The economic and environmental benefits of modern methods of construction are a big factor in the dash to build new homes. But are there inherent fire safety issues which should lead us to pause for thought, asks Ron Alalouff?
Before discussing the fire performance aspects of Modern Methods of Construction (MMC), it is worth defining what we mean by the term. One of the best working definitions is from the NHBC Foundation which says:
“[MMC] is a wide term, embracing a range of offsite manufacturing and onsite techniques that provide alternatives to traditional house building. MMC ranges from whole homes being constructed from factory-built volumetric modules, through to the use of innovative techniques for laying concrete blockwork onsite.”
Image from NHBC Foundation research
According to the MMC Definition Framework by LHC, a local government provider of framework agreements for local authorities, social landlords and other public sector bodies, material genres can be defined as follows:
It goes on to define seven categories of MMC:
The main concerns about the fire performance of MMC include:
But others argue that MMC – especially their greater propensity to be manufactured at least to some extent off-site – can be produced under controlled factory conditions using the latest digital measuring and control technology. It’s said that quality control is far easier to achieve under such conditions than among all the variables on construction sites.
There has been a considerable amount of debate over the fire performance of MMC, although this has usually involved high profile fires in timber frame buildings under construction, rather than other types of MMC. Timber construction also tends to get lumped together, though in reality there are several types of timber products and construction methods with different fire performance characteristics. Cross-laminated timber (CLT) for example, comprises engineered structural panels made from gluing longitudinal and transverse layers, giving it the strength to be used for walls, roofs and floors – sometimes even in high-rise buildings.
“A key element when thinking about MMC construction is the approach to the building materials and how they interact with each other,” says Stuart Daws, Allianz Insurance’s Head of Loss Control Engineering, Technical. “For example, exposed combustible materials in a finished structure present quite a different fire risk to those fully encapsulated in non-combustible or fire resistant materials. This is where realistic and ‘real world’ test standards have a crucial part to play to ensure MMC materials and systems are fit for purpose. It’s an area that needs further scrutiny and development, alongside regulation, so that safer buildings can be constructed and keep pace with the ever-increasing speed of innovation in this area.”
Commenting on the potential fire performance of MMC, Niall Rowan, CEO of the Association for Specialist Fire Protection, says: “In that MMC are usually made from low density combustible materials, there is an ‘inherent’ hazard. However, the petrol in the tank of your car is highly combustible and so also an ‘inherent’ hazard, but we have developed ways and means of mitigating that hazard.
“For MMC, there are methods of protecting the materials used such as encapsulation. The important thing is that these are applied/installed correctly, and that compartmentation and firestopping is tightly controlled, because buildings built using MMC processes are less resilient against poor workmanship than traditional methods of construction. In addition, building owners should undertake regular inspection of passive measures and tenants need to be aware of their responsibilities not to compromise compartmentation by, for example, DIY works. Both groups need to be aware of the potential hazards.”
One of the hurdles to constructing safe buildings using MMC is that it is often difficult to relate current building regulations and Approved Documents to innovative products and techniques. This was first highlighted by Dame Judith Hackitt’s Independent Review of Building Regulations and Fire Safety. The baton was then taken up by the Commons select committee for Housing, Communities and Local Government, which said in its report on MMC:
“The current suite of Approved Documents is confusing and difficult to comply with. It is particularly difficult for homebuilders that use MMC to apply the regulations to their developments. This could result in compromised safety standards in MMC buildings. The consultation on the building and fire safety system is welcome but does not consider specific guidance for MMC builders to help them comply with current regulations.”
The select committee recommended that the Government should urgently set out a clear plan for the review of the whole suite of Approved Documents, including a timeline for implementation. The review should consider how the Approved Documents relate to MMC buildings and where relevant, provide additional guidance on how homebuilders might reach the required standards.
