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So called "Modern Methods" of construction have been put forward as a solution for solving the problem of providing affordable housing in sustainable communities for the UK.
In a report for senior managers of a major housing development company propose and justify modern methods of construction to replace traditional construction production techniques.
There is growing concern in UK that housing is becoming more and more expensive. There are a number of concerns among experts that the construction industry as a whole is underperforming. This has been particularly emphasised in the Egan report (Egan, 1998), where it is also mentioned that the initial opportunities for improvements in house building exists in the social housing sector. Another concern that is very much in the lime light recently is sustainability issues. The European community and UK have agreed of environmental and energy targets that are very ambitious.
Houses in UK have traditionally been built in traditional materials such as brick and concrete. The construction material and construction techniques have not changed much in centuries, despite the high level of construction know-how that exists in UK. Most of the modern construction techniques are use for high-profile prestige buildings and commercial buildings. The housing sector does not seem to have benefited from the modern methods available.
This report aims at fanning-out the various modern methods of construction that can benefit the housing sector in many ways. Most of these modern methods are already used quite successfully in areas other than housing. The target will be to prove how, by means of modern construction techniques, affordable and sustainable housing can be developed.
Sustainability generally means sustained ability. It means being able for longer. It means being able to benefit from resources for longer, without endangering the depletion of the resources. Sustainable construction is an approach to construction that makes optimal use of resources throughout the lifespan of a building. This includes the resources utilised for the construction of the building, its operation and maintenance, and its eventual disposal. Resources here relate to sources of material, energy, space and money. Those are the basic requirements for a building.
It also makes economic sense to use as less resources as possible. So, achieving sustainability should not cost extra to the client, although it may cost extra initially to build the building. A typical building uses many times more resources during its lifespan than during its construction. So globally, it will be in the client's interest to go for sustainable methods.
Sustainable construction (Stern and Knapp, 1993) could also be distinct as those buildings that have minimum adverse impacts on the built and natural environment, in terms of the buildings themselves, their immediate surroundings and the broader regional and global setting. The rational use of natural resources and appropriate management of the building stock will contribute to saving scarce resources, reducing energy consumption (energy conservation), and improving environmental quality.
A general strategy for environmental conscious design (Boontra, 1997) consists of three main steps:
- Reduce the material demand - Any client, investor or governmental body should thoroughly evaluate the need for a new building activity by investigating the possibilities of reuse and renovating existing buildings. Designers should design a building as efficiently as possible by minimising the amount of resources needed. This can be done by optimising both the floor plan and construction.
- Application of renewable and recycled sources - By application of renewable and recycled sources the life cycle of building materials can be closed. Designers should also allow for future recycling. Designing a building for dismantling and not for demolition is one approach.
- Select materials with the lowest environmental impact - The environmental impact of materials is caused during a building's complete lifetime. Typical environmental issues are raw materials, embodied energy, emissions, hindrance, waste, recycling, repair, lifetime.
Throughout the report, it will be demonstrated that the modern methods proposed will respond positively to the above environmental criteria.
Buildings account for the largest proportion of energy consumption in most western societies. In UK for example, (Nicholls, 2002) energy consumption in buildings account for 45% of the total UK energy consumption. Energy is widely produced by burning fossil fuel such as petrol and coal. It is also used by nuclear fission of Uranium. Both processes are very harmful to the environment.
Why are Modern Methods Important for a Major Housing Developer?
Previously, sustainability was associated with environmental issues. However, in recent years it has been recognised that one cannot preserve environment at the expense of socio-economic progress. Sustainability is now being redefined in many circles as a balance of:
- Economic - stable economic growth and employment
- Environment - protection of environment and prudent use of natural resources
- Social - social progress for everyone
For these reasons, it is not only important that construction is clean and energy efficient, but it is also important to consider other factors such as the impact of the construction on its immediate neighbourhood and the society in general. The cost of construction has a direct impact on the cost of the housing. It is important to make housing economically viable and affordable without cutting down on our margin.
Legal Developments in Sustainability
There have been several recent legal developments in the area of sustainability that will have a definite future impact on our operations on the UK housing market. Most of these legal developments follow the 1997 Kyoto Earth Summit and are in line with the current government's emission and energy targets. The main developments are:
- UK Sustainable Construction Strategy 2000
- UK Energy White Paper 2003
- Sustainable Building Task Group 2003
Some of the impacts of these legal developments are already being felt. For instance, Part E and Part L of Building Regulations are already being revised and will be more demanding in terms of thermal and acoustic performance of buildings. There are several assessment methods being developed to measure quantify and rate the performance of a building in terms of how sustainable it is, and many of these measure will be taken into account for planning permission purposes. One of them is the BREEAM rating, developed by the Building Research Establishment. The BREEAM is an environmental assessment for offices, industrial and retail buildings. It consists of a checklist with scores for energy use, transport, water use, pollution, materials, land use etc. It has four ratings: pass, good, very good and excellent.
