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Modern Methods of Construction (MMC) – Time, Cost, Quality, and The Building Safety Act

14 Nov 2023

Kieran Bradley

Kieran Bradley


Kieran Bradley, Director of Architecture, delves into the dynamic landscape of Modern Methods of Construction (MMC), a concept that, while over a decade old, its interpretation and applications are constantly evolving and changing, drawing lessons from each individual scheme. He sheds light on the shift away from conventional building practices, highlighting the growing emphasis on alternative, innovative construction techniques and explores the benefits of offsite factory-based construction methods, which promise not only to expedite the building process but also to enhance quality control.

Read more in our 4Q 2023 Market Intelligence Report

The 1920s saw the first large-scale adoption of MMC using pre-cast concrete in buildings, bridges and other structures. It wasn’t until the 1970s when volumetric modules began to enter the market. This process suited construction with a large element of repetition: for example, hotel rooms and student accommodation. These buildings were compatible with the technology due to their ‘drag and drop’ design, acting in essence like ‘largescale Lego’ placed on top of transfer slabs, creating more versatile spaces below for amenity spaces.

MMC generally receives positive industry feedback and our survey confirmed this, with 78% of respondents saying there was a quality benefit to MMC, including 92% of contractors. However, there is an inherent danger for companies that dedicate substantial resource to the practice without fully considering the challenges of deploying it in schemes when it is not the most suited option, which can ultimately lead to cost and programme issues.

Many of the largest fabricators within this industry are surviving by filling their production lines with diverse forms of MMC production, using a range of standardised elements that can plug any gaps in the production line, should the MMC orderbook slow down.

The experience of working with MMC has widely penetrated the UK consultancy and contracting sector. Our survey showed that 85% of participants have recently utilised a Modern Method of Construction within a project - and that 80% of these expect to see an increase in MMC utilisation within construction over the next five years.

How is MMC working in practice today?

Sectors like education, prisons, and healthcare have all made significant strides in the use of MMC. This is helped in no small part by the UK government throwing substantial funding behind the practice in each of these areas. It is evidenced by the MMC1 programme for development of schools, while the Ministry of Justice (MoJ) has embarked on a huge £1 billion prisons programme with a blueprint design for four new ‘megaprisons’ that each use MMC to meet a strict delivery timeline.

Similarly, the Department for Education (DfE) has set out and maintains its own set of design practices for its school regeneration programme. Each new school it undertakes must include adherence to principles such as a linear design, standardised wall to floor ratios and stacking elements, which make it incredibly easy to add or remove classrooms at will. This helps to meet one the biggest challenges in the sector – space and teaching sizes, with a growing population and increasingly diverse needs.

A note of caution, however, has recently been exercised in the industry with the RAAC crisis, with three modular schools built by Caledonian Modular having closed over fears that the buildings were structurally unsafe. Such evidence points to the need to consistently review and refine modular practices to ensure they are best suited to their intended environment.

Where do the opportunities lie?

The constant pressure of the housing crisis makes MMC an attractive option to a number of stakeholders in the residential sector. Offsite construction is proving particularly effective within the build-to-rent and student accommodation spheres, where the requirements sit on a consistent pattern year after year with a new influx of renters or students.

The government has a vested interest in MMC given its target of building 300,000 new homes each year. Again, social and more affordable housing sits in a sweet spot for MMC for the reasons already detailed, yet residential housing presents a trickier problem for housebuilders. This is due to:

Mixed-use schemes: the growth and emergence of this sector means a mixture of housing types are required and furthermore need to be considered not just in isolation, but how they will interact with all of the other elements on the same site - i.e. retail, social, or care facilities.

High-rise and tall, densely populated homes: where new land is becoming increasingly hard to find, contractors are forced to repurpose inner city buildings, which don’t always fit to the standardised spare requirements that MMC needs for it to be truly effective.

What are the programme benefits from using MMC?

The key benefits centre around consistency of quality and a reduction in delivery time on site, both of which have further budget and sustainability benefits.

Time saving

Simply put, using MMC reduces the time needed to deliver work on site. A shorter overall programme results in a corresponding cost savings with site based amenities and mass of staff numbers.

However, to allow orders to be placed with off-site manufacturing companies providing MMC systems, the design and procurement programme needs to pulled forward more than a traditional construction route to ensure full detailed design prior to production commencing in the factory. With the new Building Safety Act Gateway 2 having come into effect in October 2023, consideration around procurement and approvals programming will also need to be factored in. From our research, 80% of contractors have reported they see Gateway 2 as either ‘affecting’ or ‘maybe affecting’ programmes and procurement for MMC builds.

