MODERN METHOD OF CONSTRUCTION TECHNOLGY
MMC is a term used to describe a number of construction methods which differ from ‘traditional’ construction. Other terms that are commonly used include off-site construction, factory-built, industrialised or system building and pre-fabrication.
Construction history is thus key to understanding and dating structures. If you can show that a particular technique was used in a certain period, then you can use that information to date a building or construction or subsequent additions to a building. As most buildings are added to over time, being able to show when changes were made is fundamental to understanding how old and how significant they are.
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Allied to our understanding of the role and conditions of those who worked on building sites, construction history seeks to understand how people in the past thought about building technology itself. How did they calculate whether something would stand up? How did they set out buildings on the ground? Here there is a clear overlap with the history of engineering and the building professionals, including the roles of overseers, designers, architects and engineers in every period.
Construction History encompasses all periods from the various earliest signs of human activity to the very recent past, from cave dwellings to nuclear power stations. Obviously the techniques used to study these periods vary. Early buildings lack written records, so the descriptions tend to depend entirely on archaeological recording and interpretation. Later, written records can be used along with archaeological recording. In more recent periods very details accounts may survive, with drawings, models and photographs to show how building were put together and oral histories can be compiled from those who worked on them
Prefabricated housing has been used in the UK duringperiods of high demand, such as after the World Warsand during the slum clearances of the 1960s. In totalabout 1 million prefabricated homes were built duringthe 20th century, many of which were designed to betemporary. However, problems arose over the quality ofbuilding materials and poor workmanship, leading to negative public attitudes towards prefabrication.
Nevertheless it has continued to be used in the UK forhospitals, hotels and schools, as well as for housing inother countries. MMC is a new term intended to reflect technical improvements in prefabrication, encompassinga range of on and off-site construction method
1.nhbcfoundation:to examine current attitudes ,policies ansd use of mmc and its prospects for future,the NHBC foundation commissioned research amongst large and medium sized hose builders and large and medium size housing association in private and social residential sectors
The research set out to answer the following question
- The extent to which organisationareembracinfg or considering mmc
- Factors which are driving their interest
- Reason for usinfg or rejecting mmc
- Benefits and drawbacks experirnced I use
2.the research undertaken by BRE shows the houses to be more energy efficient , on the contrary there was no evidence of transport and waste reduction
Types of mmc:
1: volumetric construction: three dimensional units produced in factory fully fitted out and dropped onto foundation to form a structure e.g bathroom or kitchen
2: panelised construction: unit produced in factory and than assembled into three dimensional in field e.g concrete wall panels,curtain walling etc.
3: hybrid construction: volumetric construction integrated with panelised construction
ADVANTAGES OF MMC:
• Economic – MMC houses typically have fewer defectsand can be built more quickly.
• Environmental – the houses can be more energyefficient, may involve less transport of materials, and produce less waste.
• Social – there may be fewer accidents and less impacton local residents during construction.
Current use of MMC
The majority of homes in the UK are still constructedusing traditional ‘brick and block’ masonry. However,within the last few years there has been increased use ofMMC for housing, driven by a range of factors includingdemands for faster construction and skills shortages.There is uncertainty about the amount of MMC housing2being built. A few large private house builders haverecently invested in MMC factories so production willincrease. It is estimated by the National House BuildingCouncil that about 10% of new UK homes are built usingtimber frames, and 5% using other MMC; equivalent toabout 25,000 MMC homes per year. There aredifferences within the UK, most notably in Scotland, where timber frames have long been preferred,
International use of MMC:
In Japan 40% of new housing uses MMC. In other Europeancountries there is also much greater use of MMC,particularly in Scandinavia and Germany. Indeed, somehouse building companies in Europe have started to exporttheir houses to the UK; for example, one UK HousingAssociation is importing modules from Poland.The reasons for greater use of MMC in these countries are uncertain, but suggestions have included:
• in colder climates the building season is short due tobad weather – use of MMC allows quick construction.
• MMC building materials, such as timber, are morereadily available.
• there is a greater tradition of self build housing. MMCappeals because faster construction reduces disruptionto neighbours and allows earlier occupancy.
• there are cultural preferences for certain house styles,e.g. timber frame in Scandinavia.
While the Government is keen to encourage use of MMCfor house building, research is still ongoing to assess itsbenefits. Issues arise over the cost of MMC; the industrycapacity; its environmental benefits; the quality of suchhousing; public acceptance; and planning and buildingregulations. These questions are considered below.
Although some house builders argue that MMC is lessexpensive than traditional methods, industry sourcesindicate increased costs of around 7-10%. Reasons forthe higher costs are difficult to discern because mostproject financial information is commercially confidential, and traditional masonry building costs vary widely too. Itmay be that the costs appear high because some benefits of using MMC, such as better quality housing and feweraccidents, are not obviously reflected in project accounts.MMC housing is faster to build, reducing on-siteconstruction time by up to 50%, and thus reducinglabour costs. Quicker construction is an extra benefit forbuilders of apartments (because viewing often starts onlyonce all flats are finished), and for Housing Associations, who receive rent earlier. However, it is less important forprivate house builders as they rarely sell all the properties on a new development at once.An additional consideration is that the majority of factoryoverhead costs, e.g. labour, are fixed regardless ofoutput. In contrast, site-based construction costs are only incurred if building is taking place. It is therefore lesseasy with MMC to respond to fluctuating demand.
