Permanent Stacked Modular Buildings are being constructed as high-rise towers. Modular has become a familiar Modern Method of Construction (MMC) in which volumetric units of pre-finished room sized accommodation are stacked by tower crane around lift and stair cores. Often the cores are insitu reinforced concrete, and a wide range of Modular systems are available from a growing number of manufacturers.

It is important to anticipate how different Modular buildings address fire risk. A low-rise example was provided by the fire on 27 July 2020 which completely destroyed the Moorfield Hotel, at Brae in Shetland. This was a 100 room Hotel from which fire escape was direct and simultaneous. It had been manufactured in Northern Ireland and shipped by sea, using a system of Structurally Insulated Panels. These SIPs were timber boards facing a core of combustible foam insulation. It was unusual for a Permanent Stacked Modular Building to be made of such SIPs. The Fire and Rescue Service were unable to control the fire when it got into the cavities between modules and within the SIPs. In such a situation it was considered a successful operation to let the fire burn out the safely and speedily evacuated property.

Writing before the Moorfield Hotel fire in 2019, this type of MMC was called Category 1 by Mark Farmer of Cast Consultancy and defined as “pre-manufactured 3D primary structural systems”. [1] The Modular approach has been adopted by Housing Associations and Local Authority Developers for sale and rent, Student Hostel Operators, Private Rental Landlords, and many Hoteliers, all looking to position themselves in competitive markets. Some of the larger Home Builders and Main Contractors are getting into Modular. Architectural variation is as achievable as brand identity in Modular buildings, with financial arrangements to match.

Permanent Stacked Modular Buildings have diversified from the Temporary Modular Building sector that continues to provide expansion accommodation for the healthcare and education sectors, or site offices for construction projects. While MMC is a particular phrase in the UK based in Government policy, there is international effort to improve “offsite” manufacturing, delivery and on site installation. Standards are beginning to be developed at this frontier of knowledge.

Modules can be open-sided for stacking to achieve larger room sizes than the limitations on width consequential on road delivery, or on weight consequential on crane lifting for placement in the stack. The single widths of bedrooms with the bathroom, shower and WC adjacent to the entrance door and shared service risers off the access corridor suit Modular in Hotel and Hostel design. Adjacent rooms in Apartment buildings can have adjoining doors between Modules. Many residential or institutional floor plans can be “Modularised”, with their bathroom, shower and WC “Podularised” within.

For specialist consultants in planning applications this means giving architectural expression to the stacking of Modules and Pods, which are often drawn in three dimensional Building Information Models as manufacturer’s systems are favoured in contract tenders. Those systems are proprietary and vary considerably as more Modular manufacturers establish themselves with novice or repeating clients, innovate and diversify. There are thin “upcrete” cast concrete Modules, Steel Modules with and without loadbearing infill walls and floors, Timber Frame and Cross Laminated Timber Modules.

With such architectural expression and technical variation it can be difficult to know exactly how the Modular system has been designed and manufactured to satisfy the 2010 Building Regulations. Modular manufacturers may also be reluctant to reveal their system to perceived competitors, with much of what is manufactured not being patentable, but more a state-of-the-art question. Specialist Third Party accreditation and warranty schemes have established themselves to better understand Category 1 MMC for landlords and buyers alike.

To assist insurance providers the Fire Protection Association’s RISCAuthority has developed IQ8 Building System Questionnaire: Permanent Stacked Modular Buildings – Version 1.0. [2] This higher-level questionnaire focusses on the perceived challenges of Modular Building methods in respect of compartmentation and repairability, to assess the insurance perils of fire and water exposure. While it is part of the insurance focused IQ series developed by RISCAuthority, IQ8 is made freely available to anyone interested in Permanent Stacked Modular Buildings, such as Fire and Rescue Services or Building Control authorities.

For those wishing to ask lower-level questions about particular Modular systems RISCAuthority has also developed a Permanent Stacked Modular Buildings: Technical Checklist for England – Issue 01. [3] This corresponds to the higher-level IQ8 questions in Section 3. But is currently limited to England. It follows the alphanumeric of the Functional Requirements of Schedule 1. of the 2010 Building Regulations [4] as these provide the legal requirements in the statutory guidance of the Approved Documents [5].

It is expected that over time this technical exploration will further develop into a useful guide to the issues involved in Permanent Stacked Modular Buildings as they affect the insurability of the property additional to the requirement for Life Safety in the 2010 Building Regulations. It is also expected that versions of the Technical Checklist may be correlated with the Scottish, Welsh and Northern Ireland functional requirements and statutory guidance. But the effort had to start somewhere and most Permanent Stacked Modular Buildings are being built in England.

An urban high-rise Permanent Stacked Modular Building with a stay-put policy for phased escape predicated on compartmentation, manufactured to a proprietary system, though necessarily involving cavities between Modules in the compartmentation of floors and walls, would be quite a different fire scenario to that at the remote Moorfield Hotel. No-one wants that to become reality. It would destroy the Permanent Stacked Modular Building business.

The 2010 Building Regulations require Part B Fire Safety in England achieves Life Safety, but how will the Fire and Rescue Services fight a cavity fire in urban high-rise Permanent Stacked Modular Buildings?

Will the asset be a total loss, and what would that mean for neighbouring buildings?

How can it be demonstrated that the “offsite” manufactured Module stack was installed on site as-tested to achieve compartmentation?

IQ8 and the associated Technical Checklist will be updated over time, and RISCAuthority invites suggestions and criticism so that iterations may be improved. Please email Ian Abley, Principal Consultant, RISCAuthority – iabley@thefpa.co.uk. RISCAuthority published the Cladding Compliance Toolkit with a Flowchart for the devolved administrations of the UK. [6] These relate to the external cladding of Permanent Stacked Modular Buildings, where external cavity construction interfaces with the internal cavities of a Modular system. This can be hard to visualise, and other free online tools are anticipated, including drawings and models.

By asking better questions in the design of Permanent Stacked Modular Buildings there will be better answers to the legal requirement for Life Safety and the insurable risks in the “offsite” manufacturing, delivery and on site installation of Category 1 MMC assets.