In its evidence to the select committee, the Fire Sector Federation said that while properly using MMC can offer considerable economic and social benefits, “such forms of construction open the potential for unseen and uncontrolled rapid fire spread, through cavities and beyond designated fire compartments.” It said the key to controlling fire in MMC buildings starts with “clarity around the actual definition and control of the combustibility of materials, limiting fire spread by emphasising the effectiveness required in fire barriers and construction separation, and ensuring during construction these detailed requirements are applied, not skimped upon or ignored”. It also repeated concerns that current building regulations and guidance are not sufficiently detailed to ensure safe use of MMC, with materials such as plastic potentially creating “pathways for external fires to enter structures, or fire barriers and seals [being] rendered ineffective by surrounding materials”.
Also giving evidence to the select committee, the Association of British Insurers said:
“MMC products often incorporate lightweight combustible materials such as wood, polystyrene and recycled materials, which have the potential to increase the risk of fire spread… Hidden cavities and voids caused by bad practice during the installation phase can also enable the spread of flame, smoke and toxic gases, causing harm to any inhabitants within the building.”
In its consultation Building a Safer Future, the Government proposed a “golden thread” of digital information for all multi-occupied residential buildings of 18 metres or more, where there is more use of digital technology and digital information complies with Building Information Modelling (BIM) standards.
The Government has reiterated its commitment to a full technical review of Approved Document B, to ensure it reflects the latest innovations in construction technology. It will also set out its proposals to deliver the recommendations from the Hackitt Review on ensuring that Approved Documents provide a more streamlined, holistic view of guidance that is clearer and more user friendly, while keeping the right level of technical detail.
As part of the full technical review of Approved Document B, the Ministry of Housing, Communities and Local Government (MHCLG) has commissioned research that will identify knowledge gaps and areas where additional guidance may be required to account for modern methods of construction and materials in common buildings.
“All homes, including those made using Modern Methods of Construction, must meet building regulations and fire safety standards,” said an MHCLG spokesperson. “The government has worked with various assurance and warranty providers to improve the quality and standard of MMC homes.”
The Government has also created a housing specific MMC working group to look at barriers to assurance, insurance and finance for homes manufactured using MMC.
Some of the fire safety issues inherent in MMC may also be addressed by the Government’s proposals for a reformed building safety system. These include the setting up of the Building Safety Regulator to:
Other government proposals which may impact MMC are the setting up of a new national construction products regulator and a new construction products standards committee. The latter will comprise technical experts and academics to advise whether voluntary industry standards for construction products should become UK regulatory standards. The committee will also provide advice on the conformity assessment process and product test standards.
There’s no doubting the desire on the part of government to build more homes, with £2.5bn invested in support of small and medium sized builders, custom builders, and innovators with the aim of delivering at least 52,000 homes by 2022/23. And it’s likely that a growing proportion of these homes will be built using MMC, given their potentially superior performance in areas such as build quality, energy efficiency and reduced environmental impact. And in the wake of the Hackitt report, the MHCLG is at least talking the talk about specifically addressing gaps in knowledge and guidance about MMC in its technical review of Approved Document B.
Whether it will walk the walk by producing thoroughly revised guidance fit for these innovative ways of construction, and whether it will provide an appropriate framework for product and installation standards to remove the potential fire risks, remains to be seen.
Given recent examples of fires involving modular and lightweight timber frame, the government could easily include multi-occupied residential buildings built in this type of construction, in the scope of the new ‘Building Safety Regulations’. This would mean tighter controls being imposed at design and planning stage and make the principal designer and principal contractor accountable if the place burns down to the ground. In addition all existing MMC residential would be subject to an enhanced management system, which would include a ‘safety case’ approach. This would offer residents some much needed confidence in their building and its resilience to fire.
The construction sector regularly fails to correctly fire stop traditional build systems, or install cavity barriers. As these are much more critical for an MMC building, clients should re-think this choice until specialist companies arise with expertise in this form of construction. Equally, clients should keep good records where these techniques have been used, as repairs and refurbishment work needs to be done with more care to avoid fires, such as during hot work.