Introduction
Taking down old buildings and replacing them with new is a process that has been going on for thousands of years. The destruction of buildings might have occurred during battles or attacks on towns; or due to natural disturbances such as earthquakes or volcanic activity. The resultant ruins would need to be removed and rebuilt. So the idea of demolition would have come about where a population wished to re-inhabit a specific area or site. (One famous example is the Holy Temple in Jerusalem which was deliberately destroyed by the Assyrians around 586 BCE. After 50 years of occupation the Jews returned to Jerusalem and began the re-construction of the second temple which took seventy years to complete.)
However the actual word to demolish only came into being in 1570, and was used from then on to mean the deliberate taking down or destroying of a building or structure.
Preserving the past – preparing the future.
In a country like Britain with very dense populations per square mile, there is a limited amount of land available for development. The land between built up areas of the villages and towns is known as Green Belt and is protected from development to preserve the agricultural and natural heritage which is vital to the economy of the country.
The outcome of this policy is that there is a constant shortage of land for housing and industry, so the developers have to be more creative when providing structures for the population. One of the ways of doing this is to find places where the buildings are no longer commercially viable or have been abandoned, and re-use the area for different purposes. These areas are known as brownfield, or greyfield sites. In some cities, particularly Leeds and Manchester, the old warehouses or factories have been converted into apartments, retaining the original shell and reconfiguring the internal dimensions into desirable living accommodation.
Brownfield sites are disused industrial and commercial facilities where the land may be contaminated with hazardous waste or pollution. They are potentially valuable for significant redevelopment once they have been cleaned up. Greyfield sites are urban properties that have been underutilised or abandoned, but do not have the environmental issues of brownfield sites. They were termed greyfield sites because of large areas of asphalt that covered the land. These sites are valuable because they already have the infrastructure such as water, sewage, electricity and gas in place and do not need remedial work to develop the site.
When a structure is to be removed there are different ways of approaching the task. The size and construction of the building, the new use of the site and whether there are valuable elements suitable for re-use, will all determine how it is to be demolished.
Traditional Demolition
Traditionally, once all the services were disconnected, the machinery and men would go in and just knock down the walls which caused the roof to collapse and then drag all the remains away. Any concrete hard standing would be broken up ready for removal. The previous excavation system would just clear waste to landfill sites. However modern demolition practices are very controlled and are subject to strict planning, safety and monitoring regulations.
Small structures such as two or three storey houses can be dismantled quite easily with hydraulic excavators and bulldozers using an undermining process. The walls are undermined at the base, in order to topple the structure; at the same time the manner and direction of the fall is controlled. Clean-up and safety issues are also taken into account when deciding how the building will be undermined and demolished.
Larger buildings such as tower blocks and chimneys require more specialist techniques, and are outlined below.
Deconstruction
A new approach to demolishing buildings is deconstruction – a green approach. The aim is to minimise the amount of waste going to landfill sites by carefully preserving valuable materials for reuse. The work may be a painstaking task of dismantling by hand – brick by brick – or beam by beam. The reclaimed materials are then recycled or re-used for future buildings. The results of deconstruction can save in excess of 90% waste from going to a landfill site. When the farmer opposite to my house sold his farm yard with barns for housing, the builder demolished the barns, cleaned up the bricks and reused them for the perimeter wall of the farmhouse. At the time I was looking for some rubble as a base for a path and the builder let me take several barrow loads off his pile.
Recycling
Historically when old buildings were ruined from disuse or war damage the local people would gradually remove the stone and use it to build their new structures such as houses or barns. Hadrian’s wall between Carlisle and Newcastle has mostly vanished because after the Romans left, the local population made off with the beautifully dressed stone the Roman craftsmen had used in the building of the wall. So even in those days people understood the value of recycling because it was much cheaper than having to quarry and dress the stone themselves.
