This report was written as a result of the accumulated information available on the enhancement of building construction. I am convinced that there was a need for a report that covered the principles which were involved in offsite manufacturing which could ensure that all readers had a good understanding of the importance of the subject for future developments.
The aim of the report was to be able to get an understanding of the subject and to fully understand the emerging advances which will occur in offsite- manufacturing within the UK.
The method is to introduce the background of offsite manufacturing, including and brief analysis of each system, with analysis of the applications of which these methods can be applied to e.g. student accommodation and hospitals. Also the benefits of the different systems being applied to applications has be analysed, to conclude an outcome of the future advances in offsite manufacturing for humanity. Linking the benefits which have been researched to other matters such as house prices being predicted to rise from 2012-2014, where house builders, developers etc are keen to develop and constructing before the predicated date at a smaller cost and time scale, achieving higher quality construction. It would achieve a more financial benefit than normal from house prices rising, when the house price rising period has been proven. Included is an investigation using case studies of developments which have used OSM systems, which has helped to support the research for the emerging advances.
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The reason behind this study is to conclude what we within the UK can expect to see for the near future of building construction and technology, and emerging advances in Offsite Manufacturing. As recent house prices within the market are being predicted to have a rise from 2012, with demand, activity and prices, the activity during 2012-2014 should be probable to a rise, encouraging increased participation by house builders, developers, lenders and investors.
The concept of OSM
Offsite manufacture or construction refers to building structures being built not at the location of use but at a different location, which occurs in a specifically designed manufacturing warehouse or plant. This sort of process manufactures parts or modules of the building which is at first constructed in the factory then transported on specially designed trailers to the site. Once on site, the building is installed on permanent concrete foundations, which are already positioned before delivery of prefabricated parts. These buildings meet all applicable building regulations and are indistinguishable from onsite construction
The volumetric technique uses units which are three dimensional modules that are prefabricated in a factory environment, with the leading market being of either a closed module design bathroom pods or units suitable for student accommodation etc of a one bedroom layout being used continuously. There are also open sided module units which are also used that allow deeper plan buildings to be constructed, but offer less opportunities for developing upon technical details. The benefit achieved from using a volumetric approach is being able to make highly serviced areas within factory conditions. More than 30 trade activities are transferred off-site, leading to fewer people on site, easier commissioning and less rework. (Langdon & Everest, 2004 issue 42). The cost of the project usually depends on volume and complexity, but also for specialist applications which can be of a limited production number the costs can be exceeded. Whereas, if the production where to be of larger volumes of repetitive works, then the cost of the project can be reduced slightly. Resulting in the more you want of the same thing, the cheaper it can be.
The Panellised technique consists of flat panel walls, floors and roofs which are prefabricated off site and assembled on site. There are different materials used within the range of different systems which are used, consisting of timber frames and light steel frames which are open without insulation being fitted, also factory finished units which have insulation, windows, doors and services installed are used.
The main market for panellised systems is residential construction, where in England and Wales, timber frame has a 5% share, much lower than in Scotland and other European countries. (Langdon & Everest, 2004 issue 42) With the evidence that residential construction in England and Wales has a low share of timber frame usage, and with England covering the majority of the UK, its demonstrates that the majority of the UK doesn't use enough panellised systems. Timber panels typically add a capital cost premium of up to 5% that can be recouped via savings from reduced defects and rework in a well-managed site. (Langdon & Everest, 2004 issue 42) So with this in mind the more expensive it may seem to prepare and erect the panellised system, there saving will be noticeable slightly before and after the completion of the building.
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There being many advantages of using panellised systems, such as the speed, weather impact, and flexibility of size, and with the integration of latest software's and manufacturing machinery within the factory used today, it allows a curtain amount of customisation to be achieved, which allows the demands of clients to be more flexible rather than being limited.
The Hybrid techniques use parts from both other systems, using different advantages such as using the module technique for the serviced areas which come from a high quality fitment and others from panellised which allow that approach of flexibility for other areas which are needed. The full hybrid solution is relatively rare (Langdon & Everest, 2004 issue 42) and this can be expected as these single technique along are financially expensive to start up, and to join the both systems into one more complex and larger service, it is able to see that a larger factory working space would be required for the prefabrication stages.
