of innovative methods for using the available equipment or modification of the available equipment to increase their productivity will lead to a better constructability.

Concept C20 – in order to increase the productivity, reduce the need of scaffolding or improve the project constructability under adverse weather conditions, constructors should be encouraged to use any optional preassembly.

Concept C21 – constructability will be enhanced by encouraging the constructor to carry out innovation of temporary facilities.

Concept C22 – good contractors, based on quality and time, should be documented, so that contracts for future construction works would not be awarded based on low bits only, but by considering other project attributes.

Concept C23 – evaluation, documentation and feedback of the issues of the constructability concepts should be maintained throughout the project to be used in later projects as lessons learned.

(Source: Nima el al, (Nawi, et.al, 2009))

Although there are many researchers from different countries have identified and presented their own principles and concepts, but the points they covered are almost the same. Through those principles and concepts, it showing the ways to help the construction to reduce its project time, error, cost by having a good buildability on manage overall project.

ASSESSMENT OF DESIGNS FOR BUILDABILITY

According to CIRC and Chiang et.al, has stated that the construction industries are continues to search out the ways to improve buildability, such as the use of prefabricated, standardized and modular components, as well as the adoption of alternative procurement methods (cited by Wong, Lam, Chan P.C. and Chan H.W., 2006), the Building and Construction Authority (BCA) in Singapore had introduced and published a Code of Practice on Buildable Design to explain how the Buildable Design Appraisal System (BDAS) works (Building and Construction Authority, 2005). They have quantified the buildability of designs based on 3 principles, which are “standardization”, “simplicity” and “single integrated elements” (Low et.al, 2008).

Besides that, according to Poh and Chen, Low, Lam and BCA, it mentioned that the “Buildability scores” (BS) has been represent in Singapore aim to saving manpower consumption on site. A design with higher the buildability scores will allow more efficient labour usage in construction, increase productivity and also the construction quality (cited by Wong et.al, 2006A). An overall buildability scores will be calculated based on the construction systems and also the finishing systems used, as well as building features, building services aspects and site specific factors that may affect in the building design. In calculating overall building scores, a set of buildability indices for different components of a design was used for the assessment (Wong et.al, 2006A).

BUILDABILITY ATTRIBUTES IN BUILDING DESIGN PHASE

There are many researchers has carried out many research of buildability such as buildability concepts, ,buildability principles and others which are related and contributing due to the buildability in design phases. Buildability attributes are very important in the building design stage, its aim to describe the characteristics which directly or indirectly integrated the construction knowledge in building process, limitation and others to maximize the project goals and building performance (Mydin, Zin, Majid, Zahidi, Memon, 2011). These buildability attributes mostly are modified from the principles and concepts and sub-divided into few headings of buildability factors and few key of buildability factors. Based on the articles review, there are 63 buildability attributes were developed through the interview and also some literature review which done by Franky W.H. Wong, Patrick T.I. Lam, Edwin H.W. Chan and Francis K.W. Wong. They have grouped those building attributes into 16 headings and divided into 2 categories which is (i) related to the design process and (ii) related to the output for the design process.

BUILDABILITY ATTRIBUTES DUE TO DESIGN PROCESS

• Site- specific factor

The type and selection of site is very important before the construction start because it may affect the buildability. To avoid delays and reduce problems cause during the construction process, the site and ground investigation should be carried out such as topography survey, cable detection and others.

• Below ground

The works which undertaken below ground should be careful considered to minimize the construction time taken on below ground, ensure the safety and minimize the effects of works due to surrounding building (Adams, 1989).

• Weather

During the earlier construction stage, consider the possible timing to avoid carrying structural work and external work to prevent hindrance and damage by bad weather (Adams, 1989; Nima et.al, 1999) such as in Malaysia, the monsoon season will affect the construction process.

• Innovations

The design solution encourages the usage of innovative ideas in the construction site activities, the use of temporary construction materials or systems to reduce use of labour, improve the project quality and safety performance (CIIA, 1996; Low and Abeyegoonasekera, 2001).

• Coordination and rationalization of design information

To facilitate the construction process on site, the design should allow for easy communication with the contractor at the workplace (Adams, 1989; Griffith and Sidwell, 1995). This attributes also consider the coordinating of drawings, specifications, specification updating and removing ambiguities or misunderstandings. By showing the accurate positions such as pipe sleeves or penetrations, it may easier the contractor for understanding the design and carries out the works.

