EUR
en
R M Lawson BSc(Eng), PhD, ACGI, CEng, MICE, MIStructE
PJ Grubb BSc (Hons), CEng, MICE
J Prewer DIP Arch (Hons)
P J Trebilcock BA (Arch), DIP Arch (Hons), RIBA
Modular construction uses pre-engineered volumetric units that are installed on site as fitted-out and serviced ‘building blocks’. The use of modular construction is directly influenced by the client’s requirements for speed of construction, high quality, added economy of scale, and opportunity for single point procurement. Light steel framing is an integral part of modular construction, as it is strong, light in weight, durable, accurate, free from long-term movement, and is well proven in a wide range of applications. Modular construction is also widely used in Japan and the USA, where light steel framing is the primary structural medium, and leads to flexibility in internal planning, robust structural behaviour (even in seismic zones), and the possibility of exciting architectural solutions. There are also important opportunities for modular construction in extensions to existing buildings either by attaching units to the sides of buildings or by roof-top modules. This publication addresses the information that is required by clients, specifiers and architects when designing with modular units in residential buildings, in general building construction, and in renovation applications.
The Egan Report ‘Rethinking Construction’ has identified five key drivers of change: committed leadership, a focus on the customer, integrated processes and teams, a quality driven agenda and commitment to people. Modular construction has all of the attributes that are promoted in this report in terms of quality, integrated manufacture, fewer defects, speed on site, and opportunities for innovation in design and in the manufacturing process. It also has broad environmental benefits by reducing waste, minimising environmental pollution and disruption, and ultimately, in being relocatable and re-usable.
This publication has been prepared by Dr R M Lawson and Mr P J Grubb of The Steel Construction Institute, assisted by Mr J Prewer and Mr P J Trebilcock as consultants to SCI. Dr M Gorgolewski of SCI prepared the section on acoustic and thermal insulation of modular construction. The Modular Framing Group (MFG) has provided detailed assistance, particularly in preparing the case studies. This publication is the first in a series on modular construction using light steel framing and gives information suitable for use by all parties at the concept stage of the design process. It is supplemented by: Case Studies in Modular Steel Framing (SCI-P-271) Performance Specification and Design of Modular Steel Framing (forthcoming publication). The work was funded by the Department of the Environment, Transport and the Regions as part of the Partners in Technology initiative, and by British Steel (Strip Products).
SUMMARY
INTRODUCTION
Use of light steel framing in modular construction
Applications of modular construction in buildings
Scope of the publication
Client check-list
INTRODUCTION TO MODULAR CONSTRUCTION
History of modular construction
Types of module
Other modular components
Production and logistics
Advantages of modular construction using light steel
Relevance to ‘Rethinking Construction’
USE OF MODULAR CONSTRUCTION IN THE UK
Hotels and extensions to existing hotels
Residential buildings
Highly serviced units in commercial buildings
Renovation of existing buildings
Pre-manufactured buildings
INTERNATIONAL EXPERIENCE
North American modules
Japanese modules
European experience
MANUFACTURERS OF MODULAR UNITS IN THE UK
Ayrshire Steel Framing
Britspace Modular Building Systems
Metsec Framing
Terrapin - Prospex
Trinity Modular Technology
Volumetric
Yorkon
Other systems
USE OF LIGHT STEEL FRAMING IN MODULAR CONSTRUCTION
Steel grades and sections
Floors and walls
Connections
Roof construction
Opportunities for design by testing
Structural design of walls
Structural design of floors
DETAILED DESIGN OF MODULAR CONSTRUCTION
Requirements for transportation and weather-tightness
Lifting and installation forces
Requirements for overall stability and integrity
Cladding materials
Acoustic insulation of separating floors and walls
Thermal performance
Foundations
Services and drainage
Fire safety
DESIGN AND PROCUREMENT PROCESS
Decision-making process
Procurement process
Procurement of building services
VALUE ENGINEERING ASSESSMENT OF MODULAR CONSTRUCTION
Speed of construction on site
Benefits in the construction operation
Economy of scale
Quality issues
Application to renovation
