Expert Q&A: modular home-building

According to a report published last year (October 2022) by Make UK, factory-built precision-engineered homes could help to both decarbonise the construction sector and solve Britain’s growing housing crisis. The Engineer spoke to a group of experts from across the sector about the potential of off-site construction for new home-building

Meet the experts

Steve Cole,director of Make UK Modular at Make UK

Gill Kelleher, head of energy & housing data insights, BRE Group

Timothy Snelson, director and structural engineer, Arup

Jonny Reid, technical specialist, assembly systems, Manufacturing Technology Centre

Why should we be considering off-site construction for new home-building?

Steve Cole: Put simply because it’s greener, better, and faster. UK housing is in crisis. For more than 40 years we just haven’t built the homes we need leading to increasingly unaffordable rents and house prices. The construction labour force is old, shrinking by more than 120,000 in the last 3 years, and the sector faces robust new low carbon targets.

Factory engineering means modular homes can be built to consistently high standards, lower cost at greater speed, and delivered to sites with hugely reduced disruption. They create jobs at the factories which can be located where they are needed, and houses and apartments delivered to where homes are needed.

Gill Kelleher: By far the biggest reason is the anticipated productivity gains in addition to the improvements in building safety and design, which will enable us to construct greener, safer, and healthier homes. Furthermore, with modular construction we can build at pace and at scale without compromising on quality or cost.

Additionally, we are in a climate emergency and by adopting best practice principles from other sectors, such as the aerospace and automotive sectors, we can embed advanced quality management processes to optimise system efficiency without compromising on quality. For the UK to fulfil its net zero ambitions, this will make it more straightforward to track and limit embodied carbon, by utilising the controlled environment that manufacturing-led construction brings. 

Timothy Snelson: With the housing scarcity nationwide, an energy crisis and the UK government’s pledge to build 300,000 homes annually there is a real need to move away from traditional on-site construction. Off-site construction, more specifically modular homes produced through Modern Methods of Construction (MMC), present an appealing alternative to traditional construction. They are up to 50 per cent faster to produce than traditional homes and often cheaper to heat - the average UK home costs double to heat than a modular home.

What are the environmental benefits?

SC: A study by Cambridge and Edinburgh Napier universities found a modular tower built by Vision Modular Systems had 41-45 per cent less whole life embodied carbon than traditional build. Modular homes, such as those produced by TopHat, can be built with up to up to 82 per cent less whole-life embodied carbon.

In an era of rocketing fuel prices, modular offers significant gains in energy efficiency. All Legal and General Modular’s new homes are EPC A (currently only two per cent of new homes nationally are in this category) while ilke Homes recently launched a Zero Bills housing system in partnership with Octopus Energy.

Jonny Reid: At the MTC, we understand there are numerous benefits offered by off-site construction, or Modern Methods of Construction (It is important to recognise that the transformation of the housing sector must consider the on-site activities and not just those migrated off-site).

These include key factors such as reduced waste, improved productivity and faster delivery. All of these contribute to overall emissions reductions. By leveraging manufacturing-based principles for managing materials supply and use, in tandem with Design for Manufacture and Assembly principles, it is possible to develop solutions which reduce the volume of traditional construction materials in the short term, and evolutions of these that replace them longer term with more sustainable feed-stock materials.

GK: Modular construction can make it easier to construct homes and buildings which utilise less carbon throughout their lifetime. Off-site construction can also help close the performance gap by designing buildings that go above minimum energy performance standards which negate the need to retrofit them in the future. This is important with nearly half of UK homes not meeting current energy efficiency standards which are essential for our climate obligations.

For example, a fabric first approach optimises the fabric of building – such as insulation, roofing, walls, floors - which reduces heating demand. This lowers fuel bills dramatically and, more importantly, reduces the demand for fossil fuels.

What are some of the key technologies involved?

TS: Examples typically include an all-electric approach. Air source heat pumps are common with some manufacturers fitting photovoltaic solar panels as standard.  There are also manufacturers providing battery storage and even products that offer zero bills.

