Traditional or conventional construction is based on-site and all building processes are linear such that they are largely (up to 90%) undertaken on the site. The construction is undertaken in phases and every process is completed before moving onto the other. On the other hand, modular construction is based mostly off-site and most building processes can be simultaneous. For example: manufacturing of modules in plants can be undertaken side by side of excavation for foundation on site. In modular construction, individual components or entire modules are constructed in the factory, transported to the site and are assembled completely or mostly on site.
In this article, we will take a look at the construction industry today and relevant studies that compare the two methods. We will examine the various factors or aspects of both construction methods in detail. The need for affordable housing and better standards of safety are two important parameters that drive the decision to choose modular construction over traditional. We will therefore examine several factors that discuss the pros and cons of Modular vs. Traditional:
- Project duration
- Project Quality and Productivity
- Project Cost
- Project Safety
- Project Complexity and associated costs
- Project Planning and
- Environmental Concerns
These are the most important determinants for stakeholders who want to choose between the two methods of construction in the industry. The conclusion will discuss ‘How and When to choose one building method over the other’.
Construction Industry – An Overview and Recent Studies
The construction industry is constantly aggrieved by several recurring issues such as environmental pollution, shortage of labor, lack of productivity, financial issues and such. These issues are affect the global construction industry and we are constantly looking for methods and ways to overcome them. Considering the several benefits and limitations of various methods of construction, today the global attention is clearly divided between modular and traditional construction. Modular construction does trump over traditional in several aspects we have mentioned above, but there are still some challenges to be overcome.
Especially in the past several decades, the study of the differing aspects of these methods has been conducted by several researchers. On the one hand, the implementation of modular construction has vastly risen in the past decades . It has been accepted by experts that in the next 20 years, modular building can overcome most challenges and enhance productivity in the construction industry if undertaken in a proper manner . On the other, several studies such as that of  suggest that experience and the presence of trained and skilled workers plays an important role in deciding whether to adopt traditional or modular construction. The research of Choi  indicated that there is a reasonable co-relation between the factors that impact the success of modular construction project and the project productivity. The study of O’Connor et al.  indicated that when a construction project has a time constraint, modularization can be a useful method for completing the project in the allotted time. This can be due to the project not having delays due to any accidents or hazards as all the production of modules is undertaken in a protected environment.
Modular vs. Traditional – What are the pros and cons?
The duration or the project schedule is a very important factor of comparison of both methods especially for projects that run on severe time constraints. These can include projects that meant for rehabilitation after a flood or a hurricane as well as time bound projects such as hospitals etc. The time saved on a project directly translates to economic savings that is also a major determinant for the mode of construction being chosen. In a study conducted by , the modular construction is found to have a 58% advantage in terms of project delivery duration, compared to conventional construction which drastically brings up the productivity of the project.
In modular construction several building processes can be performed simultaneously and there is lesser delay caused by weather conditions  . In traditional brick construction, the building processes are linear and performed one after the other. Any delay in one process will create an overall delay in the entire project. Also all or most building processes are carried out on the site and are hence prone to delays due to bad weather or vandalism. In a study , it has been determined that modular construction requires up to 40% less time than traditional construction methods.
Project Quality and Productivity:
Right from the process of design to manufacture and building on site, there are several aspects that affect the end quality of a project. The productivity of a project might also be affected by reasons as site and weather conditions for traditional construction and factory conditions for modular construction.
In traditional construction methods, the quality control is greatly dependent on weather conditions and the skill and consistency of labor on the site. However the manufacturing process in modular construction can be quality controlled since it is consistent and is carried out in a protected and non-contaminated environment. The labor for modular building are also more skilled since most work is automated and the manufacturing is repetitive . We might thus conclude that the modular construction has greater potential to be of higher quality and produced in huger quantities in lesser time thus increasing the project productivity .
The cost of a project is an important determinant for stakeholders in the construction industry. This cost effectiveness of the project is dependent on various factors such as the time efficiency of the project, conditions on site, weather conditions, amount of materials and labor being used in the construction etc. A study  that compared the cost effects of both methods and found that modular construction is on average cheaper than conventional construction. This study did not take into account the operational costs of the building.
In modular construction, there is a significant return of investment as well as cost savings due to reasons such as lack of dependency on weather conditions or vandalism on site. Modular components are also transported efficiently in planned loads. In traditional construction, there are several loads of raw materials that are sourced from different places and this adds to the cost of the project. A study by Cartwright  emphasized that modular construction encountered significantly lesser costs because the design process is standardized and requires less time and engineering as compared to traditional design process that is more customizable.
A major influence on selection of modular process over traditional is the large number of deaths due to accidents in the construction industry. There are several factors that affect the safety on site but the chief being occupational hazards on site due to operation of machinery and equipment. A study by Klakegg  observed that the majority incidences of accidents occur on the site making off- site construction activities safer than on- site ones.