Industry capacity may be a barrier to increasing thenumber of houses built using MMC. Difficulties fall intotwo categories: a shortage of skills, and the factory
There is a shortage of skilled labour in the UKconstruction industry, with over 80% of house builders reporting difficulties with recruitment. Using MMC tobuild house parts in factories, and faster on-site construction, means that fewer labourers are required.Factory workers with previous experience in othersectors, such as the car industry, can also be used.However, there is uncertainty about the level of skillsneeded for MMC compared with masonry construction.MMC can require highly skilled labour for precise on-siteassembly of factory-made house parts. Some of theproblems with prefabricated housing built during the 20thcentury stemmed from poor skills, rather than defectswith the housing materials. The Construction IndustryTraining Board (known as CITB ConstructionSkills),funded by industry and Government, is developing MMCtraining courses for the estimated 2,000 workers erecting
MMC housing with no formal qualifications. Governmenthas also suggested a need for training for other industry professionals, including surveyors, mortgage lenders, and planners, to ensure they are fully aware of MMC.
There are currently over 30 house building factories in the UK. A recent survey found there iscurrent industry capacity to produce over 30,000 MMChomes per year.5 Therefore existing factory capacity should be sufficient to produce about 17% of new UKhousing, based on a current building rate of 175,000homes per year. Production could be increased byimplementing more factory shifts.
The Government is promoting the environmental benefits of MMC, as are many of the manufacturers. Research conducted by the Building Research Establishment (BRE) found MMC homes to be more energy efficient, but there was no significant evidence of waste and transportreductions. Evaluating the environmental benefits of a new MMC housing development is complex because it is difficult to attribute outcomes solely to the use of MMC
Houses built using MMC typically require less energy toheat because of increased levels of insulation fitted in thewalls and roof, and also less air leakage from thebuilding. One of the reasons house builders are interestedin MMC is because they anticipate that the energyrequirements of the UK building regulations will soonbecome more stringent. The 2003 Energy White Paper committed the Government to implementing new energy related building regulations by 2005.
Construction and demolition waste comprises 25% of UK waste. The amount of waste produced using MMC islikely to be reduced because factory materials can beordered to exact specifications, and there is a lower riskof on-site spoilage, e.g. through wet weather. However,there is little research confirming such reductions.
Building homes in factories may reduce the total numberof trips to a building site. This is of growing importanceas more house building takes place on ‘brownfield’ sitesin inner-city areas. Little detailed analysis has beenconducted to date on transport benefits, but they arelikely to vary considerably depending on the distancebetween the building site and the factory.
Quality and accreditation:
The number of defects in traditionally built homes in theUK is considerable, with house builders allocating up to£2,000 per house to rectify problems. Greater use offactory production can reduce defects because there isless risk of weather damage during construction, andmaterials can more easily be standardised and tested.However, if there is belatedly found to be a problem with
a particular MMC then this would have been replicated inmany homes, because they are mass produced. Housingis built to last a minimum of 60 years, so problems couldgo unnoticed for some time. For this reason buildinginsurers, mortgage lenders, and surveyors are cautious about greater use of MMC. For example, some insurersare worried about the resilience of MMC to flooding. Incontrast, the risks of traditional site-based masonryconstruction are well known because the method has
been used for a long time.Accreditation systems to test the performance of housingproducts are operated by the British Board of Agrément7and BRE Certification. But the process can take over a
year and cost up to £100,000, meaning that not allcompanies apply. Six housing MMC have been grantedaccreditation so far, with three more in the pipeline. Ifhouses are built using unaccredited methods then it canbe difficult to gain buildings insurance, and hence amortgage. Some manufacturers argue that Governmentshould offer grants to assist with accreditation.The Council of Mortgage Lenders suggests that theHousing Corporation should make it mandatory to useaccredited methods when building social housing. TheHousing Corporation is reluctant to do so because itbelieves the decision about which MMC to use should betaken by individual Housing Associations. Also, with the 25% MMC target commencing in 2004, there areconcerns that there would be insufficient industry capacity if Housing Associations were limited to usingaccredited manufacturers. Government and industrybodies are in preliminary discussions about options for a’fast-track’ accreditation scheme.
There are industry concerns about the publicacceptability of MMC housing. A survey of MMCmanufacturers identified lack of market demand andpublic perception as the two most important limitationson expansion.5 Industry concerns reflect public opinion:in a 2001 MORI poll, 69% of respondents felt a brickbuilt home would fetch a better price.8 Negative attitudestowards MMC may stem from highly publicised problemswith historical use of prefabricated housing. There arealso concerns that if more innovative MMC is usedexclusively for social housing the distinctive design may mean residents are stigmatised. However, all but onetenant of a new social housing MMC development inLondon said they would be willing to buy a similar home.Also, because most UK MMC developments are made tolook like traditional brick houses, potential occupant may be unaware of the construction method.