ENVIRONMENTAL BENEFITS
Environmental benefits during the construction operation
Environmental benefits in use
Environmental benefits in re-use
OPPORTUNITIES FOR MODULAR CONSTRUCTION IN RENOVATION
Modular construction in renovation
Modular toilet and bathroom units
Modular roof units
Modular stairs and lifts
Conversion of redundant buildings into apartments
FUTURE TRENDS
Architectural interest
Standardisation and containerisation
Composite modules
Future growth
‘Total Core’ concept
Modular plant rooms
Stair modules
Bathroom modules
Complex plan forms
SOURCES OF INFORMATION
Manufacturers and suppliers of modular units in permanent buildings
Other companies involved in modular construction
Information on light steel components
REFERENCES
SOURCES OF OTHER INFORMATION
ARCHITECTS’ CHECK-LIST
ACKNOWLEDGEMENTS FOR ILLUSTRATIONS
This publication addresses the design of modular or volumetric construction, in which modular units are pre-engineered in the factory and installed on site to form rooms or parts of complete buildings. The primary structure of these modular units uses light steel components, which are designed for normal structural actions and additional forces due to lifting and other construction operations. The publication provides information suitable for use by architects and specifiers at the early stages in the design process. Details illustrate the range of structural solutions, cladding attachments, and the high degree of thermal and acoustic insulation that can be achieved. A broad value assessment of the benefits of modular construction is included which may form part of a more comprehensive cost-benefit analysis. Examples of recent projects in the UK and other countries demonstrate the current applications of modular construction, which include hotels, residential buildings, renovation by attachments and roof-top extensions, and highly serviced units, such as bathrooms, kitchens and lifts. Construction and environmental benefits are also assessed. Manufacturers’ information and a comprehensive reference list are also given.
Cette publication est consacrée à la conception de constructions modulaires ou volumétriques, utilisant des modules préparés en usines et installés sur le chantier pour former des immeubles complets. La structure primaire de ces modules utilise des composants légers en acier qui sont calculés pour supporter les actions structurales normales et les forces additionnelles dues à la manutention ou à d'autres opérations sur chantier. La publication fournit des informations utiles, pour les architectes et les spécificateurs, dès le début du projet. Des détails illustrent les diverses solutions structurales, les modes de fixation des revêtements et le très haut niveau d'isolation acoustique et thermique qui peut être atteint. La publication contient une large revue des bénéfices que l'on peut escompter avec ce type de construction, permettant ainsi de procéder à une analyse coût-bénéfice précise. Des exemples de projets récents, réalisés en Grande-Bretagne et dans d'autres pays illustrent la brochure. Ces exemples portent sur des hôtels, des immeubles résidentiels, des rénovations d'immeubles et des unités de services tels des salles de bains, cuisines et ascenseurs. Les bénéfices pour l'environnement sont également mentionnés. Une liste de références et d'informations sur des producteurs complète la brochure.
Diese Publikation widmet sich dem Entwurf des modularen oder volumetrischen Bauens, bei dem modulare Bauteile in der Werkstatt vorgefertigt und auf der Baustelle zu Räumen oder Teilen kompletter Gebäude montiert werden. Die Primärstruktur dieser modularen Bauteile besteht aus leichten Stahlbauteilen, die für normale Gebrauchszustände und Montagelastfälle bemessen sind. Die Publikation stellt Architekten passende Informationen im frühen Entwurfsstadium zur Verfügung. Details illustrieren die Bandbreite konstruktiver Lösungen, Fassadenbefestigungen und den hohen Grad thermischer und akustischer Isolation, der erreicht werden kann. Eine breite Wertschätzung der Vorteile der Modulbauweise ist enthalten, die Teil einer ausführlicheren Kosten-Nutzen-Analyse sein kann. Neueste Beispiele von Projekten im Vereinigten Königreich und anderen Ländern verdeutlichen die aktuelle Anwendung der Modulbauweise in den Bereichen Hotels, Wohnungsbau, Renovierung, Anbauten, Aufstockungen und Einheiten mit hohem Installationsgrad wie Bädern, Küchen und Aufzügen. Vorteile beim Bau und im Umweltverhalten werden ebenso beurteilt. Hersteller-Informationen und eine ausführliche Referenzliste sind ebenso enthalten.