The construction work on site includes a lot of activities that threaten the safety of workers and stakeholders are constantly looking for more options to prevent the same. It has been found that because most processes of modularization occurs off-site in a controlled environment the incidences of fatalities and non-fatal injuries are greatly reduced. In traditional construction most or all processes that involve heavy machinery for excavation and installation take place on the site increasing the incidences of accidents. According to a study , the rate of accidents decrease by 80% by the use of modular methods of construction. We must however keep in mind that installation of modules on site require skillful handling of heavy machinery and there must be appropriate safety framework in place for modular construction as well .
Project complexity and associated Costs:
The complexity of a project can also determine the cost associated with its construction and may be a major determinant for project stakeholders who may choose traditional over modular methods. This is due to several factors such as availability of an experienced fabrication unit for manufacturing and the availability of skilled labor for proper assembly on site.
Modular construction can manufacture economical modules but will require the establishment of a quality fabrication unit. In traditional construction on the other hand, the process of acquiring permits and cheaper labor and materials are available, stakeholders may choose on-site construction over modular. For modular construction more skilled designers, suppliers and contractors are required and the lack of such skilled and experienced persons might be a constraint to using this method . Apart from field expertise a large amount of research and analysis is required for particularly complex design, manufacture and installation in modular construction as compared to on-site building. This will also affect the cost of the project .
The level of detail in planning that goes into the execution of a construction project will greatly determine the choice of the construction method. There might be varying differences between the two methods such as design, planning, estimation and costing etc. A study  established this difference such that in modular construction there is a difference of up to 37% from traditional construction methods.
In modular construction complex components have to be produced and assembled in the factory that makes the planning process and designing particularly complex. This requires additional input from workmen who have experience in manufacturing complex prefabricated components. Therefore, accurate planning with explicit scope and design details is required prior to the start of the project . The complexity of planning is less for traditional construction and a lot of project decisions are taken on-site based on the changing attributes of weather conditions, labour and project schedule.
The environmental performance of a construction project is a very important determinant to make an appropriate choice. Several studies have pointed out that semi or full prefabrication of components off-site led to significantly lesser embodied carbon and greenhouse gas emissions. However there are many determinant factors such as the distance from manufacturing plant to site and the subsequent increase in carbon emissions during transportation of modules.
The construction and demolition waste generated during traditional construction has been a valid environmental concern for all stakeholders in construction industry. Studies have found that the manufacture of prefabricated components in a plant will generate less waste than traditional construction . Whatever waste is generated in modular construction is also easier to dispose correctly in a way that doesn’t harm the environment . The components in prefabrication are easier to reuse and recycle because of the stringently controlled design and production as compared to traditional construction. In modular construction, entire modules may be dismantled and transported to another site for installation and individual components may also be detached and re-used. As compared to traditional construction, modular construction also produces less on-site dust and noise pollution as well as greenhouse gases .
‘How and When’ to choose one building method over the other
There has been growing awareness and more emphasis on construction projects that are economically, socially and environmentally sustainable. This clearly creates a question about which construction methods perform better in these areas. Our analysis of several factors related to a construction project show that:
- The design process for both methods are vastly different. Modular construction demands freezing the design before the manufacturing and assembly work of the home. In traditional construction this process is more sustained and fluid, allowing for last minute changes to design on –site. While this is an apparent advantage, it can also increase the risk factors associated with unplanned design modifications such as delays and increased project costs.
- It is important to derive a detailed cost estimate at the project feasibility stage, based on the design considerations and site conditions. For ex: If a manufacturing facility is situated very far away from the site and subsequent costs of transportation bring the project cost up considerably as compared to transporting raw materials for a traditional building.
- Increased innovation in the design of modular housing has led to an admirable range of design typologies such as ranch style, two storey, Cape Cod style and even green modular homes. However, traditional building still offers more variety when it comes to the aesthetics of design.
- In modular construction each module is a separate unit. This means it’s easier to add, remove or extend an existing module. It also makes the modular system scalable and provides the opportunity to reconfigure the modules easily in a different location. This is quite different from a traditional site-built home that might run into complications for extension and cannot be moved from the its original location.
- When it comes to comfort, a modular home company will undertake the task of developing the team that will assemble the entire house including the services such as plumbing and HVAC. Modular building also significantly bring down project time from 8-10 months to 90-120 days, while not compromising on project quality. So if you would like a faster return of investment and like to move in quickly into a new home, modular construction makes more sense that traditional stick-built homes.
Every building project comes with its own set of unique conditions and complications. Considering all these points, a detailed assessment of the development goals of the project, a comparative cost analysis and studying the site and market conditions will help choose the right method of construction for the project. Modular construction is found to be more effective that traditional construction in terms of environmental performance, higher project productivity and quality and lesser project costs.
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