Introduction to the Latest Advances of OSM and the application to housing in the UK
As we have witnessed from studying architectural technology, that there has been recently the increased focus of greener design strategies in building, people of today are now becoming more active with the taking part of helping the environment for a greener one. With many issues of sustainability being a main focus, people are protecting the natural resources we have remaining to improve our environments. Following from this is the advances in the use of OSM and the use of implementing sustainable feature which are added within the factory, under better workable conditions with regards to weather and waste.
The cycle of innovation in alternative systems using renewable and recyclable materials and energy are everywhere. (Kaufmann & Remick, 2009) The focus on using sustainable strategies within the building industry, has led to an advance of the materials we use, take for example the Apple iphone being one of the leading mobile phones of today. it no longer uses the ethical approach of a bigger phone is a better one, its changed that approach with the evolving humanity, making a mobile phone that you can do more with, which is better. It is now part of a broader cultural conversation about how to do more with less. (Kaufmann & Remick, 2009)
Compared with the building industry, now the methods of construction we choose to take has changed also, taking away problems which may occur onsite such as waste, less labour hours and sustainable features, allowing many savings within different aspects.
There is a high demand at the moment from markets which are successful such as hotels and student accommodation which are demanding work at almost maximum capacity for the volumetric approach, compared to the growth of the panellised technique which has not had such an increase in demand.
... a 25% modern methods quota for homes funded under the Housing Corporation's Approved Development Programme, demand for panelled systems is likely to increase as it is the simplest option for Housing Associations to implement. (Langdon & Everest, 2004 issue 42)
With this is mind the capacity of the panellised technique should increase due to the increased demand made by the Housing Corporation's Approved Development Programme. Considering the flexibility of the panellised technique, it is used more often for the application to housing for customisation of design, rather than being repetitive like the volumetric approach.
Current use of OSM
With most homes in the UK being still constructed using traditional methods of construction, there has been an increase in OSM for housing. The "Parliamentary Office of Science and Technology" report that about 10% of new UK homes are built using timber frames, and 5% using other MMC; equivalent to about 25,000 MMC homes per year (Parliamental Office of Science and Technology, December 2003). There is more timber frame used within Scotland compared to the rest of the UK as this technique is easier to come across in that country as its preferred more.
Techniques emerging for OSM and there relation to housing
With environmental issues still concerning the people of today, and developers starting to recognize that it would be beneficial to use sustainable methods of prefabricated architecture, benefits such as shorter time scales, better predictable costs, lower risk issues, and government incentives, leads to sustainable practice and products to increase and to be used for our environments.
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Current housing seen from history shows the effects of which they have on the environment and of the land they use. Sustainable design is the approach needed to create healthier environments which needs to be implementing within prefabrication for further savings. With there being emerging techniques for OSM evolving with time, there can be rough predictions of what technology are at hand for use in the near future.
At the moment there are many techniques being introduced but only such are actually being used, these systems and techniques are listed and discussed below:
SIPS (structural insulated panel systems)
A recent techniques used involves structural insulated panel systems (SIPS), where insulation core is bonded to sheet board to form a panel, creating a composite building material. They consist of a sandwich of two layers of structural boarding with an insulating layer of foam board in between. SIPS involve similar structural properties as the I beam.
An eco hub is a new technique of multi housing, where they are used to power a community rather than being on a single house, which would produce a better environment. Instead of fixing a number of solar panels or wind turbines, which would depend on the orientation of the house, they may not be fitted to the best effect possible. if the house was built at a better thought orientation with the other houses of the new build community, the environmental technologies could be allocated within a shared community space.
