Unit 35: Alternative Methods of Construction
W3 and 4, LO2: Explore alternative construction
methods which are fit for purpose in a given
context.
Dr Asal Pournaghshband (FHEA, CEng)
Spring 2022
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Overview:
• Assessment criteria
• Modern construction techniques/materials
• Modern methods of construction:
• Key findings of Survey by NHBC
• History
• Definition of modern methods of construction (categories)
• MMC example: Thin joint blockwork basics (End of Week 3)
• Use and consideration of different types of MMC
• Types of panelised systems used
• Main reasons for considering MMC
• Benefits of MMC in practice
• Experiences of volumetric construction and pods
• Value engineering
• Student In-Class Practice (Both week 3 and 4)
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LO2: Explore alternative construction methods which are fit for purpose in a given
context.
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Introduction:
While technology and construction have progressed rapidly in recent years,
allowing structures to be built taller and faster than ever, remnants of colossal
ancient monuments remind us that construction techniques/materials from as
long as hundreds of years ago had enormous merit as well.
Material: many of the innovations of antiquity serve as foundations of modern
construction, with the Roman invention of concrete serving as a cogent example.
Construction techniques: Other essential ancient construction techniques, such
as the arch and the dome, are now often considered stylistic flourishes, with
designs like the Met Opera House reinterpreting classical typologies in a modern
context. Yet perhaps the most relevant reinterpretations of ancient construction
today are those that do so in the interest of sustainability, renouncing highenergy modern construction methods in favor of older, more natural techniques.
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These reinterpretations are ranging from the revived use of ancient materials to
renewing ancient construction techniques.
For example, a new type of rammed earth construction reimagines ancient
sustainability from a material standpoint, transforming traditional rammed earth
into the stronger cement-stabilized rammed earth (CSRE). Originally consisting of
soil, water, and a natural stabilizer (animal urine, animal blood, plant fibers, or
bitumen), having been used in monumental ancient projects ranging from the
Great Wall of China to Alhambra. However, CSRE mixes soil, water, and cement
instead, improving the material’s strength by orders of magnitude. Yet the main
ingredient still being local soil, CSRE thus crucially reduces the negative effects of
transporting other materials. CSRE is also cheaper than many other more
common building materials, making it a sustainable option for affordable housing
as well.
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Alhambra, Granada, was built chiefly between 1238 and 1358.
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Nubian vaults, which were used to build houses in ancient Egypt and involve the
construction of vaulted roofs using dried mud blocks, both utilize local materials
and eliminate the need for timber. Nubian Vault Association (AVN) has been
instituting the Nubian vault as a sustainable solution by training locals in its
construction techniques, an effort that was recognized in 2016 by the World
Habitat Awards.
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CobBauge is another sustainable construction material that has been investigated
in recent years by the University of Plymouth. Cob has been used to build
residential houses in England and France for hundreds of years, but because of its
weaker thermal and structural properties, usually fails to satisfy modern
construction regulations. The University of Plymouth has been investigating new
cob mixes that will satisfy building regulations and allow contemporary architects
to again utilize the material. Consisting of local soils, these new cob mixes are
hoped to reduce CO2 emissions and decrease construction waste as well.
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However, ancient construction materials and techniques are not only valued for
their sustainability – building methods like the ancient Chinese dougong may be
thousands of years old, but continue to be reinvented today for different
structural and aesthetic needs. Consisting of a wooden bracketing system that
once supported overhanging pagoda eaves without the need for nails,
contemporary architects like Kengo Kuma read both tradition and aesthetic
possibility in the ancient dougong system, Kuma having designed the
unconventional Café Kureon using this technique.
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Modern methods of construction:
Alternative forms or modern methods of construction (MMC) have a long history in
the UK. In the post-war period much use was made of a variety of innovative housebuilding systems and from time-to-time since then, there have been surges in
interest. It aimed to establish current attitudes to MMC amongst the larger house
builders and housing associations
Key findings of Survey by NHBC (National House Building Council) Views from the
industry:
1. 98% of large and medium-sized house builders and housing associations have
used or considered at least one form of MMC in the last 3 years.
2. The most widely-adopted form of MMC is sub-assemblies and components with
two-thirds having used them for at least one home during 2015 including door
sets, timber I-beams, prefabricated chimneys and prefabricated dormers.