Questa pubblicazione tratta la progettazione di strutture modulari ovolumetriche, nelle quali il sistema base viene assemblato in stabilimento e installato in loco per realizzare locali o parti di sistemi strutturali completi. La struttura portante di queste unità modulari è realizzata mediante componenti leggere in acciaio, progettate con riferimento sia alle usuali azioni sia a forze addizionali legate al sollevamento e alle altre operazioni associate all'assemblaggio in opera. Questa pubblicazione fornisce agli architetti e agli operatori del settore utili informazioni relative a ogni fase del processo progettuale. I dettagli illustrano il campo applicativo delle soluzioni strutturali proposte, i sistemi di attacco dei tamponamenti e l'elevato livello di isolamento termico o acustico che può essere raggiunto. Un'esaustiva valutazione dei benefici associati alle costruzioni modulari, eventuale parte di un'analisi costi - benefici di più ampia portata, è inclusa nella pubblicazione. Gli esempi riportati, relativi a realizzazioni nel Regno Unito e in altre Nazioni mostrano le attuali applicazioni di questi sistemi modulari, relative principalmente a alberghi, edifici residenziali, adeguamenti strutturali mediante inclusione di nuovi locali o estensioni dell'uso del sottotetto, e unità di servizio complete come servizi, cucine e ascensori. Sono infine fornite informazioni relative ai produttori unitamente ad un'esaustivo elenco di specifici riferimenti.
Esta publicación se refiere al proyecto de construcción modular o volumétrica, en la que se preparan unidades modulares prefabricadas en taller que luego se instalan in-situ para formar habitaciones o partes de edificios completos. La estructura primaria de estas unidades modulares utiliza componentes ligeros de acero que se proyectan para las acciones habituales así como para elevación y otras operaciones debidas al proceso constructivo. La obra suministra información adecuada para uso de arquitectos y planificadores en las primeras etapas del proceso proyectual. Hay detalles que ilustran la banda de soluciones estructurales y revestimientos aplicables así como el alto grado de aislamiento térmico y acústico que puede conseguirse. Se incluye una primera estimación de los beneficios de la construcción modular que puede tomarse como punto de arranque de un estudio coste-beneficio más preciso. El estado actual en UK y otros lugares, que incluyen hoteles, edificios de habitación, renovaciones y ampliaciones, así como unidades de servicio con baños, cocinas y ascensores. También se indican los beneficios constructivos y medioambientales. Finalmente se incluye información sobre fabricantes y una muy completa lista de referencias.
Denna publikation handlar om utformning av byggnader med volymsmoduler. Modulerna förtillverkas i fabrik och monteras på byggarbetsplatsen samman till rum, delar av en byggnad eller till hela byggnader. Primärstommen i modulerna består av tunnplåtsprofiler som är utformade för att klara såväl normal belastning som belastning pga av lyft och hantering. Publikationen riktar sig mot arkitekter och konstruktörer i ett tidigt skede i projekteringen. Publikationen innehåller detaljer som illustrerar olika konstruktionstekniska lösningar t ex infästningsdetaljer för fasadmaterial samt lämpliga detaljlösningar för att uppnå god värmeisolering och ljudisolering. Publikationen tar upp övergripande fördelar med modulbyggnad som kan utgöra en mer omfattande cost-benefit analys. Exempel på aktuella byggprojekt i Storbritannien och andra länder visar nuvarande applikationsområden av modulbyggnader, t ex hotell, bostadshus, renovering genom tillbyggnad och påbyggnad av befintliga byggnader, men också installationstäta modulenheter som badrum, kök och hissar. Byggtekniska fördelar och miljöfördelar värderas också. Information om tillverkare och en utförlig referenslista inkluderas.