Steel homes are also alleged to be good for allergy sufferers, utilising none of the resins, adhesives and chemicals used in other construction techniques. (kit homes: eco friendly, 2008). Not necessary a new technique, but it utilizes the previous success of using steel to create stronger structures such as high rise buildings. Steel is different to wood and other materials, as it can last for a considerable amount of time longer. Steel frame kit homes will stay in the exact same shape as the day it was built (Benefits of using steel frame kit homes, 2009) compared to timber framed structure which over time, twist, bend and move from weathering and ground movement. There is also the interest in using steel framed systems as it has a certain amount of fire resistance more than other materials and it prevents the infestation of beetle infection, which results in the long run saving which can be achieved.
Low carbon achievements
As manufacturers are now starting to use OSM, and the enforcement of the Code for Sustainable Homes has been introduced, the manufacturers are combining the two issues of prefabrication with sustainable feature. Let alone that fabricating offsite achieves sustainable aspects for lower waste produced, lower disturbance and transportation, it's a concern to implement further sustainable features of recycled materials and sustainable technologies such as solar panels and photovoltaic panels.
Comparison of Prefab and On-site for housing
A comparison of prefabrication and onsite construction has been introduced as it can help to conclude the advantages and disadvantages for housing developments and developers.
Process plans which have been prepared by the Salford Centre for Research and innovation (Table 1) shows the difference in change for different construction techniques, with comparison to the time for activities, when workers are needed to arrive on site, and other resources such as time acquired for the use of scaffolding.
Table 1: Comparison of different construction methods that have different requirements
Brick and Block
Open panel/Advanced panel/ hybrid
Brick layers on-site Arrival of first following trades Scaffolding in use 44 days 16 weeks after groundbreak 11 weeks 20 days 7 weeks after groundbreak 8 weeks 20 days Not used 6 weeks
Source: Process plans prepared for the National Audit Office by the Salford Centre for Research and Innovation
The table above from the process plans are of a example developments of 22 dwellings, where bricklayers would be required to construct a brick and block structured dwelling.
It clearly shows that the bricklayers time on-site is more than half less when using the prefabricated approach compared to a traditional construction, and allowing the arrival of the first following trades to commence more than half less of time with Panellised systems, but differing with volumetric systems as the there is no need for following trade to be used after erection as the units are fitted out within the workshop with all or at least most finishes already applied. The table also demonstrates than the time of the needed use of scaffolding is reduce approximately by 3 week with panellised systems and 5 weeks for volumetric which results in lower costs for the hire of scaffolding equipment unless the manufacturers of the prefabrication have their own supply of scaffolding if they provided the service of erecting the structure with the cost of purchase.
The table above shows costs which have been calculated for a range of suppliers of each different technique within the industry. The cost average has been converted to a range of upper end and lower end quality and costs only cover the construction type of a dwelling. It clearly shows that for the traditional construction method of onsite works using brick and block techniques and open panel technique, they hold the lowest construction cost of £600-1000 per m2. As for the hybrid system, its construction cost is from $700-1100 per m2. Following then at the highest end of the cost scale is the volumetric technique which ranges from £780-1300 per m2. These results show that the traditional brick and block, and open panel systems are the most cost effective. As can be seen there is a fair amount of overlap of costs for the different methods, and the volumetric technique is the most expensive with regards to construction costs, but the consideration towards the time savings and labour saving etc must be taken into account as this will result in money savings. If in the nearby future there is potential for reduction in the price of manufactured materials and components, this could reduce of overlap of different costs. Taking into consideration than faster construction and reduced onsite work can achieve some financial benefits to the project
Source: Cost calculations prepared by the National Audit office using information provided by the Building Cost Information Service and process plans developed by the Salford Centre for Research and Innovation
The table above shows where savings are found in relation to floor area, demonstrating that financial benefits can be achieved compared to a brick and block construction, from using hybrid and volumetric systems, showing substantial savings with relation to the previous table (Table 2).
The National Audit Office report four advantages that provide financial benefits to Landlords if they were to use an OSM approach, such as earlier rent can be obtained from the date of release, Social Housing Grants can be drawn at a earlier stage, reducing interest payments on capital to fund developments, snagging costs are reduced because off-site construction elements are subject to the tighter quality control made possible in factory conditions and the need for on-site inspection decreases as the amount of off-site work increases. (National Audit Office, November 2005). With these four advantages of financial benefits from faster construction and reduce onsite work, it allows developers to become a part of a new age for OSM.