Once on site, MMC schemes are delivered at pace with accuracy. This allows for building programmes critical paths to be drastically reduced creating a watertight building sooner, allowing for internal works and fit-outs to commence.

When compared to traditional construction, MMC methods like modular can save contractors time and money, especially when they can lessen reliance on labourers with specialised skillsets, like bricklayers, who are currently in short supply.

As architects, we must take many things into account during the design stages to allow for alternative solutions during the construction stages. For example, a 20-storey brick façade could be installed as traditional bricks, a brick slip system, or a panelised brick approach. Where design consideration around scaffolding versus mask climbers is required, a panelised approach could involve the use spider cranes and mitigate the need for any external temporary access and repair works following mask climbers or scaffolding being removed.

Both with MMC and the Building Safety Act Gateway 2, early engagement with contractors is critical to ensure projects remain on programme and are delivered efficiently.

Quality assurance

Revisiting the example of a high-rise building, utilising panelised façade construction methods manufactured in a controlled internal environment allows for consistency in build quality throughout the production. This leaves much less room for human or environmental error such as working at height on a cold winter’s day, meaning a higher quality product with much less risk factored in.

In certain sectors, the development of easily replicable modular designs is a huge advantage. For example, a three-wing prison will be designed to be the most efficient shape and layout for its usage – and once designed it can be rolled out multiple times for different prisons. Meanwhile, for hotels, room units are often produced offsite and slotted together – again reflecting the ‘Big Lego’ metaphor.

It’s also important to remember that modular may be a whole building or element like a hotel room block, but it may be other elements too. For example, flexibility and adaptability means it’s not one or all, and it is perfectly possible to have modular elements within a traditional build, such as pre-made services and ductwork runs or panels.

The ability to reuse materials and minimise wastage through manufacturing is an additional advantage of the MMC's uniformity and quality. In theory, many materials can be reused in some capacity, since they have components that are made to be easily removed, disassembled, and recycled.

Are there any downsides to MMC?

In addition to the increased upfront costs (32%), and programming issues (24%), our market research has found that future flexibility and design change (31%) to be the biggest challenges of using MMC. Interestingly, design compliance (13%) and quality of the finished article (0%) weren’t seen as so challenging.

Not all jobs are suited for modular construction. In some instances, they can prove to be too complicated, or the site might just be too small to use cranes. In other cases, it can be down to the actual scheme. For example, there are not as many MMC options for retrofit for the most part due to the completely bespoke solutions needed for such schemes.

A significant disadvantage to MMC is the higher upfront cost required. The need to have immediate design approvals, before putting in factory orders, brings the entire programme and funding forward within the programme. Additionally, once this design is put into order, it doesn’t allow much flexibility for change without attracting significant cost.

While the money saving overall comes from the overall construction programme, the short-term impact means contractors having to put in an upfront scaled cost at the outset.

In simple terms, some contractors don’t like – or simply can’t – do this, particularly with materials costs still being fairly volatile in the current market. We are already seeing the potential impact of this financial burden across the market with the closure of L&G’s modular housing factory, as well as modular housebuilder Ilke Homes also having collapsed.

Perhaps the most alarming issue with modular construction has been highlighted in the Caledonian Modular story, where the repetition has actually led the contractor to repeat the same design flaw.

Where will MMC go next?

This is one of the golden questions in the sector – and it hinges on what is going well, or not so well right now.

That’s why our survey asked what one thing people would change to improve the uptake of MMC, which returned three key themes:

Education – both in terms of client understanding, appropriate use of MMC, and the balance of capital cost against other benefits like site time reduction, quality of finish and reduced risk.

Early integration – making sure that positive engagement early on works with longer lead times.

Flexibility and adaptability – to improve connectivity with other elements like MEP, aid futureproofing retrofit and adaptation, and within procurement processes too.

From a blue-sky thinking perspective, there are already companies 3D printing elements of buildings. Could this expand to a point where an entire building, complete with walls, could contain services and finishes? And, installed robotically on site?

The biggest immediate challenge regarding MMC would be the changes in the Building Safety Act and flexibility around design. The desire to make as few changes as possible during manufacturing and construction is a commonality between the new Building Safety Act regulations and MMC practices, but there will be questions about how Gateway 2 will have an impact, where confirmation is required, and how the requirements of the Building Regulations are met before works can start.

MMC has many advantages, along with many challenges – given the recent closure of several big name MMC suppliers, the question regarding mass market capacity still needs to be answered.