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DfMA Falls Short for Modular Construction

The root cause of two common issues with modular buildings

The term Design for Manufacture and Assembly (DfMA) is widely used by modular suppliers to explain the difference between the pre-construction process for a modular and a traditional building. There is plenty of hard evidence that DfMA improves the cost, quality and efficiency of industrial manufacturing processes. But does that mean that using DfMA for modular manufacturing also solves the challenges of modular construction?

What is DfMA?

DfMA is the combination of two design methodologies. In the 70ies, Dr. Geoffrey Boothroyd, who had a history in the industry and was teaching at the University of Massachusetts, introduced Design for Manufacture (DfM), which is a method for the design of individual parts of an assembly. In the 80ies, Dr. Peter Dewhurst joined his team and together they developed Design for Assembly (DfA) which is how to assemble all the parts to make the final product. www.dfma.com

The core principle of DfM is to simplify the design of a product by reducing the number of constituent parts and by selecting the most cost effective materials and processes in their manufacture. In addition to that, DfA aims to minimize the number of operations and therefore reduce assembly time and cost of a product. Soon, both were combined to DfMA.

The use of DfMA in modular

DfMA as a term is widely used by the modular manufacturing industry to explain that the design of a building needs to take on board the particulars of the modular construction method. However, in most cases their definition of DfMA roughly narrows down to the dimensional limitations for transportation, the consequences of dispersed vertical load bearing structures, limiting the variation of modules and the need for stacked MEP risers.

The architects who design the buildings are usually not asked to look at manufacture or assembly because, other than for instance industrial designers, they have a lack of knowledge about these processes.

It is fair to say that today we merely see Design for Assembly (DfA), whereby Assembly in many cases is confined to the assembly of the modular scope within the building envelope. The knowledge about how this assembly takes place is currently proprietary to the modular supplier. This explains why their early involvement is so important.

From DfA to DfMA

Modular manufacturers roughly split in two categories; those who fit out complete pre-assembled steel cages and those who assemble modules from pre-assembled panels (floor, 4 walls, ceiling).

The majority of modular manufacturers belong to the first group. They fit out completed steel cages that they usually order from external steel manufacturers. When the steel cages arrive in their factory, the fit-out activities follow the traditional path of construction, using the same materials and methods. Hence, many modular manufacturers do not provide much more than construction under a roof. Interesting enough, just doing that already brings many advantages compared to a traditional construction site.

Once these manufacturers start to apply prefab sub-assemblies, tailored products, special machinery and methods to improve their manufacturing process, they make their move toward applying DfMA.

The second type of manufacturers assemble modules from pre-assembled panels and other sub-assembled elements. These manufacturers are more advanced. They have invested in substantial R&D to develop their building systems. Their factories clearly demonstrate a certain degree of automation and investment in assembly lines. DfMA is at the core of their business and they are in a position to monitor, test and optimize every step of their process.

Ground control, we have a problem…

There is no question that DfMA is a tool that has demonstrated tremendous value for industries around the world. Although several modular manufacturers have adopted the ground principles of DfMA, there are unfortunately a number of modular projects that face serious problems during assembly on site. This raises questions about the scope and implementation of their efforts.

To find an answer to those questions, let’s have a look at the two most occurring problems: Water damage and tolerance issues.

Water damage is in some cases the result of transportation when using improper protection. However, in most cases it is the result of damage to the waterproof membrane during handling and assembly of the modules on site. In many cases, the final installation is done by the main contractor, or a third party, and it appears that often they are not, nor have been made, aware of the vulnerabilities of the product they handle.

Tolerance problems are the second most common issue. Modular units have a very tight tolerance field of < 5mm (< 1/5 inch). Traditional construction uses tolerances up to 5cm (2 inches). Contractors are very skilled in resolving tolerance issues on site. For instance, if they have poured too much concrete in a foundation, which results in a higher first floor, they will take off some of the height of the upper floors in order not to exceed the approved building height. However, if they have to stack pre-manufactured volumetric modules with fixed dimensions, they can only solve the issue by lowering the foundation.

The water issue lays in the hands of the modular supplier. He needs to provide a fail proof product that can be handled during transport and in the harsh environment of a building site. Modular designers need to spend more time on site to understand the reality of construction. Also better training of workers on site needs to be provided by the manufacturer in combination with stricter supervision.

The tolerance issue can only be resolved by closer cooperation between the contractor and the modular supplier during the pre-construction phase. It does not only require education of the contractor but also training of the workers on site and much stricter quality control procedures during the traditional construction of critical interface points.

Combining manufacturing and construction

DfMA is a leading manufacturing tool and should be on everyone’s agenda when even thinking about modular construction. That said, it is not the final answer to the meticulous delivery of a modular building.

Any modular building, from a single home to a large high rise tower, requires an element of traditional construction. This could be as simple as a beam foundation or as complex as elevator cores and shear walls but in any case creates a complex interface between two different trades. DfMA is an industrial tool and therefor does not take into account the non-manufactured parts of the building that are in the hands of the contractor on site. As a result of that DfMA does not address the most critical element when volumetric modules and site conditions meet: Construction.

It would be too easy to assume that contractors fall in the Assembly category because they don’t assemble, they build. Contractors are dealing with other challenges and processes than manufacturers and it would be foolish to expect that they will suddenly change their routines for a new building method that currently covers only 3-5% of the market.

The success of the modular industry depends on their capability to work together with clients and local contractors to deliver great projects. Construction is an essential part of the delivery of a modular building and should be at the top of mind of any modular supplier during all stages of a project.

In my view, the modular industry needs to provide much more guidance and support to contractors in order to help them succeed. Because in the end it is not about modular suppliers or contractors but about happy clients that get better buildings delivered on budget and on time. That is the only thing that counts if we want to move the modular industry forward.

To underline the importance of the role of the contractor in the modular building process , I suggest that from now on we start using DfMCA; Design for Manufacture, Construction and Assembly. A constant reminder to everyone involved that this is not just a manufacturing process. Also a clear message to the contractors that we are doing something new that requires their involvement.

About the Author

Carel van Houte is a modular building expert with 15 years of experience in Europe and the USA. For citizenM hotels he created the revolutionary modular building system that changed the hotel industry.

Carel works as an independent adviser for developers and manufacturers of modular hotels, multifamily projects and student housing. carel@prolodge.nl

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