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3. The second most popular form of MMC is panelised systems (eg timber and steel
frame), which was used by 42% of respondents during 2015 for at least one
home. In the lead was timber frame which, according to NHBC registration
statistics for 2015, accounts for 15% of UK housing output. In Scotland, where
timber frame is used for three-quarters of new homes, it is not regarded as a
modern method.
4. Only limited use is being made of volumetric construction (large modules fully
fitted out on-site) and pods (room-sized modules normally bathrooms or
kitchens) with 6% and 7% of organisations having used these methods
respectively one or more times in 2015. Use tends to be concentrated in
apartment buildings in London and the South East.
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5. The majority of organisations surveyed consider themselves to be ‘late adopters’
or ‘followers’ of volumetric construction, pod and panelised forms of MMC,
watching the success of others before making the decision to move away from
conventional cavity masonry construction. Only 10% of house builders
considered themselves to be ‘market leaders’, leading innovation.
6. One of the key attractions driving the use of MMC is the perceived ability to build
more quickly.
7. It was also felt widely that MMC would have a role to play in improving the
quality of construction and overcoming current shortages in the availability of
skilled labour. For those already using MMC these perceived advantages were
being realised in practice.
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8. There is some evidence of MMC leading to a reduction in costs and improved
profitability, with 44% of house builders and 27% of housing associations
pointing to benefits such as reduced preliminary costs, improved cash flow and
faster sales revenues.
9. Most participants expect the role of MMC to grow or remain static over the next
3 years; only 3% expected it to decline. Over half expected the use of panelised
systems, in particular, to increase during that period.
10. If there is to be greater use of pods and full volumetric construction, risks within
the supply chain need to be addressed. There are concerns about the size,
quality and capacity of suppliers and their ability to sustain high volume output.
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History:
The history of innovation in construction in the UK is long, dating back to before the
Second World War, but comparisons with the current housing market challenges are
striking. In the post-war period, there was a housing crisis with over 200,000 homes
estimated to be required quickly; Prime Ministers were heavily involved setting up
cross-party committees to examine solutions and Government program were being
rolled out to build ‘new technology’ homes. In 1944 this was known as the EFM
(emergency factory made) program which, despite a good start, eventually delivered
153,000 ‘temporary’ prefabricated homes. Alongside these were ‘permanent’
nontraditional homes of which almost 450,000 were built in the decade following
the war.
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More recently the need to increase off-site construction in the housing sector, and
the construction industry generally, was discussed in the Latham Report,
Constructing the team, Joint review of procurement and contractual arrangements in
the United Kingdom construction industry published in 1994, and the Egan Report
Rethinking construction published in 1998. By drawing on experiences of other
industries such as manufacturing, these reports sought to identify how to improve
efficiency, reduce waste and make the industry more responsive to customer
needs
Currently we still see an industry that has largely continued to use masonry cavity
wall construction for low-rise residential new build. The success of off-site
manufactured homes seen in other parts of the world, such as Scandinavia and
Japan, has not generally been replicated in volume in the UK.
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The pressures in today’s housing market are:
• high customer demand with shortfalls in supply
• shortages of skilled labour and materials
• a drive for construction speed
• achieving high quality and energy performance
• the elimination of waste.
These pressures have echoes of past challenges which could be expected to
encourage use of off-site methods, now referred to as MMC. So how is the industry
responding?
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Definition of modern methods of construction (categories):
The term modern methods of construction (MMC) embraces a number of
approaches involving off-site manufacture or assembly. The definitions of MMC have
varied over the years but for the purposes of this research, the following types of
MMC were used
volumetric construction
pods
panelised systems
sub-assemblies and components
site-based MMC
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The types of MMC used in the research are based on those used by Building
Research Establishment (BRE) in the National House Building Council (NHBC)
Foundation report A guide to modern methods of construction. This classification
also includes innovative on-site methods designed to improve efficiency and/or
reduce waste, such as thin joint blockwork. The definitions and appropriate images
were shown to participants as the basis for questions about approaches they had
used, and the extent of their use.
Note:
Thin joint blockwork: Thin layer mortar is a pre-mixed cement-based product that
only requires the addition of water to make an easily-applied mortar. It differs from
general use mortar in that it sets more rapidly, thus giving early stability to the
construction. It provides an alternative to traditional sand/cement mortar and allows
the depth of the mortar to be reduced from at least 10mm to 3mm or less.
