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CONSTRUCTION METHODS MODULAR
Modular construction is touted as the future of the building industry, but while the sector is rapidly growing
in some areas, there are still obstacles to overcome. Alex Hyams of Alinea, Ed McCann of Expedition
Engineering and Hugh Ferguson assess the pros and cons of volumetric modular offsite construction
01 / INTRODUCTION
Is modular construction the future shows the way technology is Figure 1: Gartner hype cycle, showing a technology’s journey to
for the UK building industry as its adopted, with the “peak of inflated mainstream acceptance
supporters have long maintained, expectations” followed by the
or is it a hopeless effort to translate “trough of disillusionment” (see
factory techniques into an figure 1). The 2016 Farmer review VISIBILITY
unsuitable industry? The question put modular in the spotlight
has divided opinion since the again as part of the solution to Peak of inflated expectations
benefits of modular were hyped up the building industry’s ills. So is
20 years ago. modular now climbing Gartner’s
In the wake of the 1998 Egan “slope of enlightenment” to reach
report, Rethinking Construction, the “plateau of productivity”? Plateau of productivity
enthusiasts claimed the quality, To find out, this study rehearses
speed and cost savings achievable the potential benefits of modular
with factory production of construction and explores the
modular units offered irresistible barriers that have limited uptake of Slope of enlightenment
benefits to the building industry. prefabrication in the UK – including
The anticipated revolution did a failure to understand the business
not happen, and those who model and an overwhelmingly Trough of disillusionment
experimented found the benefits negative public image. It examines
did not always materialise. where successes have been
The pattern has all the hallmarks achieved, where they have not and Modular trigger
of the Gartner hype cycle for where the greatest potential for
emerging technologies, which future development is. TIME
WHAT IS MODULAR CONSTRUCTION?
Modular construction describes substantial Other volumetric modules are “frame + infill”, structural infill panels are inserted between the
elements of a building that are factory-produced using posts and beams – typically formed from posts to form the walls, providing greater flexibility
and delivered to site for assembly. It comes in hot-rolled steel sections – to frame the units. Non- in room layout than a solid-wall module. Floors and
several forms – the principal focus of this article ceilings span to the perimeter of the frame.
is volumetric modular systems. n Panel systems (or flat panel systems) – 2D
n Volumetric modular systems – prefabrication panels are prefabricated, delivered to site and
is used to create complete 3D structural units, craned into position, then connected to form
usually using steel framing or light-gauge steel a structure. Materials are typically precast
sections but also precast concrete, timber or a concrete, timber, cross-laminated timber or
combination of these. structural insulated panels. Finishes and services
The modules may be fully fitted out in the factory, are usually installed on site after assembly.
including services and internal fixtures and fittings. n Pods are relatively small prefabricated
They are then driven to the site and craned into modules, usually fully fitted out, which may be
position, with combinations of modules – often used in conjunction with another construction
stacked – used to create larger buildings. method. Common examples are bathroom or VISION MODULAR
Some volumetric modules have load-bearing kitchen pods. TION /
walls. They rely on the wall panels for structural n Hybrid systems may combine volumetric or
strength, either for vertical load bearing or for panelised systems with other precast elements
diaphragm action to resist lateral loading. Mapleton Crescent, by Vision Modular and/or a primary structural frame.
TIDE CONSTRUC
27.07.2018 BUILDING MAGAZINE
economics / construction methods / 47
02 / POTENTIAL BENEFITS
Speed explained in the next section, below. Health, safety and wellbeing of staff can be more easily achieved, resulting
Programme savings of up to 50% are Savings in labour costs are possible, In the controlled factory environment, in improved quality of construction.
possible compared with traditional by more efficient use of labour or by risks such as working at height and There is a reduced risk of moisture
forms of construction. Furthermore, the avoiding city centre wages. Standardised exposure to bad weather, noise and ingress during construction, and
programme can be more predictable details can reduce overall design fees dust are reduced or eliminated, workmanship is not affected by
than when using conventional methods and a more predictable construction while other hazards can be better bad weather.
