Modern methods of construction
Modern methods of construction can provide good quality homes
with less on‑site labour, in a shorter time, with at least the same
building performance and at similar cost when compared to more
established techniques - but poor project planning can reduce
these benefits.
These conclusions to our 2006 report Using modern methods of construction to build homes
more quickly and efficiently will come as no surprise to those
of you who have been following the debate on modern methods of
construction. Advocates of new techniques have made similar claims
for many years.
Background to the report
We launched our study because the then Office of the Deputy
Prime Minister and the Housing Corporation asked us to examine how
to get best value when using modern methods of construction. At the
time of the report, they had been spending £1.1 billion a year on
building affordable housing using modern methods of construction,
including £0.5 billion on off-site manufacturing approaches and
they planned to spend more. Our study is also relevant to the wider
off-site manufacturing industry, estimated to be worth £2billion to
£3 billion annually [Footnote
1]
What exactly did we do?
We set about our work by pulling together a wealth of outside
expertise. We formed a team of consultants in construction process
modelling, building cost calculation, modern methods of
construction, durability assessment and on-site activity analysis.
We held four workshops involving nearly fifty practitioners, who
generously donated their expertise and knowledge, and we discussed
details further with many of them.
The heart of our research is a set of project plans that take
real-life practice from a range of developers and express it in
terms of a standardised development to allow comparability. The
standard is based on a typical development undertaken by Registered
Social Landlords, comprising 22 dwellings in a low rise development
of flats and terraced houses.
The project plans, which are fully costed, set out how to
complete the same development using brick and block, open panel,
hybrid and volumetric techniques. They represent typical average
plans of experienced developers. Our approach to costing was to
obtain prices for off-site elements from manufacturers, to
calculate labour costs from project plans and to add on-site
material costs for what was not provided in off-site elements. We
validated our calculations by comparing them with results from
actual practice.
Labour and time
Our research showed that, compared to more traditional
techniques, modern methods of construction can reduce on-site
labour requirements to less than a quarter and on-site time to less
than a half. These reductions are not magic: they result from some
work taking place off-site. They bring real benefits because
off‑site work involves different labour that is not as stretched as
the on-site workforce [Footnote 2]
and off-site work can be taken off the overall critical path
providing it is planned properly. Modern methods of construction
can therefore make better use of scarce labour and reduce total
development time.
Benefits can be lost if project planning does not take account
of the construction technique. We heard of one development where
the superstructure all went up in 2 weeks. Then nothing happened
for 8 weeks because nobody had told the following trades that the
process was different and they would have to start earlier. Poor
planning and communication failure wasted much of the benefit in
using modern methods of construction.
More generally, our research shows that design and manufacture
of off-site elements must start as soon as outline planning
permission is obtained. This has two important implications. First,
supply chain management, in particular the interface with planning
authorities and with manufacturers, is vital. Second, early design
freeze is critical because design changes after manufacture has
started will be expensive.
Cost
Our analysis confirmed that modern methods of construction can
be cost‑competitive in the right circumstances but hybrid and
volumetric techniques are more expensive on average than other
techniques. A range of circumstances, such as poor soil conditions
and restricted working space, favour modern methods of construction
but other factors, including late design changes and late
contractor appointment, have the opposite impact. All these
conditions affect the relative cost‑effectiveness of different
construction methods.
Some financial benefits of modern methods of construction can be
overlooked. Two come from faster completion (earlier rent receipts
and a shorter borrowing period) and two come from the quality
control in off-site manufacture (less snagging and less on-site
inspection). These benefits close about a third of the average cost
gap between modern methods of construction and more established
techniques.
Quality
We found that modern methods of construction can deliver at
least as good quality as more established techniques providing they
are specified appropriately. We considered quality under the
headings of durability (will the building last as long?), whole
life costs (will it cost the same to maintain?) and performance
(will it operate as well?).
Risk management
Modern methods of construction substantially change the risk
profiles of home building projects, with risks migrating from later
stages to earlier stages. Our report includes a detailed table
illustrating how risk management changes when using modern methods
of construction.
A version of this article first appeared in the magazine
Sustain in 2006.
- [back from footnote 1] Keynote address
by Richard Ogden, Chairman of Buildoffsite, at the Futurebuild
Conference, February 2006
- [back from footnote 2] “CIOB reveals
results from skills shortage research”, Chartered Institute of
Building Press Release, 15 August 2005