• Detailing

The design details should be kept as simple and simplify to reduce the learning curve effect of site tradesmen, therefore it improve buildability. Moreover, the specification of the tolerances should be specified in reasonable. For example, sufficient tolerance needs to be specified to allow window frame fixed onto window opening without doing any adjustment or modification. Besides that sensible differentiation between factory tolerances and site construction tolerances, designers should allow for the problem of fit at the interfaces between different products (Adam, 1989).

• Flexibility

Flexible designs may allow contractors to select construction method before the construction proceed and allow making change according to actual site conditions encountered. Similarly, adaptable design with interchangeable components provides room for changes to suit different circumstances (Wong et.al, 2006B).

• Tools, plant and equipment

Designing with knowledge of plant, tools and equipments for optimize use of these items in construction site. Accessibility of those during in the design and construction stages is necessary for maximize constructability performance of the project (Adams, 1989; CIIA, 1996). Designing also for temporary plants and equipments which anchorages in permanent structure is important under this attribute.

• Materials, fittings, products and subassemblies

Designers should use widely available and easily converted materials that can be worked on quickly and economically for optimize buildability (Ferguson, 1989). Designing for locally or import available materials, fittings, products and subassemblies for construction must be proven suitable for the purposes to prevent waste or changes in future.

BUILDABILITY ATTRIBUTES DUE TO DESIGN OUTPUT

• Safety

Designers should be conscious of job-site safety during design stage (Wong et.al, 2006B). The designer should take consideration that provide a safe working environment, allowing safe sequence of trades and safety of workers during handling of materials and components for access is necessary (Adams, 1989).

• Site layout, access and environment

Designers should think over the access, environment and site layouts during designing to provide a good accessibility. For example, a construction conduct may influence nearby traffic conditions. It causes the vehicles hard to move in or out and inconvenience to them, allow sufficient passing way to overcome this problem. Moreover, designing for allow sufficient working space for workers and plants, measures to avoid damage and nuisance such as noise, vibration, chemical waste and etc. due to surroundings. The efficient location and distribution of temporary works and storage areas are also necessary for a good buildability (Ferguson, 1989).

• Use of resources

Seek out the methods during design stage will help to improve the buildability by designing for economical labour use, widely available and versatile tools, plant and equipment (Ferguson, 1989; Griffith and Sidwell, 1995; Nima et.al, 1999) to reduce overall construction cost. Furthermore, factors affecting the availability of resources and skills should be taken into consideration (CIIA, 1996). It was suggested that a realistic assessment of the levels of skill likely to be available from appropriately chosen contractors and specialists could be carry out to suit the skills available locally (Adams, 1989).

• Material systems

Optimize the usage of material to prevent wastage and improve buildability in the construction. Unifying the choice of materials can help to achieve ease of construction because coordination problems were likely to arise from designs that involve many different types of materials (Griffith and Sidwell, 1995). Select suitable material based on their size during design may help to minimize labour requirements and also the wastage cause by cutting works (Griffith and Sidwell, 1995).

• Installation sequence

Designers should produce the simplest details compatible with the overall requirements for the building to maximize the building performance (Wong et.al, 2006B). Building designs with simple configurations enable the works become easy and facilitate ease of the construction (Wong et.al, 2006B). However, this aspect must be balanced with the aesthetic requirement of clients and artistic aspiration of designers (Mydin et.al, 2011). Allowing easy connection/interfacing between components, easy installation and flexibility in erection/trade sequences also the one should consider under this attribute.

• Standardization

Standardization is the process of developing and implementing technical standards. It also known as the one of the 3 key principles of the Buildable Design Appraisal System (BDAS) that devised in Singapore to measure buildability performance of designs (Wong et.al, 2006B). Standardization refers to the repetition of grids, sizes of components and connection details (Wong et.al, 2006B). For example, columns or external claddings work with repeated sizes will reduce the number of mould changes (BCA, 2005). In the same time, standardization helps improving the productivity, quality, reducing project cost and reducing duration to the construction (CIIA, 1996).

• Prefabrication

Prefabrication is the practice of assembling components of a structure in a factory or other manufacturing site and transporting the complete assemblies or sub-assemblies to the construction site. For example, use of precast components may reduce on-site operations; therefore improve productivity (BCA, 2005). By using both standardization and prefabrication together would facilitating better management (Gibb, 2001).

(Source: Modified from Wong et.al, 2006B)