– if errors do occur during fabrication, programme reduces the risk of increased identified and mitigated. Fewer Reduced numbers of errors mean
the effect on the overall construction costs due to delays on site. trades and personnel are required in fewer snags and fewer defects
process can be more easily managed, The shorter construction programme the more dangerous site environment. on handover, and consequently a
since repairs are limited to one particular can also reduce the costs of site Also, the workforce in a static factory reduction in the associated costs
module and can be completed offsite. management and facilities costs, while has longer-term job prospects, and delays.
producing a faster return on investment, extending beyond completion of
Space with reduced financing costs. the current project. Sustainability
A smaller site area is required on site The manufacturer’s cost base More construction offsite means less
as fewer construction materials are should be more predictable as there is Quality waste as the controlled conditions
stored there. With careful management greater control of the workforce, who Assembly in a factory can consistently enable work to be more precise and
of the delivery and installation of are likely to be on more permanent or deliver airtight, thermally efficient there are fewer mistakes, and waste
modules, temporary storage can be fixed contracts, than with site-based construction, with lower running produced in a factory can be more
minimised or removed altogether. alternatives where operatives move costs. The air gaps between modules easily recycled. On a residential
from site to site looking for better pay in volumetric construction assist in building, most of the lifetime energy
Cost savings and conditions. Transferring from trade- providing acoustic separation between use is due to space heating: the better
The repetitive nature of modular based delivery to a more task-trained units. Factory production can deliver airtightness and thermal performance
construction, which is tailored to a operative scenario not only reduces more durable construction, which obtainable in factory conditions,
factory environment, creates lower cost but also improves access to labour requires less maintenance. particularly with volumetric modules,
costs – though these savings are and can help alleviate some impending In a controlled factory environment, translates into lower energy use and
not always achieved in practice, as construction skills capacity issues. strict quality assurance procedures lower running costs for occupants.
03 / OBSTACLES TO ADOPTION
Cost to the client. So although costs may come down, competitive and behave as expected; passing
Feedback suggests that in some areas such as prices often remain high – though this “risk savings on to “good” clients that adopt the new
Ministry of Defence work, student housing margin” is difficult to identify because modular practices needed to maximise the benefits of
and even budget hotels, modest savings are being contractors do not provide detailed cost data in offsite (see figure 2, overleaf).
achieved, but in the mass market and the same way as traditional contractors.
the emerging build-to-rent (BTR) sector On top of this, many clients fail to understand Negative public perception
capital costs remain higher than for that modular construction requires a different The public’s distrust of modular lies in the history
traditional contractor delivery. approach to procurement, in which details are of prefabrication. Back in the mid-19th century
The explanation lies in the nature of the designed with factory construction in mind and there were spectacular successes: Joseph Paxton’s
business model and – in particular – the current design is finalised before procurement. This leads Crystal Palace in Hyde Park for the 1851 Great
lack of competition in the modular market. to avoidable extra costs due to late changes and Exhibition and Isambard Kingdom Brunel’s
The suppliers of volumetric modules are costly detailing. wooden Renkioi Hospital built during the »
operating a manufacturing business with As a result of these factors, some clients
large initial investment and relatively high see no cost savings, or even pay more, though they
overheads associated with running the factory may still receive the programme and
and its fixed labour force. They need, above all, quality benefits. Indeed, many early users see
a steady flow of work. Keeping unit costs low speed of construction (and hence an early
depends on high utilisation, which can be much return on investment) as the key driver, so
more difficult to achieve in construction than in, driving down construction cost is seen to be
say, a car factory because the offsite manufacturer of lesser importance.
is multiple steps removed from
the commercial/sales decision making. Competition
Consequently there can be large variations in There are a limited number of suppliers, partly
unit costs depending on the level of utilisation. If because of the reasons above, and capable
suppliers with low utilisation discount too much competition is lacking (see table 1, page 50).