The planning system has an important indirect influenceon the MMC market because of its role in determiningthe supply of land for house building. Governmentplanning policy is laid down in Planning Policy Guidance(PPG), one of which (PPG3) is about housing. PPG3covers issues such as housing density, but use of MMC isnot currently mentioned, and planning guidance wouldnot generally cover such details about construction type.
The UK building regulations do not specify buildingmaterials or construction method, but instead set minimum performance standards. Proposed changes tothe building regulations covering energy efficiency,broadband access and structural integrity areforthcoming. These changes may make it cheaper andeasier for MMC to meet the regulations compared withtraditional masonry construction.
Health and safety:
The construction industry is one of the most dangerousfor workers, with about 100 deaths per year in the UK.MMC could improve safety because there is a reducedrisk of accidents in a controlled factory environment, andless time is spent on the construction site. The Healthand Safety Executive, who regulate construction safety,are encouraging the use of MMC.
EXAMPLES OF MMC:
Zurich Municipal’s definition is: A construction process that can encompass the use of composite new and traditional materials and components often with extensive factory produced sub-assembly sections. This may be in combination with accelerated on-site assembly methods and often to the exclusion of many of the construction industry traditional trades. The process includes new buildings and retrofitting, repair and extension of existing buildings. Identified below are examples of more common types of MMC: 1. Super-structure
- Modular Construction
- Pod Construction
- Open panel – Timber frame and Steel frame
- Structural Insulated Panels
- Solid Cross Laminated Timber Panels 2. On-site technologies
- Insulated Concrete Formwork (ICF)
- External Finishing Systems
- Timber Cladding
- External Finishing Systems (EIFS)
- Brick Slip System
- Green Wall and Roofs
For new build developments using Modern Methods of Construction evaluating the following areas and implementing controls will help ensure a successful build:
- Build quality control e.g. adequacy of inspection regimes during the build
- Selection and competency criteria for contractors
- Standards for construction site fire safety
- Standards for construction site security
- Compliance with published safety guidance e.g. trade associations, Health and Safety Executive (HSE) or insurer recommendations
- Emergency procedures
Reducing risk at the design phase is an important component in the delivery of a successful build. Ensuring all stakeholders are engaged in reducing risk ultimately adds value by ensuring potential losses can be minimised as well as more subtle benefits through reduced maintenance costs, improved occupier satisfaction and well-being. An example of reducing risk for wall construction is given below but the principle of reducing risk should be applied across all elements of the design. The wall or facade of the building can have a material impact upon the arson or accidental fire risk. It can also affect the fire spread risk should a fire occur and ultimately the extent of any loss. Within the social housing sector there continues to be a demand for Modern Methods of Construction (MMC). MMC can offer advantages such as improved build time, environmental benefits and reduced on-site labour costs. The extent of these benefits often depends upon the size of development and design employ
Pros and Cons of Modular Construction
- Thanks to the ability for the project to run simultaneously on-site and in-factory, modular construction can be up to 50% quicker than traditional construction.
- As major parts of construction are handled within a factory, weather conditions are often irrelevant during the majority of the project.
- The factory-based manufacturing process allows not only for greater quality control during the manufacturing process but for many health and safety risks to be considerably reduced, if not eliminated,
- The process aims to minimise waste and reduce the project’s carbon footprint, as fewer people are travelling to the site and modules are produced directly to spec using Computer Aided Manufacturing.
- The impact on the community surrounding the construction site can be significantly reduced, due to much lower levels of noise and traffic during the project period
- The methods employed in modular construction can often benefit the energy efficiency and airtightness of the final construction
- Access to the site must be considered from the very beginning, as it will need to allow for the delivery of large modules.
- Traditional construction allows for later design changes, while modular construction is unlikely to be able to factor these in, so early complete design sign off is crucial with clients.
- The logistics and planning of individual module assembly will need rigorous planning to ensure a smooth project.
WHY MODERN METHODS OF CONSTRUCTION OUTPERFORMS TRADITIONAL CONSTRUCTION AT EVERY LEVEL:
following are the reasons:
1) they are manufactured in less time.
2) they are well designed in a control environment.
3) as they are designed in a controlled environment, there are very low chances of errors and quality compromise.
4) they are cheap as compared to traditional methods.
5) due to rapid demand of infratructure.it is the future of construction industry.
6) less labour is required.
7) it is easily assembled and can be easily re-assembled.
8) it offers greator choice and adaptability.
9) it is very economical and efficient method
In short mmc is very good to be adopted because it reduces times and save energy secondly the structure is very efficient rather by adopting old cultural techniques.In most of developing country is mmc is adopted like in England,china,japan,America etc.
In modern method of construction structure can easily be placed and removed when new changes are required but skilled labour is needed for operation.
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