‘Modular construction’ is a term that is used for the factory production of pre-engineered building units that are delivered to site and assembled as large volumetric components or as substantial elements of a building. The modular units may form complete rooms, parts of rooms, or separate highly serviced units such as toilets or lifts. The collection of discrete modular units usually forms a self supporting structure in its own right or, for tall buildings, may rely on an independent structural framework. Modular units may be used for a wide range of building types, from residential buildings to complete fitted-out buildings such as fast-food restaurants. Modular construction should be differentiated from temporary or relocatable buildings, which, although similar in volumetric concept, differ greatly in terms of their quality, structural design, use of cladding materials, and general performance criteria.
The motivation for using modular construction lies in the business-related benefits that make this form of construction more attractive to the client than alternative forms of conventional site-built construction. In such cases, the design decisions are mostly strongly influenced by: Speed of construction on site. Rapid construction leads to business-related benefits to the client, due to early completion and early return on capital investment. Avoidance of disruption and loss of operation of adjacent buildings. This is often important in extensions to existing buildings, such as hotels, and in sensitive sites. Buildings or components with a high degree of servicing. These require careful site installation, and pre-compliance trials, which are better carried out off site and off the critical construction path. A large number of regular or repetitive units. Factory production can facilitate transportation and can achieve economy of scale in production. Planning constraints, such as on delivery times, time of working, noise control on site. A short ‘weather-window’, or other site constraints to the construction operation. Lack of suitable skills at site. This might be the case at a remote site. Client requirements for an exceptionally high degree of quality control. This can best be achieved by off-site manufacture and pre-installation checks. A requirement for a single point procurement route. This can be achieved through a design, manufacture and build service, which the modular industry provides. Security or other related issues on site. Construction operations can be controlled more precisely when modular units are used. It is often thought that modular construction is by definition more expensive than traditional construction. While this may be true for ‘one-off’ buildings, there are considerable economies of scale that can be obtained from greater refinement of the design (often by testing) and by investment in mechanised and possibly automated production. The Japanese house building market is dominated by modular construction, and over 150,000 houses are produced annually in modular form. The high degree of sophistication at the design stage permits considerable input by the purchaser into the choice of finishes and even into the internal layout. The extremely high cost of land in Japan creates an economic imperative to build quickly and to achieve rapid pay-back, which could not be achieved by a conventional construction programme. In the UK, many major companies choose to go the ‘modular route’ because of the greater control they can exert over quality, speed and reliability, which are all business-related benefits. Good examples of the move from conventional to modular construction have been in hotels and fast-food restaurants, where on-site construction times can be reduced by over 60%. Modular construction may be combined with other constructional systems, including: Framed construction. Modular units can be inserted on the floors or roofs of framed structures constructed of beams and columns. Panel construction. Modular units can be used for the more highly serviced elements, while the remaining structure is built from two-dimensional wall and floor panels.
Modular units may also be combined together to form larger rooms. In this case, the length of the modular unit is equal to the span of the floor or roof members forming the completed space. The ‘open’ face of the unit is braced or stiffened during lifting and transportation to provide stability.
Light steel framing comprises cold formed steel sections in C or Z form, or their variants, which are roll formed from galvanised steel strip of 1.0 to 3.2 mm thickness. The members are cut to length and assembled by various connection methods to form the structural framework of the modular units.