Source: Cost calculations prepared by the National Audit office by the Building Cost Information Service using process plans developed by the Salford Centre for Research and Innovation
The table above shows an increase in the proportion of costs that are incurred offsite, where there has been research undertaken to see where most costs occur and the differences, and it clearly shows a massive reduction in the time spent for on-site materials and on-site labour for the volumetric technique compared with the brick and block, with the open panel and hybrid systems sitting in between to two for a balance of both worlds. Resulting with if volumetric approaches lowered there cost of offsite manufacturing it would increase the demand and competitiveness.
Advantages & Disadvantages of prefabrication
- Self supporting components are used, so the need for formwork and scaffolding are lowered.
- The amount of time for construction is reduced and structures are finished faster, allowing an earlier return on the capital invested in the project.
- Onsite construction work and any possible congestion is minimised.
- The quality of the completed built tends to be of a better quality as the condition are less effected by weathering.
- Less waste is produced as they are manufactured in factory conditions, making it easier to recycle the waste back into another use.
- Templates can be used to replicate repetitive builds
- It is required that careful handling of components like glass and concrete panels is undertaken
- Attention to detail needs to be taken into consideration insuring the that the structure would be less likely to fail at joints
- Relating to the previous, where leaks can form at the joints if attention to detail is not taken
- Transportation for the volumetric technique can cost slightly more compared to panellised systems which can be packed more efficiently for less journeys.
- Large sections can sometimes require the hire of large crane and precision works to place into the allocated position
Main drivers for using OSM in housing
A consideration towards the main drivers for using OSM in housing relating to Modern Methods of Construction has been research, as these aspects affect the rate of which developers are using OSM within housing.
The main drivers for using OSM in housing are summarised and discussed below:
- Housing shortage
- Skills shortages
With there being a shortage in the housing market in the past, its allowed governments and some sectors of a construction industry to reconsider traditional practices. As it is hard for single people to affordable housing, they generally lead to flats as they are cheaper, which results in the government and sectors to be interested in how they are built compared to traditional methods as these are becoming more popular.
An important issue about flats is that they affect builders' cash flow in a way that houses do not. With houses, each one can be sold and occupied before others are built. With flats, the whole block will usually need to be completed before it is safe to allow occupants to move in. (IHS BRE Press, 2007)
This shows that cash flow can be a problem as potential buyers don't want to pay the full price up front, resulting in the need for quicker methods for erecting flats, such as modern methods of construction, which has that advantage of being a faster build. Also the potential buyers are generally not that concerned about how the flats were constructed as long as the structure performs to a satisfactory standard.
Skills being trained within the industry is falling behind compared to skilled workers leaving the industry. The shortfall in operatives has been at least partly compensated for by inward migration and this is particularly true for the semi-skilled and labouring grades (IHS BRE Press, 2007). Resulting in many trades being transferred offsite for continuous.
The National Consumer Satisfaction Survey reported in 2003 that the satisfaction level among purchasers of new homes was approximately 40%. (National Audit Office, November 2005). At the moment housing is overpowering with traditional construction techniques which results into needing to look into other emerging techniques. Where a house can be built with a poor quality, it can be of a poor design or it can fail to conform to that design or both. As building companies sometimes fail to conform to the design due to bad weather conditions that effect the total program. When developers use the OSM approach, they can expect to be able to conform easier as the site conditions are controlled indoors, also taking into consideration the factory machine which is used ensures high standard of quality to conform.
The amount of waste that can be produced with onsite construction, seen to be wasted money, acts as a driver for using modern methods of construction to minimise the waste, as it's within a controlled environment, insuring money savings. Costs which the developer encounters are likely to lower over a course of time as they will be more knowledgeable of the system for OSM, and allow them to develop better efficient strategies for onsite works.
Main barriers for using OSM in housing
The main barriers for using OSM in housing are summarised and discussed below:
- Lack of experience
- land in the house building process
- On site skills
- Lightweight construction overheating problem
- Site constraints
Lack of experience
With a change in the construction methods it's more difficult to find house builders with good expertise in this area or at least a house builder that can pick up the method quite easily. This can only be overcome by the use of training facilities to educate the trade enhancing their confidence.