to generate demand, they go bust, so they tend to Suppliers try to maximise their profits, so
keep their prices up (see figure 2, overleaf). in a supply-limited market, prices will rise
When the factory’s utilisation rate is high, unit to match the cheapest alternative, usually
costs come down. But this corresponds with conventional construction.
periods of high demand, so there is no financial As both demand and capacity for offsite John Dodgson House, a budget summer residence
incentive for the supplier to pass on the savings grows, the market will hopefully become more owned by UCL and built by Premier Modular
PREMIER MODULAR
BUILDING MAGAZINE 27.07.2018
48 / economics / construction methods
» Crimean War. However, both enterprises for modular, the space planning, detailed with that supplier are particularly important.
excluded Britain’s architectural establishment, design and service integration all need to be At present, most UK suppliers use simple forms
which may help explain why prefabrication completed earlier than on traditional projects, of construction, largely because the industry
was not repeated for the next half century, and since the costs of incorporating late design is still in its infancy and suppliers are avoiding
rarely thereafter. changes to the modules can be very high. over-investing in heavily automated fabrication
In the 1940s, post-war prefab housing was built Clients who realise this too late find that their systems. This may help limit the supplier’s risk,
quickly to meet an urgent need when materials, costs rise, or that their required changes are but it also limits the benefits that full automation
labour and money were in short supply. Modular too expensive to implement. could bring.
came to mean temporary accommodation such Of course, suppliers try to keep their factories
as site huts. Consequently, prefabrication and full and their utilisation rates high, so once a Accreditation
modular came to conjure up images of cheap, programme of construction has been agreed, Building regulations, planning permission and
cramped construction. it can be difficult to alter the rate of delivery. insurance and mortgages for residential property
The stereotyping has been reinforced by the Acceleration may be impossible due to other can be a barrier, as they are with any construction
way the recent British volumetric modular orders, and delay may mean “missing the slot” innovation, because they take time to catch up.
construction industry has developed – emerging and incurring contractual penalties. Mortgage lenders generally expect a design
from the temporary accommodation market, life for the structure of at least 60 years, while
sometimes with few efforts to disguise the fact. Procurement non-structural components are expected to last
Some manufacturers may be unaccustomed Once engaged with a particular supplier, there no less than 15 years. Durability of new systems is
to appointing architects with experience of is usually very little scope to source modules difficult to demonstrate, but suppliers are able to
designing high-quality, permanent buildings and, from an alternative company if the original address concerns with the Buildoffsite Property
conversely, few architects are familiar with the supplier fails to perform. So careful choice of Assurance Scheme (BOPAS) certification or
design of volumetric modular units. supplier and developing a close relationship alternative assurance schemes.
Design
The most obvious constraint is how large and Figure 2: Explanation of utilisation and effect on cost and risk
heavy a module can be. To be transported by lorry
each module must be within the limits of 2.9m A) Current volumetric market position of ‘inconsistent utilisation’
wide, 4.2m-4.5m high and 18.75m long (or a little
larger for an “abnormal load”). A lightweight
volumetric unit can usually be lifted by a medium-
to heavy-duty all-terrain mobile crane, although (F)
incorporating concrete floors into the modules 1
Optimum utilisation A
can double the load. There is also a limit to the (C)
height to which units can be stacked, although the (D) (B)
limit depends on the type of module and the form
of construction. (£) (D)
There can also be constraints on layouts.
Some forms of modular construction require Optimum cost threshold (E)
load-bearing partitions to stack vertically through
the height of the building, with limited scope (A)
to accommodate large openings in these walls.