Another such assessment method is the Eco-Homes, which is applied to housing sector only and therefore more relevant to us. The Sustainable Building Task Group 2003 has put forward a recommendation for a Code of Sustainable Building, which is based on the BREEAM rating but is simpler. The Code has the full backing of the government and is currently compulsory for social housing sector. Although it is not compulsory for our market yet, it is more than likely that it will become so in a near future.
Another assessment method that may become important in the future is the WRAP, which measures the recycle content of a building. As for now, any building must have a minimum of 10% of recycle content. Most buildings will easily meet that requirement, even those built by the traditional methods. However, it is the intention of the authorities to steadily increase that 10% requirement in the coming years and it will become increasingly difficult to meet by traditional builds. WRAP is critical for planning permission and it is in the long term interest of the company that we start using methods that will introduce higher recycle contents in our housing developments.
Health and Safety
Health and Safety is becoming more and more important for the government and also for private clients. The upcoming CDM regulations 2006 will have major changes that put a lot more responsibility on the clients. Consequently, it can be expected that client will be putting health and safety high in their agenda and will chose their developers and contractors with that in mind.
Also the HSE is being more and more demanding about the standard of health and safety and work and checks are done on a regular basis on sites across UK. It is therefore important to be proactive and take a holistic approach towards health and safety. Instead of simply supplying more boots and helmets to site, it will be wiser to adopt methods that are inherently safer.
Typically, a housing development will either consist of some blocks of flats with parking space or a series of 2 to 3 storey houses, depending on the locality and the client. In both cases, the construction process is the same, although some differences in scale of operations may occur.
After the planning and survey stages, the first step in the construction process is the substructure. The substructure is that part of the building that is below the ground level. Its purpose is to safely transmit all forces to the ground. Traditionally, the substructure will consist of a series of pad foundations, strip footings, basements or even piles. Most of the old houses have basements whereas newer houses tend to have strip footings. Taller buildings such as apartments or where the building is on weaker grounds, piles may be required. All those foundations are generally formed by digging a hole in the ground and filling it with concrete. The shape, size and depth of the hole depend on the type of foundation being built. Foundations are labour-intensive and time-consuming work. All of the work has to be done on site, exposed to weather conditions. It also produces significant amount of noise and dust during the digging of the ground. Once the trenches or holes are filled with concrete, the site ends up with an excess of soil from the hole.
The superstructure is the visible part of the building, built on the foundation. The structure for houses will consist of building up brick walls from the ground, brick by brick. Each wall will consist of two leaves of brick with a gap in-between for insulation. The internal floors are generally made of heavy timber joists supporting secondary timber members and finally a plank topping, all nailed together and supported off the brick walls. The brick wall construction will continue until the roof level is reached. At the roof level, a timber roof is built in a way similar to the floor.
Recently, concrete columns and beams have been used along with the brick walls. Floors and roofs in newer construction tend to be on concrete, cast in-situ on formwork, supported off the concrete frame members. These methods are very time-consuming and labour intensive and almost all the work has to be done on site.
Partitions and Finishes
The internal partitions are either timber frames with ply-wood on each side, or single-leaf brick walls built in the same way as the external walls. Stairs are generally of wood.
The space heating, electricity, air-conditioning and ventilation are all built to suit the building in place.
Modern Approach to Construction
As opposed to the traditional method where each step of the construction is done independent of each other, the modern methods of construction differ right from the approach to the construction process. The thinking process behind the site works is done well in advance, to allow much better coordination between the various trades involved. The planning stage will think of the proposed and future uses of the building. The design stage is the most important stage of construction as decisions taken at the design stage have the highest impact of performance, economy and many other factors.
The approach to modern construction is one that takes sustainability and life-cycle cost of a building right from the onset of the design stage. Many factors can be influenced if thought is given at design stage. The following chapters will now introduce modern techniques used in construction that will result in more economic and sustainable construction in the housing sector.
Steel Framed Buildings
The use of steel is not new in construction. It has been used for over a century now. However, its full potential has only recently been understood. Steel has the potential to radically change the building and running cost of a building as well as having a major impact on issues such as sustainability, material demand, health and safety and so much more. Developments made over the past decade in steel construction have made it the most exciting material for construction.