The general benefits of light steel framing in the context of modular construction are: robustness during lifting and transportation ease and speed of manufacture (including forming the connections) lightness (for lifting and transportation, and leading to smaller and cheaper foundations) good resistance to vertical and imposed loads suitability for long floor spans high levels of acoustic and thermal insulation can be provided on the framing ease of attachment of a variety of finishes and cladding materials robust connections made on site (by bolting for example) dimensional accuracy and reliable material properties freedom from long-term movement durability and long life fire resistance (steel does not contribute to the fire load). Light steel framing is the ideal framing material for modular construction because of its efficient use of materials and its ability to be integrated into a sophisticated manufacturing process. It is also possible to mix the use of various section types including hot rolled steel members, such as I sections and hollow sections for heavily loaded applications, including at local lifting points. In general, the structure may be ‘over-engineered’ for its normal applications, as sizing is more dictated by stability and rigidity in the lifting and transportation operations. Because of this, the in-service performance of modular buildings is often better than in more traditional buildings.
Modular construction comprising light steel framing has various applications in general building construction, and particularly in residential buildings such as hotels and apartments. Modular construction has not yet penetrated the low-rise housing market significantly in the UK, unlike its success in Japan. The following building types are most appropriate for modular construction: hotels and hotel extensions ‘cellular’ apartment units student residences educational buildings sheltered accommodation, such as old people’s homes toilet units for commercial buildings plant rooms for commercial buildings, hospitals etc. highly serviced units, such as lift shafts and industrial ‘clean’ rooms roof top extensions to existing buildings external modular units in renovation of ‘panel type’ buildings pre-manufactured buildings, such as ‘fast food’ restaurants and petrol stations.
Other applications may be advantageous, particularly where the benefits of speed of construction and a high level of quality control can be realised. The modern use of modular construction for permanent buildings should be differentiated from the wide range of temporary buildings that are designed to lower standards commensurate with their cost and use.
This publication offers guidance to architects, specifiers and clients on the type of buildings that may be appropriate for modular construction using light steel framing. It provides broad information on the design and application of modular or volumetric construction in general building construction. It is intended that designs involving modular construction will be developed further in consultation with appropriate manufacturers. This guide is a sister publication to Building design using cold formed steel sections: An architects’ guide (1) , and it addresses: the history and main applications of modular construction in general building construction, including overseas uses the current use of light steel framing in modular construction the manufacturers of modular units in the UK, their products and recent projects the broad cost-benefit assessment of the benefits of modular construction general technical information that is appropriate at the scheme design stage guidance on planning and execution of projects involving modular units opportunities for modular construction in renovation. It does not address: temporary buildings or transportable units such as site huts and kiosks detailed technical aspects of the design of modular units other forms of modular construction in timber or concrete. The SCI publication Design of structures using cold formed steel sections (2) describes the structural aspects of the use of light steel framing, and it is not the purpose of this guide to repeat this information. However, the main technical aspects of the use of light steel framing relevant to modular construction are covered here. A wide range of projects using modular construction is illustrated in a series of Case Studies (3) published separately by the SCI. Contact details of manufacturers of modular units for permanent buildings are given in Section 13. More detailed design and cost information can be obtained from the manufacturers. An architect’s check-list of questions to be asked in discussion with the modular supplier at various stages of the project is presented on pages 92 to 94 at the rear of the publication.
The client has an important role to play in the decision-making process in relation to the use of modular construction in part or as whole ‘building blocks’. The following ‘check-list’ identified those aspects that should be considered first at the client briefing stage and later at the concept stage of the building design: Modular construction is the fastest construction technique on site, leading to business-related benefits to the client. Cellular buildings lend themselves to modular construction. Transport restrictions limit sensible module widths to 4.3 m. Economies can be lost if there are a large number of non-standard units. Modularisation of highly serviced components should be considered, even if the whole building is constructed more traditionally (see Section 8.3). Examples are toilet/bathrooms, and plant rooms. A close working relationship between the manufacturer and designer is important in the concept design, and later with the general contractor in the final design. The logistics of transportation, just-in-time delivery, and site installation should be considered in the briefing and planning stages. Local site and planning constraints encourage consideration of modular construction. Key design decisions as to the use of modular construction should be made early in the design process. The use of pre-production prototypes can help to resolve any design and production issues. The ‘lead-in’ time to manufacture of the modular units can be 8 to 12 weeks depending on the repetition of use of the modular units (see Section 8.2). Buildings of modular form can be extended and relocated as client demand changes. These and other benefits of modular construction are reviewed in more detail in Sections 2.5 and 8.