The importance of land
The importance of land has an effect that shows why the new build industry for OSM is slow, but it can be likely to change as developers are required to conform with the Code for Sustainable Homes and results in construction onsite being slightly challenging compared to before.
Many manufacturers work hard to develop erection crews and to make sure that they are well trained and this will need to continue and expand to meet builders' concerns (IHS BRE Press, 2007). As manufacturers can expect to employ their own in-house builders to construct to the specifications of the design from that company, this may result in onsite trades being minimized, as the manufacturers will want to provide a better design and build service, to insure in positive credibility of product and service.
Lightweight construction methods such as Timber frame, SIPS and steel frame can have an effect as climate changes and summer weather gets hotter, the structures may be likely to overheating. The overheating may be resolved by shading and ventilation, it can also be resolved if the occupants of the house required rooms to cool quicker, where a structure of a low thermal mass would be acceptable.
There can be constraints which can occur when delivery of the prefabricated parts takes place as the size of the site may be limited. It can just tend to be that the sites themselves have access limitations. OSM techniques used within a constrained site can have its benefits of quicker erection which may be needed within a city centre to cause fewer disturbances.
Recycled and refurbished modular building - nursery, London docklands
There was a requirement for a new designed nursery building for the University of East London's Docklands campus which was constructed from refurbished building modules. They required a more sustainable approach to construction, a building of a higher quality construction which met the client's budgets and a calm and welcoming environment for children of a young age. It has demonstrated that there is a potential for this approach of a more environmentally friendly construction process. The client may have used this approach of construction as some sort of savings in cost, or to act environmentally towards the community as the nursery may be a government funded project. The nursery shows the use of untreated cladding which achieves a lower impact on the environment, and the structure fully complies with building regulations.
The benefits achieved are:
- it is a building that is robust, substantial and pleasant to the eye
- Completion on time scale and on limited finances
- The creation of a highly sustainable alternative for a new build and a way of lowering the building's carbon footprint
The centre has met requirements without any alterations needed to the design, and provides an attractive facility, which has been well appreciated by staff, children and parents.
Modular house - Prefabricated
There was a requirement for a structure to be built as a modern detached brick house that is completely prefabricated offsite, it responds to the principles to innovative technique and being conscious to environmental issues. The structure is a standard three bedroom family house, with the need to reduce site delays. The modular system uses heavy steel frames and solid concrete floors. The house is moved to its permanent location in four units that are installed on to ground works in a single day, allowing a fully functioning dwelling to be assembled in less than 24 hours. Site work is confined to the laying of foundations and the connecting of modules and landscaping.
The Benefits achieved are:
- Increased predictability in costs and time
- Reduction in time needed for installation
- High thermal values
- Wall heights of up to 12m achieved
Modular house Extension - Prefabricated
There was a requirement for a new extension to be added to a modern 'Art Deco' home in Cheshire, which retained the period feel of the property.
The main drivers and constraints of the project where to minimise the overall time taken in the project, with constraints from transporting the products to the site.
A steel construction method was used with a rendered exterior finish for the prefabricated extension. It was a curved roof extension, which contained a bedroom with en-suite facilities, also containing a spiral staircase. Large glass doors used to open out onto the timber deck of the existing roof. Due to the size of the required structure the module was divided into two sections after being fabricated within the factory to insure easier transportation
The Benefits achieved are:
- The prefabrication took six weeks, with all fixtures and fitting built ready into the units
- The time taken to unload and install the modules took one day, which allowed the clients to use the extension within later of the same day. Connection and interface items took an extra week to be applied
Results & Discussion
There are 3 main techniques which have been investigated such as volumetric, panellised and hybrid systems, with the benefits following being listed:
Volumetric techniques using repetitiveness allow financial savings for the developer, whereas Panellised systems main market is residential construction with a low share of timber frame usage in England and Wales which means the majority of the UK doesn't utilize enough of this technique. Also that the Hybrid technique is rarer to be used which uses the volumetric and panellised techniques combined.