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MMC example: Thin joint blockwork basics
One of the biggest developments in modern masonry construction was the
invention of aircrete blocks in the 1920s (although they weren’t widely used in the
UK until the 1960s). These lightweight aerated products offer an appealing
alternative to dense units. They’re easier to handle, quicker to build with and yield
better insulation levels – something that’s particularly crucial as we move towards
ever-lower carbon emission targets for new homes.
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MMC example: Thin joint blockwork basics Cont.
• The system uses a special cement-based, quick-set adhesive that’s just 2mm-
3mm thick (as opposed to the standard 10mm mortar beds). This is delivered in
25kg powder bags, so your trades simply add water, mix in a bucket with an
electric stirrer and spread the adhesive using a proprietary applicator.
• The lean bedding layer helps to ensure a faster build and also cuts down heat
loss – as there’s simply less potential for air leakage through the joins. In fact,
aircrete and thin joint are perfect partners, as the blocks are accurately
dimensioned to the tightest possible tolerance (known as Thin Layer Mortar B).
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Use and consideration of MMC:
This section examines the use of construction methodologies in residential new
build as recorded by NHBC. It breaks down the use of MMC by type and
geography, and looks in detail at the use of panelised systems and offsite
manufactured components. It indicates where decisions on construction
methodology are being made and the willingness to innovate amongst those
building new homes.
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The use of timber-framing or light steel-framing methods for the structure of
homes represented about 16% of the new build market in 2015, having
declined from a high of 24% in 2008. NHBC’s statistics do not, however, record
the extent of use of sub-assemblies and components, which are used by more
organisations involved in new build than structural forms of MMC. The UK
figure masks differences in construction method between countries. In
Scotland, timber frame is the conventional approach, where it accounted for
75% of construction methods amongst NHBC-registered new build homes in
2015. In Wales timber frame has experienced a higher share than in England,
where market share is at its lowest.
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Use and consideration of different types of MMC
The majority of house builders and housing associations are using, at least one
MMC approach within their recent build programs. Of the large and mediumsized house builders and housing associations surveyed, only two said they had
not used or considered at least one form of MMC in the last 3 years. The most
used are sub-assemblies and components, installed by about threequarters of
the house builders and just under half of the housing associations in 2015.
Panelised systems are the next most used MMC type.
Very few have used full volumetric construction or pods in the 3-year period
2013 to 2015 (Figure 5). However, these are being considered for future use by
over a third of organisations: 37% are considering, or may consider, volumetric
construction and 28% are considering, or may consider, using pods (sometimes
known as semi-volumetric). But opinion remains split with over half in each
case having already rejected or unlikely to consider use at all.
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Encouraged by historical Government funding conditions, housing associations
might be expected to have the most experience of MMC; but it appears that more
private sector house builders have been using pods, sub-assemblies and
components (Figures 6 and 7). The apparent lower use by housing associations may
be due to their procurement of new homes through Section 106 agreements or
through design and build contracts, meaning that they may not always select the
method of construction used. By region, use of volumetric construction and pods
has been almost entirely in London and the South East. Use of panelised system
MMC is higher in Scotland than elsewhere due to the well-established tradition of
building with timber frame. Use of off-site manufactured sub-assemblies and
components is also highest in Scotland.
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Types of panelised systems used:
Panelised systems in use include ‘open panels’ (i.e. without plasterboard linings
factory fixed) and ‘closed panels’ (i.e. plasterboard fixed in the factory) in both
timber and light steel framing. 42% of the organisations interviewed used panelised
systems in 2015. The main type used is open panel timber frame, installed by just
over two-thirds of panel system users in the last 3 years (Figure 8). 39% of
organisations have used closed panel timber frame and 33% have used SIPs over
the same period. This use of panelised systems is set to continue in 2016 with 49%
expecting to use open panel timber frame, 32% closed panel timber frame and 22%
open panel light steel frame. 32% said they are likely to use closed panel timber
frame in 2016.
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Types of panelised systems used:
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Main reasons for considering MMC:
The main reason for considering use of MMC is to achieve a faster build
programme. The majority of house builders and housing associations identified this
as their main driver and overall two-thirds gave this as one of their top three
factors. Other reasons for considering MMC include improving build quality,
tackling the skills shortage, and improving health and safety. Achieving a fast
weathertight envelope, reducing costs and improving site efficiencies were also
mentioned. Housing associations are motivated by the need to deliver homes
quickly, and cost effectively, and the results suggest they believe MMC will help
them achieve this objective. There is an undisputed need for more new homes and
the house-building industry is steadily increasing its output.