In contrast to the startling growth and technical advances witnessed this century in many industries, progress in the building industry, particularly the improvements in productivity and technology, has generally been relatively slow. An exception has been the emergence and growth of modular building methods. Ideas of factory-made housing developed in the late 1920s and 1930s; in Germany through architects such as Peter Behrens and Walter Gropius and in the USA through Richard Neutra and Buckminster Fuller. Mass production of motor cars led to similar concepts for housing, starting firstly with panel or component-based systems and later extending to modular or volumetric units. In the USA, the modular industry originated with the travel trailer (caravan) industry and increased in the Second World War as trailers became homes for thousands of defence workers. After the War, severe housing shortages created a demand for trailers as permanent housing. The industry responded by developing what are now called mobile homes, with designs that tried to strike a balance between the functions of house and vehicle. The relatively low cost of starting a factory in the early 1950s, when demand was strong, encouraged the formation of many new companies in the USA. In 1959, there were 268 manufacturers with 327 plants. By 1963, the companies producing manufactured housing had split into two distinct groups - mobile home producers and modular home producers. In 1955, plants could be started for as little as $15,000. By 1966, the average start-up costs had risen to $150,000. However, they were very low compared to the start-up costs of other manufacturing industries, and remain so to this day. Many companies have folded as a result of economic recession, and there are now 34 companies in the USA producing modular units from 173 plants. In general building applications, the use of various module types owes its origins to progressive architects and designers who developed prefabricated components, such as ‘pod’ bathrooms. The idea of the bathroom pod has been around since at least 1937, when the American engineer/inventor Buckminster Fuller developed the steel prefabricated Dymaxion bathroom. Thirty years later, Nicholas Grimshaw produced a spiralling cluster of bathroom pods in a circular tower attached to a student hostel in London. In 1978 he used similar stainless steel toilet modules - suitable for mass production - and installed prototypes in his Advance factory units in Warrington, UK. Several years later, perhaps influenced by Grimshaw’s toilet modules, Sir Norman Foster used steel toilet modules in his Hong Kong Shanghai Bank headquarters in Hong Kong. The wide publicity this building attracted played a major part in helping architects to understand the advantages of using service modules in office buildings; modular building techniques lead to improved speed and quality.
During the office building boom of the 1980s in central London, where labour and logistical problems made life particularly difficult for contractors, many major office developments (e.g. Broadgate) made extensive use of toilet and plant room modules. Proposals were made for completely modulising the core areas (a concept known at the time as total core ‘TC’) of major new office buildings. However, before those ideas could be implemented, the building boom was over, and they were shelved temporarily. A building that came closest to achieving total core was No. 22 Old Bailey in the City of London, where steel toilet modules, modular plant rooms, and modular lift shafts were used together for the first time. There has been a consistent growth in the use of bathroom pods for hotels, hostels, halls of residence etc. The larger hotel chains in Britain often specify bathroom pods for new hotel bedrooms, and for hotel extensions. It is worth mentioning that in most modern cruise ships, all classes of cabins either include toilet pods or are made as cabin pods with integral bathrooms, and that several manufacturers who make marine pods have built on that success and moved into the manufacture of modular products for the building industry.
A common characteristic of the various types of pod mentioned above is that they are all inserted into other load-bearing structures and therefore only need to be self-supporting. The highest loads are encountered when they are being handled or transported. Another characteristic of those module types is that the envelopes of the modules are generally designed to be as strong, lightweight, and economical as possible i.e. ideal candidates for the use of light steel framing. The use of modular construction in housing has been relatively slow in all countries except Japan (see Section 4.2). Modular construction has attracted considerable attention from architects who were inspired by the opportunities of the construction technique and were not over-awed by the dimensional discipline that it imposed. Modular construction also introduced the benefits of ‘mass production’ to the construction sector, but self-evidently required a large market to lead to economies of scale. In the UK, one of the first examples of modular housing construction using steel framing was in local authority (former GLC) housing in Hackney, London. At the time of writing, the housing association, Peabody Trust was constructing a major housing development also in Hackney, which was based on an extension of the now well established use of modular units in hotels.
