Prefabricated / Modular Method of Construction

Dean Suttling

March 25th, 2022
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Construction is the largest user of materials in the UK and the most significant waste stream with historical data demonstrating that of the 189 million tonnes of waste produced by the UK, nearly three-quarters is created by the construction industry, with 5 million tonnes sent to landfill. The UK Government issued its ‘Resources and Waste Strategy (2018)’ to eliminate avoidable waste of all kinds by 2050 in England to tackle this.

In terms of construction, traditional methods have involved delivering the raw materials to the site and then various trades connecting, installing, and jointing together these basic materials to construct the permanent works.

However, putting materials together off-site ready to transport and connect to reduce waste and become more efficient, is not new. Still, to succeed, modular construction depends on the site conditions, the type of project, access, required design and the project-specific constraints.

With advances in technology, however, modular – which involves the off-site construction of the parts or sections for fast and efficient construction onsite – is becoming increasingly popular in the drive to be more efficient and effective in delivering projects and the drive to reduce material wastage.

Modular Construction

This type of construction favours the rapid construction of temporary buildings where the design is uniform and can be manufactured and quickly finished on site. Initially built for function instead of aesthetically pleasing, they were popular in the late 1940s after WW2 when the UK needed low cost and immediate housing needs and government-owned buildings; for example, in the four years after 1945, the UK constructed 156,000 fabricated homes.

Many of these structures, whose original purpose was to provide function on a ‘temporary’ basis, outlived their design life. Therefore, the vision of modular builds became one of the dilapidated buildings. This cast something of a shadow over modular, and they fell out of favour for some time. However, putting aesthetics to one side, the UK Government needs to construct 300,000 homes each year to hit housing targets, and the current build rate is approximately 200,000 per year, of which about 15,000 are modular. Therefore the rapid build modular and prefabricated market can play an essential part in meeting these targets as we advance coupled with the 2050 net-zero targets.

In terms of examples of modular building construction and the uses for them, these also include:

  • Temporary school classrooms
  • Construction site accommodation
  • Emergency accommodation
  • Buildings for practical use have hotels, offices, healthcare buildings and manufacturing houses.
  • Residential Housing

Prefabricated

This method involves manufacturing components off-site in a factory before being transported and connected on site. Different to modular in that you still need to construct the parts together, so for example, modular could mean the plumbing, electric is already built into the units meaning that simple connection onsite before finishes are applied. This is known as volumetric modular construction. Prefabrication is more about the panels associated, e.g., walls, floors and roofing structures assembled on site before the first and second fix works are undertaken.

Advantages

In terms of either prefabricated or modular construction, the key advantage is the speed of construction, including the manufacture and supply time. Through this reduction in time, there are savings in the management time or initial costs onsite, which, coupled with the speed and efficiency of factory manufacture, is likely to be considerably more cost-effective than constructing directly on site.

If you consider the repetitive nature of manufacture coupled with the ability to order materials in high volume, further reducing the costs of construction can be as high as 15-20%, with wastage also reduced through reuse.

Notwithstanding the immediate cost impact, there are other factors such as the environmental impact, where the speed of onsite assembly means reduced periods for noise and waste. As well as this, a minor site operation can be used as there is no need to have numerous materials laid down and storage areas for plant and equipment.

Due to the manufacturing process, it is possible to achieve improved build quality over that which could be built onsite. This means that We can achieve greater precision with tighter tolerances leading to a better finish than traditionally performed. If the technological advancement in the production state also includes BIM modelling, errors, clashes and assembly issues can be identified and removed before taking to the site. However, there is a balance on the business case regarding investing in modelling technology versus what could be temporary or semi-permanent buildings. However, from a different perspective, the buildings can be easily adapted and extendable, and through basic modelling, you will be able to demonstrate the adaptability of the design.

Another key advantage is the reduced amount of people, plant, and machinery interfaces onsite, reducing the number of workplace injuries. If you think of the construction industry and the onsite risks associated with working at height and falls, reducing or removing these risks is advantageous to safety-conscious contractors and clients alike.

Disadvantages

Regarding disadvantages, the obvious one is the restricted flexibility, as with the speed of mass manufacturing comes some rigidity in the design. Similarly, the overall look and feel can be poorer than more traditional options available for a finish. The use of these build types is usually practicality or function over style. Similarly, they may be designed and constructed with a maximum budget per unit etc. Likewise, because of this, the resale value can be very low; for this reason, coupled with the lack of mobility of the units means, the costs associated with deconstruction and removal makes the residual value of the buildings neutral or nil.

Suppose the build is part onsite and part modular or prefabricated. In that case, the differences in tolerances when fixing the two together can lead to constructability issues, which can lead to delays and disruption on site. The worst-case scenario here is the remanufacturing of the components or making amendments to the already constructed permanent works leading to possible defects. However, conversely, you can counteract this with BIM, but investment on this scale will only depend on the value and type of project where the risk is likely to remain.

Also, the prefabricated and modular building industry is primarily unregulated for temporary buildings, presumably due to the product’s low cost and temporary nature. However, suppose standardisation is possible in terms of design. In that case, you can improve standards, but clearly, a balance is to be struck between the value for money and longevity versus investment in the standard of the build.

Hidden Costs

From a review of the above, the onsite savings in labour and plant plus the associated savings in initial costs are undoubtedly appealing, notwithstanding the reduced health and safety risks. However, there remain other costs to consider when staking up the business case, and these are:

  • Set Up Costs – The factory setup cost can be steep with full-time staff, facility costs, and general running costs. Also, unless an established factory can make the components, the setup costs can be high compared to the margin forecast making the business proposition seem unappealing unless substantial orders are coming through.
  • Transportation – with the parts or panels being considerably larger as they are constructed off-site and not in-situ, their transportation is slow and costly, which, once delivered, could require more expensive craneage and handling fees.
  • Design Development Fees – the coordination between architects, engineers and the fabricators will need to be concentrated due to the tighter tolerances involved in the manufacture and the need to make this fit on site. As a result, the fees for managing this could be higher.

Advances in Technology

These can be in two different types of modular buildings: permanent or temporary in terms of the design solution. In either case, the improvement in BIM and the ability to use digital planning and coordinate between all trades and gains in fire and building safety can mean that you can achieve regulatory compliance for permanent solutions mostly in advance of the final build.

As a result of the benefits of constructing in factory conditions, the units are generally better insulated and more airtight than those created in-situ on site. This means better heating and reduced energy consumption and therefore running costs which could also be reduced by as much as 20%.

Examples in Practice

Network Rail’s Strategy has long set a vision for consistent, high quality and standardised stations and stations facilities and historically hampered by the solutions being isolated in nature instead of a programme of works meaning that they did not realise the full savings. To tackle this issue, Network Rail created a rationalised product component library to establish long-term efficiencies that are low carbon and durable, maintainable, safe, and fit for purpose.

Fast forward to only last year, and Network Rail launched an enquiry across architects, engineers, and designers from across the globe as to how they could improve the travel experience, which attracted entries from 34 countries. The winner was a modular station design that they could use in several locations. With minimal parts, the onsite build would be efficient and safer. The buildings themselves generate renewable energy that would power most of the station’s energy needs, which supported Network Rail’s 2050 carbon-neutral aspirations.

Photo by jesse orrico on Unsplash

About Dean Suttling

A member of the Royal Institution of Chartered Surveyors, Dean has twenty years of experience in commercial management and quantity surveying, undertaking roles for contractors, clients, and consultants.

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