Steel's Role in Sustainable Development
Steel is a completely different material from concrete and masonry. It is first of all homogeneous as opposed to a mix and is much stronger. The UK steel construction industry in a very efficient industry and steel can be used to our advantage as a modern construction material for several reasons that will be unveiled below (SCI, 2004).
More sustainable Design
Good design is fundamental to sustainable construction (SCI, 2004). Decisions made at the initial design stage have the greatest effect on the overall sustainability impact of projects. Steel's high strength-to-weight ratio is exploited in light structures which have low overall environmental impact and often require fewer and lighter foundations than alternative methods of construction. Its long-span capabilities create flexible spaces that facilitate changes in use during the life of the building, maximising letting potential and reducing refit costs.
The energy associated with the occupation of buildings (operations energy) dominates that used in their manufacture and construction (embodied energy) typically by a factor of between 4 and 10 over a 60 year design life. Reducing operational energy consumption reduces environment impact as well as saving money. Steel frames and associated composite or other type of floor slab achieve high levels of fabric energy storage, which can significantly reduce the energy bill for cooling. Steel-based cladding systems for industrial buildings and light steel-framed residential construction provide well-insulated and airtight solutions.
More sustainable manufacture and erection
Construction can have significant social and environmental impacts such as noise, dust, ground and surface water pollution and traffic congestions (SCI, 2004).
Steel provides the opportunity to maximise off-site construction techniques. Working in a factory under controlled conditions will definitely result in more accurate products and less waste. It also provides a safer and better working environment for the workers.
Computer-sided design and manufacture can be put to best use in steel construction to eliminate defects and reworks and to minimise waste. Any steel waste is generally recovered and recycled. Cost, and therefore time, remain key drivers in construction. Steel construction allows us to build fast and reliably, with minimal time spent on site. The small amount of time spent on site has many impacts such as lower noise, less time for the workers to work as height, less noise and dust, less traffic and the whole community benefits. Less time spent on site also has the advantage of fewer interruptions due to weather, which is a very important factor in the UK, because our weather is world famous!
As an example of what can be done (SCI, 2004), the 1600 tonnes of steelwork in the TNT Fastract distribution centre was erected in only 21 days!
Sustainability in Use
Designing a building for long life maximises the payback over the initial investment and is also a key aspect of sustainable construction. In that respect, refurbishment of a building to extend its life is very important. The versatility and flexibility of steel permits the owner of the building to easily modify and adapt to changing time without having to demolish and rebuild, thus extending the life of the building and getting the most value out of it.
Steel is a stable product and if protected from the environment with paint, will require little maintenance and will not deteriorate at all with time. Cladding systems associated with steel construction are also easily modified and allow easy access for maintenance.
With changing times, the requirements of a building change and therefore modifications may be necessary. Steel is easy to modify and to extend to suite new needs.
Sustainability at end-of-life
A concrete building only has a market value as a built-entity. The material itself can hardly be reused because it is cast-in. and cannot be dismantled. The best use of demolished concrete is land-fill. However, steel buildings have a material value even after construction. Because steel buildings consist of independently prepared members joined together by bolts, these members can be dismantled and re-used if the building is no longer required. For example, when the various Paris market halls built by Baltard in 1854 could no longer satisfy the needs of the city (ECCS, 2002), their function was transferred to Rungis, and the buildings replaced by the Centre Pompidou and the Forum. Recognising the need to preserve important architectural examples from the past one of the market halls was demounted and transferred to Nogent-sur-Marne, where it was simply reconstructed. It now accommodates cultural activities.
The fact that a steel building can be demolished and rebuilt using the same structural members has far-reaching advantages. The immediate advantage that comes to mind is the market value of the building. Of course, a building has a value when it is in use. But with the use of steel, the building will have a value even after its life-span. The steel members can be sold as separate entities or the whole building can be sold to be built on a different site. This contributes enormously to the cost of redevelopment and therefore can be used to reduce the cost of housing.
Looking at the bigger picture, re-using the same material for a new building implies that the natural resources that would have been required for the new building have been spared. Finally, even if the steel is not re-used directly as a construction material, it can always be recycled for new steel members. Steel is 100% recyclable material.
Energy in Buildings
In buildings, energy is required for:
- Space heating
- Domestic hot water heating
- Mechanical ventilation
- Air conditioning
- General electrical services such as lifts and escalators
The quantities of each of the above required vary from place to place and from building to building.
In UK as in the rest of Europe, space heating is traditionally achieved by gas-powered or electric powered hot water boilers that distribute the hot water to radiators. The envelope of the building is designed to retain as much of that heat as possible to save on energy. However, there are several innovative techniques now available that are very efficient.