The type of material used for the structures of modules was frequently determined by the type of product that a company produced before becoming involved in manufacturing modular buildings. Module manufacturers that were originally involved in the production of timber frame houses, not surprisingly, prefer to make their modules from timber, while companies with a background in the production of heavier structures prefer steel as their medium. The companies that have switched to light steel framing have been motivated to do so because of the need to use a material that is consistent in quality and is well suited to efficient manufacturing processes and assembly operations. In other European countries, the development in the use of modular construction has been relatively slow, and is often more associated with discrete architectural opportunities provided by the construction medium rather than a production-oriented market demand. However, a niche market in Scandinavia is in the renovation sector where modular units are used to renovate and extend existing tall concrete panel or masonry residential buildings of the 1960s (see Sections 3.4 and 11).
There are three basic types of module using light steel framing or sheeting, namely: Structural modules , which function as a load-bearing steel frame, a stressed skin box or combinations of the two functions. The modules can be stacked to produce multi-storey buildings or may be combined with primary structural frames, particularly in heavily loaded applications. Non-structural modules , which are supported by a structural frame or on a concrete floor. These modules can be located between the primary structural members. Various examples are reviewed in Section 2.3. Shutter modules , in which the steel modules act as permanent formwork for in-situ concrete. The applied loads are carried by the concrete cross-walls and floor slabs in the same way that they would be in aconventionally constructed concrete building. The light steel structure supports the loads during construction. The detailed design of structural and non-structural modules is presented in Section 7. The shutter module system is site intensive and is not widely used currently.
Various forms of other modular components have been used in major building projects. These modular units exploit the benefits of speed of construction by taking more complex parts of the construction programme off the ‘critical path’. Lifts: The time it takes to install conventional lifts will usually determine when a building is handed over to the client. Modular lift installation methods have been in use for over 10 years, and allow lifts to be installed and commissioned quickly. Modular lift shafts can be fully integrated with the structure and can be designed to provide wind bracing, or they can be free standing elements. Stairs: Prefabricated stairs are quick and easy to install, and are immediately available for use by the erection team and other building workers. Prefabricated steel stairs are usually erected as storey-high units and have been used for over 15 years in traditional steel framed construction. They are installed with protection to finished surfaces, or in a partially finished state that can be finished later. Corridors: In some systems single hotel modules consist of two bedrooms each side of a corridor. Alternatively, bedrooms may be produced as separate modules. In this case, corridor units are created from floor panels that bridge between the modules. With this arrangement, the corridor can accommodate construction tolerances. Plant rooms: The advantages and the limitations of M & E plant modules are well known and appreciated by service engineers, particularly those specialising in the design of large commercial buildings. In these applications, air handling and cooling plant can be installed by lifting onto the roof of buildings in modular units. Toilet modules: Toilet modules can be constructed as self-supporting units and lifted and slid into place on the floor of buildings. Clearly, the floor of the toilet modules will be higher than that of the adjacent floor unless a raised access floor or other covering is provided.