These technologies all rely on having highly-energy efficient walls, roofs and windows, to minimise the energy demand from heat-losses through the fabric. So ‘fabric-first’ design approaches will typically result in lots of wall insulation for low u-values and low airtightness to minimise leakage. These highly insulated buildings are great for reducing heating in winter, but care must be taken in the design to mitigate summer over-heating.

JR: There are several fields of technology to be considered in this transformation. There are those that relate directly to the products developed and the processes used for their creation, and there are key enabling technologies which are required to underpin their robust delivery and control.

In our role as lead partner in the Construction Innovation Hub we’re supporting our industry partners as they develop innovative solutions such as laser cut reinforcement (LCR) developed by Metlase, which can improve repeatability and quality and reduce installation time, and prefabricated roof cassettes and partition walls which can offer better quality, reduce waste and increase safety onsite. These are demonstrated at the Hub’s physical testbed ‘sandpits’.

At the MTC we believe the critical approach needed is to plan the manufacturing processes and methods such that they will appropriate for a manual-intensive low volume approach, and be compatible with increments of manufacturing facility investment, up to automation and robotics.

Where are the opportunities for the UK?

SC: Make UK Modular members are on track to deliver 10,000 new homes a year by 2025 with an ambition to deliver 30,000 by 2030. This would be a step change in UK housebuilding. With a Compound Annual Growth Rate (CAGR) of 41.59 per cent over the next four years this is not a pipe dream but a real possibility.

British modular producers have the capacity to be world leaders in this field. They develop some of the best modular on the market and there is real potential for exporting designs and technology. Britain is world leading in exporting design, engineering, and construction management services. There is no reason why modular should not be part of this.

TS: In the next fifteen years, it is anticipated that construction will lose approximately 500,000 workers, due to an ageing population and a lack of skilled labour entering the profession. Off-site construction workforces can offset this as MMC does not require conventional construction expertise, while overcoming an obstacle to increasing housing supply.

Modular homes can be deconstructed and moved to other sites, so the UK housing supply shortages could be mitigated with temporary housing installed on ‘meanwhile’ sites that are awaiting development, such as Arup’s Ebury Estate pop-up units. 

Home-suppliers can grow a more circular economy service with low-carbon technology through the life of the home, by supplying equipment upgrades or using leasing contracts.

GK: The biggest opportunity for the UK is to significantly ramp up housebuilding efforts which have been falling below the 300,000 a year target for quite some time.

We are currently suffering the consequences of living with old, poorly insulated, and carbon intensive buildings which result in high energy bills, exacerbate energy insecurity, and rack up demand for fossil fuels. When constructing new homes and buildings we must bear this in mind and ensure they are constructed for future generations and with adequate insulation and low-carbon heating technologies. Poorly insulated homes are currently costing the NHS £800 million a year, as revealed in our report on the Cost of Poor Housing, so it is crucial to address this moving forward.

By seamlessly integrating smart technologies into buildings, modular construction can help us accelerate this transition. It also brings with it a golden opportunity to upskill, or reskill, the construction industry. Green jobs will be key for the future of the construction sector and the wider UK economy, as carbon intensive jobs become redundant.

JR: The UK has a strong track record in manufacturing sectors, so there is no reason why we can’t bring these competencies to bear in the housing sector. We already have some fantastic MMC/modular housing providers in the UK but have yet to reach the scale of manufacturing needed to satisfy the total market.

With such demands and value of pipeline that the UK offers, we cannot ignore the potential for overseas competition to seek an export opportunity into our market, but I am confident the UK’s own supply chain could be scaled to match demands. One area of opportunity that should not be overlooked is the total emissions footprint of domestic versus imported MMC houses, and the consequential impact on our trade (im)balance in this sector. Rather than viewing these factors as a vicious circle, we should consider this a golden opportunity to support and enable the transformative change required within this sector and reap the benefits of a significant scale-up for the nation and economy.