The investigation found that the current use of OSM reported in 2003 shows that 10% of new UK homes use timber frames and 5% use other modern methods of construction producing approximately 25,000 MMC homes per year.
EMERGING TECHNIQUES FOR OSM
The results found show the latest emerging techniques to be used within the building industry, which is listed below:
- Structurally insulated panel systems (SIPS)
- Steel homes
- Flat pack house or kit homes
- Recycled building modules
COMPARISON RESULTS OF PREFAB AND ON-SITE CONSTRUCTION
From the comparison results of a prefabricated structure and a tradition structure that uses onsite methods more, it can be seen that the bricklayer's time needed on site is reduced and arrival of first following trades commences earlier with prefabrication, also noting that the time for Scaffolding usage is minimized.
Prefabrication or OSM can tend to be more expensive than traditional build construction, but does incorporate financial benefits compared to onsite traditional methods.
Financial benefits that can be achieved compared to onsite are:
- Earlier rent
- Shorter borrowing period
- Less snagging
- Less onsite inspection
The investigation found that benefits can also be achieved from faster construction and reduced onsite construction, brings financial benefits to developers. Also modern methods of construction tend to be more expensive compared to that of onsite traditional build.
Summary and Conclusion
The objectives of the study have been researched and concluded to achieve an understanding of the emerging advances.
Objective 1: An investigation of OSM
The research has revealed that there are three main techniques used being volumetric, panellised and hybrid, which panellised system being of the most cost effective solution for housing, but differs with the use of volumetric as they could be used in a repetitive manner for flats for example brings financial benefits.
Objective 2: an investigation of the latest advances for OSM
This research has revealed that the emerging techniques are struggling to be used today within the building industry, with SIPS being the most advanced of the majority of techniques advancing, as this system is the easiest to be applied to housing applications of today. With the introduction to "Ecohubs", its can be expected to see this technical approach to be implemented more by developer as multi housing is at an almost constant construction rate, which would benefit from using aÂ centralised area within the multi housing to associate these technologies. Flat pack housing on the other hand is driven down as it requires external skilled workers to install the kit, and as these technique are new to the industry, the skill that understand these techniques are fairly limited.
Objective 3: an investigation of OSM applied to housing in the UK
The research has revealed that panellised systems are of the most common for the use of OSM for existing buildings are they are more flexible with the application. The volumetric technique is also used for existing buildings but mostly for specific sized extensions. These extensions of the volumetric approach can be seen to be problematic with the fitment of the unit to an existing wall face of a different structure type, as these techniques may not be easily compatible as they can be different, creating problems for joints of air permeability and leaks.
Objective 4: an Investigation into the drivers and barriers of using OSM for housing.
The research has revealed that there can be potential benefits that can be achieved, but also that barriers can occur at a similar rate, so depending on the type of OSM method to be used, there costs for financial benefit can differ. For modern methods of construction to become more popular within the building industry, developers and manufacturers need to analyse there strategies to be able to overcome any possible barrier which may prevent any further development.
Bibliography & Referencing
Benefits of using steel frame kit homes. (2009). Retrieved Febuary 16, 2010, from Kit Homes nation wide pty ltd: http://www.kithomes.net.au/benefits.htm
IHS BRE Press. (2007). Modern Methods of Construction (MMC) in housing.
Kaufmann, M., & Remick, C. (2009). Prefab Green. Gibbs Smith.
kit homes: eco friendly. (2008, 10 07). Retrieved January 5, 2010, from channel 4: 4homes: http://www.channel4.com/4homes/diy-self-build/kit-houses/kit-homes-eco-friendly-08-07-10_p_1.html
Langdon, D., & Everest. (2004 issue 42). Cost Model: Off-site Manufacture. Retrieved from Building: http://www.building.co.uk/hybrid.asp?navcode=3531
National Audit Office. (November 2005). Using modern methods of construction to build homes more quickly and efficiently.
Parliamental Office of Science and Technology. (December 2003). Modern Methods of house building.