Production efficiency and logistics, such as transport and crane costs, play an important role in determining the economic viability of modular building projects. The following points are relevant to these issues: Ease of manufacture: Modules may not be as efficient structurally as they could be because of the need for an integrated assembly-line production and the requirements of the transportation and erection process. The way in which modules are assembled and fitted out in the factory, and lifted and assembled on site, frequently requires special components. However, there is also a need to minimise the number of components for production efficiency and to avoid unnecessary stocking. Value per unit volume: The higher the value of the modular units per unit volume, the greater the distances over which modules can be transported and used competitively. It follows that the design of modules should be such that their value/size ratio is optimised to keep transport and installation costs at acceptable levels. Often the most highly serviced elements of the building are constructed from modular units and the remainder of the structure is constructed conventionally. Finishing: Modules can be finished internally using ‘dry-lining’ techniques. Other methods may be more economic if they reduce assembly line costs. Transportation: Delivery costs depend on travel distance from the factory to the site. To avoid problems arising from road transport width restrictions, modules should not exceed 4.2 m in width or 18 m in length. Whenever possible, modules, or parts of modules, should be sized so that they fit onto standard 20 ft (6.1 m) or 40 ft (12.2 m) long lorry trailers. Erection: The larger and heavier the modules, the larger the crane needed to handle them. Also, the crane will require more space in which to operate. However, large rooms can be constructed from small modular units although additional bracing is required on the open faces of the modules to provide stability during lifting. Site logistics: The modular units are generally lifted straight from the lorry into their final position. It is self-evident that they should arrive on site at the right time and in the right sequence. In inner cities, road restrictions are often such that delivery and erection has to be done outside normal working hours. However, the operation is relatively quiet and does not involve significant waste on site (i.e. lower waste removal costs and less disruption).
The following general advantages may be attributed to modular construction using light steel framing: Short build times: Typically 50-60% less than for the equivalent conventionally constructed buildings. However, longer procurement times may be required before construction starts on site. Superior quality: Achieved by factory-based quality control methods and standards. Steel is a reliable quality assured material. Economy: Efficient manufacturing processes, fixed prices and earlier completions (leading to early return on capital). Low weight: Modular construction is about 30% of the weight of conventional masonry construction, leading to reduced foundation costs. Modular construction is ideally suited to roof-top extensions to avoid overloading the existing building. Dimensional accuracy: Small tolerances can be achieved and maintained within the module interior and in the sizing and positioning of openings. This leads to ease and accuracy of fit-out in a production environment. Environmentally less sensitive: Efficient factory production techniques are much less wasteful and disruptive on site than traditional construction operations. Seismic properties: Steel modules have excellent robustness, which usually means that they can meet international seismic standards (with relatively minor modifications). Relocatability: Buildings made from steel modules can easily be disassembled and modules can be relocated to create new buildings quickly and economically. Innovative funding potential: The ability to recover and recycle modules quickly and easily provides scope for modules to be made available to users on terms that are not possible for conventional buildings (e.g. product lease or hire purchase). Use on infill sites: Modules are useful in small urban infill sites, particularly where it is uneconomical to build because of problems of disturbance and site location. Reduced site labour requirement: The erector and finishing teams who install and complete modular buildings involve fewer workers on site than traditional buildings. Improved manufacturing skills: The way modules are made means that work in the factory and on site is reduced and greatly simplified, by advanced manufacturing techniques. Safer construction: Modular construction sites have proved to be significantly safer than traditional sites because of the more controlled operations. Component interchangeability: Standardised components, jointing details and the use of assembly jigs means that module components using light steel framing are readily interchangeable. Adaptability or extendability: Adding modules to, or removing modules from, modular buildings is typically a very rapid and straightforward process that involves the minimum of disruption to the operations of adjacent buildings. Mobility: Modules are designed to be transported easily and can be exported (subject to sensible transportation costs). Reduced professional fees: Standardised design details for modular buildings simplify and reduce the need for specialist design input. Accurate costs can be obtained from the manufacturer. Design flexibility: Steel modules can be grouped vertically and horizontally with good load resistance. The above list is not exhaustive and new advantages of using modular construction are constantly emerging.
The 1998 DETR Egan Report ‘Rethinking construction’ (5) called for a culture of cooperation and greater innovation in procurement, design and construction, leading to demonstrable savings and benefits to clients and to society at large. Earlier, Sir Michael Latham said ‘In a rapidly changing environment, both clients and the supply side are increasingly looking to improve performance and reduce and hopefully, eliminate conflict and disputes through
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