These also limit the flexibility to alter the layout
between floors, meaning, for example, that a late Duration
change in the mix of apartments for a housing
block would have a major effect on the design and Risk margin + profit (D)
could also require further changes to the layout Optimum utilisation (A1)
of apartments on the floors above and below. Utilisation (A) Excess cost driver by low utilisation
Greater flexibility can be achieved by combining Actual cost of manufacture (B) Optimum ‘cost’ threshold (E)
factory fabrication with sub-assembly into larger Actual price to client (C) Comfort/confidence
units on site. (period between utilisation) (F)
Many facade types and finishes used with
modular construction reflect the industry’s Notes:
background in temporary accommodation, with Actual cost (B) driven by utilisation levels (A).
a perception of mere functionality, and lack of Actual price level (C) driven by confidence – the shorter the period (F) drives a lower risk margin (D) and
durability. However high-quality finishes can be ultimately a lower price.
achieved, and a panellised facade system can be
fixed to the units after they are installed on site. In periods where manufacturers risk margin (D) and optimum cost threshold (E) drops below the actual cost of
manufacture (B), losses will be made which if (F) remains wide then a company risks going under.
Flexibility The answer/solution is to be able to control utilisation levels through a consistent pipeline:
With traditional construction it is common for n Decrease (F)
design to overlap with construction, such as the n Reduce (B) towards level of (E)
design of kitchens and bathrooms continuing n Ability to reduce (D)
while the structural frame is erected. However, n Reduction in (C)
27.07.2018 BUILDING MAGAZINE
economics / construction methods / 49
04 / KEY DRIVERS ON RESIDENTIAL PROJECTS
Figure 3: Relative importance of key drivers
Graphs A-E illustrate the key drivers on a range of
A Housebuilder B Build-to-rent developer residential products, shown on a scale of one to 10
Time Time against the headings of cost, quality, and time.
10 10
8 8 For example, a housebuilder places high emphasis
6 6 on cost base, but less on programme due to a
4 4 consistent pipeline and a requirement to phase
2 2 units to market, whereas a build-to-rent developer
0 0 places much greater importance on bringing units
to market quickly.
Quality Cost Quality Cost
C Student housing D Mass market developer E Prime residential developer
Time 10Time 10Time
10
8 8 8
6 6 6
4 4 4
2 2 2
0 0 0
Quality Cost Quality Cost Quality Cost
05 / WHAT IS MODULAR CONSTRUCTION SUITABLE FOR?
Success stories Accommodation Modernisation),
Take-up has been generally at the an accommodation programme for
lower end of the market, wherever the Ministry of Defence taking in
repetition is achievable, speed 52 locations across the UK.
of construction is particularly
desirable and high quality is not Areas for improvement
necessary. Examples include It has had little or no take-up in
student accommodation, where commercial offices, where large,
Vision Modular has delivered a open interior spaces are required
number of successful schemes and where, most significantly, the
such as Apex House and Felda market is highly cyclical, providing
House in Wembley, north-west little or no potential base-load of
London, as well as Chapter in utilisation for a factory.
Lewisham, south-east London. Nor, so far, has modular had much
In key worker accommodation impact in markets where speed
both Premier Modular and of construction is less critically
Caledonian have delivered important, including the middle to
VISION MODULAR schemes at Hinkley Point for upper range of the housing market
TION / construction workers at the (apart from details such as toilet
nuclear power station. Pocket pods and prefabricated facades).
Living’s Mapleton Crescent Benefits have been
Apex House, Wembley, student accommodation, scheme in Wandsworth, south- demonstrated in terms of
TIDE CONSTRUCwhich is the tallest modular building in Europe west London, was completed by snag-free compliance and
Vision Modular. functionality, but few are
Modular’s level of suitability three areas – time, quality and cost Budget hotels such as Premier convinced that modular can
for different projects can be – but in practice there is always a Inn and Jurys Inn have been provide the less tangible aspects
explained by the traditional trade-off. Modular offers potential constructed using volumetric. of high-quality development – to
construction triangle of quality, benefits in all three areas, as Other notable schemes include create spaces that people really
cost and programme (figure 3, explained in the “Potential a number of schools and want to live and work in and that
above). The ideal is to optimise all benefits” section (page 47). Project SLAM (Single Living people delight in. »
BUILDING MAGAZINE 27.07.2018
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