New Glazing Technology
There are new types of glazing that allow the solar heat to go into the building, but not out. Double glazing systems have been used for many years, but now the double-glazing makes use of special glasses. The gap in-between the glasses can be filled with special gases that promote the greenhouse effect. In some cases, simply evacuating the air from the gap works marvellously in acting as a smart glazing system. There are glasses that can be switched from clear to opaque by the action of current, heat, or naturally like sunglasses. New cladding materials used on the walls are translucent. They transmit light and solar energy but act as insulants.
Interactive windows and shading system are computer-controlled to change the level of shading and ventilation at different times of the day to optimise energy use.
Direct sunlight is used to warm buildings. But solar energy can be used indirectly as well. Solar water heaters are very popular in the Southern Hemisphere. In Europe and especially in Western Europe, people have the misconception that because of the cold climate, solar water heaters will not be effective. In fact, solar water heaters are very efficient even in cold regions. It is also very cheap to build or buy one. It can be used on large scale for schools and hospitals with large roof plans. So instead of boiling water in a gas or electric boiler, solar water heaters can be used. Even if in winter the solar water heater cannot produce sufficiently hot water, it can still be used to preheat the water supplied to the boilers.
In many countries, space heating is required at night more than during the day. In such cases, the mass of the building can be made to heat up during the day by the solar energy methods described above. This mass will absorb this energy during the day but will only start dissipating it after several hours. Concrete floors for example will have a typical time lag of nine hours. Proper use of this thermal mass can lead to very significant saving in energy. The orientation of the building can play a crucial part as well. For example, if the south face is the one that is most exposed to direct sunlight, having more massive walls on the south will improve on the use of thermal mass.
Domestic Water Heating
Domestic hot water is used in almost all buildings. Solar water heaters as described previously are generally very effective for domestic hot water. Other methods can also been used, depending on the location. If a village is situated not very far from a volcano, they can usually dig deep boreholes and pump the water to the bottom of the hole where the earth temperature is quite high. They can pump back the water and use it as domestic hot water. The concept is not a new one. Thermal spa and natural hot water baths have been used for centuries.
The orientation of a building can be very important to make use of as much natural light as possible. Smart glazing systems discussed before are also very useful and are used more and more now. Lightwells and atria are also more and more used both for its help in natural lighting and ventilation, but also for its aesthetic contributions. When artificial lighting is required, special low-energy bulbs can be used that give the same amount of light but consume smaller amount of energy.
Natural ventilation has always been used in houses by simply opening and closing windows as required. Commercial buildings have however opted for more high-tech methods such as fans. These can be replaced by careful planning of the openings, of the way the floors are compartmented, and by the use of features such as atria. Also, computer-controlled openings are the high-tech version of manually opening and closing windows as required.
Cooling is always more expensive than heating. Not only does air conditioning consume a lot of energy; it also releases CFC's, which are harmful to the ozone layer. The use of these can be minimised as well. The use of ventilation can be used to improve the comfort level of occupants. The use of the thermal mass concept can also be used in the same way. The floors are cooled at night using natural ventilation, and during the day, they are used to cool the air inside the building.
The aim of the report was to propose and justify modern methods of construction. The report has exposed the necessity to shift to modern methods of construction. It is not just an option worth considering. It will soon be the only option and unless we as a company start the shift now, we will loose a competitive advantage.
Among the modern methods mentioned, steel construction comes out to be the flagship of modern, economic and sustainable construction methods. Added to that, other means such as using thermal mass, natural ventilation and natural heating and cooling can be used in combination to wonderful effect.
However, the most important point to remember is not the material or any particular technique. It is the approach and the thinking process required to meet the economic needs of the company, satisfy requirements from the government and other authorities and yet be able to produce affordable and high quality and high performance housing for the future.
Egan, Sir John, Rethinking Construction, Department of Trade and Industry, 1998
David Stern and Daniel Knapp, Reuse, Recycling, Refuse and the Local Economy: A Case Study of the Berkeley Serial MRF (documented by Urban Ore, Inc., and The Centre for Neighbourhood Technology: October, 1993).
Boontra Chiel, Sun at Work in Europe, Vol. 12, No.1, March 1997, p3.
Nicholls, Richard, Low Energy Design, Interface Publishing, 2002
European Commission for Constructional Steelwork, Merits of Steel, 2002 http://www.szs.ch/merits/vorwort_e.html
Achieving Sustainable Construction: Guidance for clients and their professional Advisers, Steel Construction Institute, 2004