The optimum use of construction knowledge and experience in planning, design, procurement and field operations to achieve overall project objectives” Construction Industry Institute (CII) definition of constructability.

Basu (2007) understood the preconstruction benefits of using 4D scheduling. He noted its particular help in complex phased and live construction site. In fact, whilst perhaps over stated, the case study suggested the “project could not be done without the initial detailed planning and buy-in using the 4D model”. However, there is no doubt that even in 2007 with considerably inferior and more expensive software, it was becoming increasingly obvious that BIM could help in making the construction of complex projects more efficient.

“Virtual Construction” (McCuen 2008) facilitates improvements during the development phase of the project. The knowledge the professionals bring together in producing the 3 & 4D models help during the constructability review. This includes suggestions from all team members. Perhaps insitu concrete may be cheaper to buy, but steel may be significantly easier to construct certain structures in.

(Wickersham 2009) “ Both the architect and the CM will work more intensively prior to the creation of construction documents, and they will share information more freely with each other throughout the process, in order to test the cost and constructability of design.” This process includes the use of 4D scheduling but also refers to the use of an integrated project delivery (IPD) approach. This approach advocates the sharing of risk and reward among the project team. But even without IPD, the BIM process lends itself to constructability reviews.

Perhaps one of the most obvious constructability tools is that of running several alternative designs and testing their constructability utilising the scheduling of the differing components of the designs. The relative ease of this process in comparison to the previous 2D process is staggering. It also allows designers and contractors prove the validity of some of their assumptions without having to learn from physically constructing them or from previous mistakes.

The 4D CAD model is a powerful tool for analyses and decision support (Benjaoran and Bhokha, 2009). They go on to list many of the same topics which have been previously discussed under visualisation and will be further discussed under the proceeding headings, showing the integrated nature of the BIM process. “Topics such as time, working space, sequences and temporary structures” which are all part of constructability reviews. These topics are further explored by (Akinci et al 2002) and (Ma et al 2005)

It has long since been appreciated that constructability can lead to a greater return on investment. In fact, the business roundtable reported a potential saving of up to 10:1 by applying constructability. “The idea was to minimise the gap between what designers draw and what contractors execute on site” (Hijazi et al 2009). Even prior to the use of BIM, Russell and John (1993) analysed case studies which proved savings in time of over 10% and in project cost of over 7% could be realised using constructability practices. These benefits can be to designers, contractors, owners and end users alike. All too often, owners do not get the product they wanted. This is often because they or their designers have interpreted the requirements and the designs differently. Again, Hijazi et al (2009) noted the potential of BIM when fully utilised with 4D scheduling, as a means of testing different design and sequencing alternatives. Differing professions rated the importance of certain benefits differently but all agreed that the use of constructability reviews could help in cost, quality, safety and time among other potential benefits.

The method of procuring projects can be a distinct driver in whether constructability reviews ever take place. In Ireland, the likelihood of a stringent constructability review taking place for a traditionally procured public project are very slim. This is for several reasons, such as having no contractor input during design, limited collaboration between the different professions and a lack of experience in using collaborative tools such as BIM. Regardless of this, the current climate in Ireland does not offer designers sufficient incentives or time to design buildings fully, despite to original intention of the GCCC forms of contracts requiring construction projects to be designed right down to the paint colours. The GCCC form of contract is conflictual in nature and does not lend itself to any form of collaboration between parties. The irony being, that the easiest way to reduce conflict and to ensure the completeness of the design process would be to carry out constructability reviews using all stake holders.

Some design and build projects under the public purse in Ireland do benefit from the use of constructability reviews, however, these do not generally include the end users or owners but are done by the contractor and design team to maximise profit but not necessarily produce a better product for the client. This lack of input by the client is a glaring omission from the process.

In Ireland there is no specific requirement for constructability reviews and thus they are often completed on an ad hoc basis. In Hong Kong, Singapore and Malaysia, systems for scoring buildability have been developed. Buildable Design Appraisal System (BDAS) was introduced by the Singapore Government and Buildable Multi-Attribute System (BMAS) by the Malaysian Government. Many other models predated and preceded these.



In the case of Sutter Medical Center Castro Valley, there was a full IPD approach to the project due to time constraints and the impending deadline to meet specific legal requirements with regard to earthquake protection. The team entered into a formal IFOA (Integrated Form of Agreement). This form of agreements included a share pain and share gain approach. There were profit sharing incentives for finishing on time and ahead of budget. There was a guaranteed maximum price and it was estimated, Khemlani (2009) that due to this integrated approach and continued constructability reviews, that the project was constructed 30% faster than a traditional approach. The design time for the structure alone was reduced by 7 months from 15 months to just 8 months. There is also little doubt that the 4D modelling can help in operational flows. Large idle machinery or hired structures and resources become very evident when they can be visualised. The safety aspects will be discussed in more depth but can also be mentioned under the efficiency savings possible through implementing constructability practices. 

Olatunji et al (2010), cited the improved accuracy in both the model, the quantities it produces and the live interactive updating of these quantities as changes are made as a means of ensuring greater confidence in the project at large. In addition to this, the greater accuracy leads to fewer assumptions and thus less contingency or float requirements. The mistakes found in the initial review of the Honam High-Speed Rail prior to any construction occurring show the enormous potential of using this process. However, the scale of the projects need to be taken into consideration when deciding to use the BIM process in an Irish context in the current climate. Firstly, due to dramatically decreased fees, many design and professional consultants are struggling to survive at all. They simply do not have the money to spend on new software and considerable training in BIM. At the moment, it is arguable that whilst clients believe they are getting design fees at the best value ever, they are unaware that the deficiency in design due to decrease resources being allocated is in fact probably leading to more expensive types of buildings. The easiest way to design is to over design. In architects cases it may simply be spending less time investigating alternative products and more modern solutions. In engineering terms it may be allowing larger size beams and columns rather than pursuing greater analysis in connection details or composite actions.

There is a considerable irony in the fact that many people cannot afford the cost of up skilling and investment in technology due to limited financial resources within the country and sector given that this investment could help dramatically reduce costs to all parties. At with visualisation being a benefit to the teaching of construction courses, so too is the ability to give students, who otherwise may have little experience or knowledge of construction, a building model in 4D. It allows students see much of the sequencing and methodology of construction and project management. It also affords the students the ability to actually construct a project and work through the sequencings following the logic with class tutors and those with greater experience. It has the potential to change dramatically the way construction is taught and could result in far more knowledgeable construction managers coming out from future courses. It has long since been a complaint of the industry that students who leave college simply do not have a realistic understanding of the problems they will encounter and how to deal with them. This is strongly argued by Thomas and Mengel (2008) as well as Peterson et al (2011).

 Finally, in its most simplistic form, as alluded to by Deutsch (2012), 4D models and schedules help people understand how things are put together. They help designers understand the consequences of many of their choices. This is perhaps one of the most valuable benefits of 4D. It removes much of the previous disconnect between designers and contractors. We are all aware of comments when some very difficult detail to construct arrives on plan. In general these comments are about the lack of time designers have spent at the cold face of construction. In such a fast paced specialised construction industry, it is very hard for all professions build up on site experience. This is why 4D models can help all parties understand each other.