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Benefits of MMC in practice:
For the house builders using MMC, speed of construction had proved to be the
main benefit experienced in practice. Housing associations were less convinced of
this benefit; this may be explained by their lack of direct control over the building
programme, being reliant on their contractors/house builders. Whereas the ability
to achieve a fast weathertight envelope did not rank highly in the drivers to using
MMC, it was commonly reported as a main benefit realised in practice.
Other benefits include improved build quality, site efficiency and health and
safety, and a reduction in labour and site waste (Figure 13). 33% of house builders
(36% of the large and 20% of the medium-sized companies) have found that MMC
has helped towards increasing the number of units they build. However, none of
the housing associations has found this; achieving a faster watertight envelope has
been the main benefit reported by respondents in this group
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Experiences of volumetric construction and pods:
Volumetric construction 34% of those interviewed have used, considered or are
considering using full volumetric construction for apartments and/or houses. Most
of these organisations are in London and the South East, a small number
elsewhere in England and Wales and none in Scotland. 12 organisations have used
volumetric construction at least once in the last 3 years and their mixed
experiences are summarised in Figure 14. One-third of the organisations had a
positive experience, but the remainder were less positive as they have not
encountered the expected benefits. Their experience has also highlighted the
importance of paying detailed attention to co-ordination and planning well in
advance of construction starting on-site and during construction as well. Feedback
from the survey highlights the following issues:
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Experiences of volumetric construction and pods:
Feedback from the survey highlights the following issues:
There is the need to take design decisions and ‘freeze’ the design at an earlier
stage; this reduces flexibility on-site, particularly for any last-minute changes.
More comprehensive procurement planning of the whole development is
required at the outset.
Despite the planning, more work has been found to be required on-site when
the off-site units are delivered, than was anticipated within the programme.
Cost benefits are not fulfilled in practice; logistics, weather delays and so on,
quickly erode savings.
Low capacity exists within the supply chain, which constrains procurement
choice with some having encountered disappointment with delivery
performance and product quality.
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Pods: 45% of organisations have used, considered or are considering pods in their
new residential build. Of the 28 organisations which have used pods at least once in
the last 3 years most have had largely positive experiences.
Benefits: Amongst the main reasons for using them and the benefits experienced,
they highlighted the improved build quality and reduced levels of snagging,
reductions in site labour and a faster build, with improved programming and
greater overall construction efficiency.
Problem: The main problem was the higher capital cost. Other drawbacks related
to capacity within the supply chain, with a lack of choice of suppliers who are able
to meet the needs of house builders. The logistics of transporting pods to site have
also proved challenging due to the size of each pod. Concerns were also expressed
about where responsibility lies if there are problems during installation.
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Value engineering:
Value techniques applied during the design or ‘engineering’ phases of a project.
Value engineering is based on a methodology developed by Lawrence Miles,
who worked for the General Electric Company in the USA during the Second
World War. Because of the war, there were shortages of materials and certain
finished products. However, manufacturing was running at maximum capacity,
and ideas were needed to expand production.
Miles was responsible for purchasing raw materials for the General Electric
Company and realised if he was unable to obtain one particular material, then it
was necessary to obtain a replacement material which performed the
same function.
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Value engineering:
Later in the 20th century, value engineering started to spread cross the world,
but because of differences between the mentality and behaviour of American
companies compared to European companies, value engineering, as developed
in the USA had to undergo some modification.
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Student In-Class Practice:
You have been employed as an architectural technician working for a large company
which specialises in alternative construction and Brown Fields developments. The
managing director of the company is seeking to expand their client base, and wishes to
have a brochure that will provide information for potential clients to understand the
context in which the company operates. As an example of what the company can
provide, you are also asked to prepare an outline design proposal for a building type of
your choice or high-rise residential /commercial buildings, utilising alternative methods
of construction.
Your brochure should highlight the following:
Explore alternative methods of construction in a historical context and make a
comparison of alternative construction methods that may apply to a specific
building type (chosen by you). Further examine how Alternative Construction
Methods can be used for commercial and domestic contexts. (P3 & P4)
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Thank you.
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