26 February 2020
Off-site construction and pre-manufacture
The following is an extract from TRADA publication Off-site and industrialised timber construction: Delivering quality and efficiency 2nd edition. Find out more about the publication
Off-site construction is based on two key principles: efficiency and quality. It involves the manufacture and pre-assembly of components, elements or modules before installation into a final location. The construction value added on site is less than 40% of the final construction value at completion .
Off-site construction can be split into four broad categories of panelised, modular/volumetric, hybrid and sub-assemblies/components, of which there are sub-categories relative to the level of enhancement (Figure 2.1). Off-site construction allows parts of the building to be pre-manufactured in an environment suited for effective production, where, if appropriate, advanced equipment can be used to increase productivity.
Off-site construction also improves working conditions by taking construction processes to a clean, controlled environment, unaffected by climatic conditions. Ideally as many parts of the building will be finished to as high a level of completion as possible to minimise work on site. A section below contains a range of terminologies often used to describe off-site or industrialised forms of construction.
Forms of off-site construction
1. A 2D panelised frame
2. Modular or volumetric 3D construction
3. A hybrid system using 2D and 3D construction
4. Sub-assemblies and components
Other off-site terminologies
Prefabricated (prefab) construction
Prefabrication covers off-site prefabrication of materials and parts, prefabrication of components and sub-assemblies, as well as volumetric units or modules.
Modularisation of construction is a way of reducing complexity but maintaining customised solutions. The Modular Building Institute (MBI) defines modular construction as an off-site process, performed in a factory setting, yielding 3D modules that are transported and assembled at the building’s final location.
Industrialised building systems (IBS)
IBS represents the prefabrication and construction industrialisation concept. The term has been used as a shift away from prefabrication, with additional emphasis on improved productivity, quality and safety.
Open building manufacturing
Open building manufacturing applies production theory to construction, employing standardised components that can be configured and assembled to provide a specific end result.
A generic term for all processes that reduce the level of on-site labour intensity and delivery risk. This includes a ‘design for manufacture and assembly’ approach at all levels, ranging from component-level standardisation and lean processes (see Chapter 5), through to completely pre-finished volumetric solutions. It also includes any element of on-site or adjacent-to-site temporary or ‘flying’ factory or consolidation facilities, which de-risk in-situ construction, improving productivity and predictability.
Modern methods of construction (MMC)
MMC seeks better products and processes. It aims to improve business efficiency, quality, customer satisfaction, environmental performance, sustainability and the predictability of delivery timescales. MMC is, therefore, more broadly based than a particular focus on product. It engages people to seek improvement, through better processes, in the delivery and performance of construction .
Integrated project delivery
IPD is a project delivery approach that integrates people, systems, business structures and practices into a process that collaboratively harnesses the talents and insights of all participants to optimise project results, increase value to the owner, reduce waste and maximise efficiency through all phases of design, fabrication and construction .
Smart construction is building design, construction and operation that, through collaborative partnerships, makes full use of digital technologies and industrialised manufacturing techniques to improve productivity, minimise whole life cost, improve sustainability and maximise user benefits .
Prefabricated prefinished volumetric construction (PPVC)
A construction method whereby free-standing 3D modules are completed with internal finishes, fixtures and fittings in an off-site fabrication facility before it is delivered and installed on site .
Current UK context for off-site construction
In 2015 the UK construction market was ranked fifth out of the eight nations that account for 70% of the $10 trillion global construction market . In 2017 the UK population was 64.2 million, projected to increase to 72.1 million by 2047 . This figure, combined with changing demographics resulting in a higher proportion of one- and two-person households and assisted-living requirements , will continue to place significant pressure on existing societal infrastructure such as schools, healthcare and housing.
There are 1.5 million households on the UK housing waiting list; the total number of new homes required to be built is predicted to be 295,000 per year until 2037, plus 15,500 care and retirement buildings by 2035 . Given this context, the most recent UK Government Construction 2025 strategy  set out improvement targets of:
- lower costs: 33% reduction in both the initial cost of construction and the whole-life cost of assets
- faster delivery: 50% reduction in the overall time from inception to completion for new-build and refurbished assets
- lower emissions: 50% reduction in greenhouse gas emissions in the built environment
- improvements in exports: 50% reduction in the trade gap between total exports and total imports for construction products and materials.
Recent estimates of off-site construction in the UK are approximately £1.5bn to £6bn per year in terms of construction output of a £90bn construction market  . An accurate valuation of the sector is difficult given its relatively fragmented nature and the ambiguity of what constitutes off-site when considering the level of enhancement or value added.
However, it is apparent that, for off-site construction to be a vehicle for delivering the built environment, it requires large-scale operation. For this to take place there must be a change in construction culture, including multi-skilling, interdisciplinary collaboration and greater flexibility within a number of job roles. These drivers, as well as others such as regulatory, digitisation/Building Information Modelling (BIM) and the need for improved levels of productivity, must intersect appropriately within the given economic context .
It has been demonstrated throughout construction history that successful construction methods only endure when positioned at the correct intersection of such drivers with the overall economic context critical for scale . Currently in the UK there is certainly a need and Government willingness for off-site construction. In 2017 the Government announced that the Department for Transport, the Department of Health and Social Care, the Department for Education, the Ministry of Justice, and the Ministry of Defence would all adopt a presumption in favour of off-site construction by 2019 across suitable capital programmes, where it represents best value for money .
The UK Government has now committed to changing its procurement model in favour of off-site construction by means of ensuring the public sector can procure for whole-life value rather than upfront cost. A House of Lords Science and Technology Select Committee – Off-site manufacture for construction: Building for change  – has endorsed this approach and encourages future research and development of off-site construction to focus on demonstrating the full lifetime value that it can bring; it also encourages the UK Government to consider tax incentives.
|You have been reading an extract from TRADA publication Off-site and industrialised timber construction: Delivering quality and efficiency 2nd edition. Find out more about the publication|
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