At one time the rubble resulting from a demolished building would be taken to a landfill site for disposal. Now however concrete can be rapidly broken up with the latest machine called a guillotine and the resultant rubble can be crushed and used as sub-base material for the foundation of the new building which is to replace the old, or sent to other construction sites. These days this crushed rubble is called 6f2 crushed stone or 6f2 crushed material.
Modern machinery and techniques allows the demolition companies to efficiently segregate waste types on or off-site. Wherever possible construction materials are recycled and re-used in the new structure. Recycling of waste contributes to a considerable savings in project costs and is good for the environment.
When we renovated our bungalow 20 years ago the builder, who was a bell ringer, found an old beam from a bell tower that was being renovated, and after carefully treating it, installed it in the kitchen. It gave the room some badly needed character and has never needed any further treatment.
Copper pipes, wiring, roof tiles or slates, floor tiles and doors, and wood panelling are some of the valuable artifacts that are saved for recycling and re-use. There are specialist yards in many towns where reclaimed old or antique artefacts are available for purchase.
Tall Buildings
When planning a demolition of very large buildings skilled techniques are required. In some cases a wrecking ball on a crane may be used to demolish the top part of a tall building until it is down to a manageable height. However this process is rarely used by professional demolition companies today due to the uncontrollable factor of the swinging ball and the proximity of other buildings.
Other methods of demolition of tall buildings are by implosion using explosives, controlled collapse and piecemeal. Also ‘High Reach’ demolition excavators are used where explosives are not possible. Once the building is down to a more manageable height demolition continues in the usual way.
The steeplejack Fred Dibnah became famous in the late 1970′s for his work on demolishing tall chimneys without the need for explosives. He would cut an ingress at the base of the chimney, use wooden props to support the brickwork and then burn the props so that the chimney toppled hopefully in the right direction.
The tallest building to be lawfully demolished was the Singer Building of New York in 1967/8. More recently the collapse of the World Trade Centre after the 9/11 attack in 2001 illustrates the terrible devastation that could occur if the demolition is not controlled and very carefully contained.
In the demolishing of tall buildings and large structures water hoses and spray equipment is used to control the dust and would is termed a wet demolition.
Explosions
What comes to mind for many people when they think about demolition would be the dramatic collapse of a tall building using explosives. However it is usually the process of implosion, using explosives, that brings down a tall building so that it does as little damage as possible to the surrounding environment. Implosion is essential for dense urban areas and is very fast, the collapse taking only seconds, with the building crashing inwards into its own footprint.
Using explosives is specialist work and is a very skilled process and getting it wrong can be catastrophic. If an implosion is not prepared correctly the danger may be damage to neighbouring structures or even killing onlookers from flying debris. Even more dangerous is a partial collapse of a building where the remaining structure is unstable and there are still primed explosives that failed to go off. Workers are in great danger if or when continuing the demolition.
Other hazards of working with explosives occurs when the atmospheric pressure from low cloud above the implosion site will cause the shockwave to spread outwards instead of upwards. The wave of energy and sound created will break windows and cause other damage to the surrounding buildings.
Because of the dangers of working with explosives, implosion will only be used when other methods are too costly or impractical.
Health and Safety
Demolition of any building is highly dangerous and is a much more complicated and technical process than most people would realise. Experienced and skilled operators are essential to ensure safety for both workers and public alike. The stability of any structure is reliant on the interdependence of its component parts, so an incorrect sequence of dismantling could result in an accidental collapse.
Health and safety is paramount in demolition work so personnel working in the industry have to be thoroughly trained. It is advisable for operatives to have gained a Certificate of Competence in Demolition to ensure they have the necessary skills and safety awareness. All demolition work is regulated by the Construction, Design and Management Regulations.
Sequence of Demolition
There has to be a sequence of actions before any demolition can take place. Each area council will have their own specific list for planning approval, but a typical order would be as follows:-
- Provision of Information
The demolition company must provide information about the construction to be demolished, its previous use and the appropriate demolition method to be applied including disposal of hazardous substances.
- Survey of Demolition
Identification of any structural problems as well as risks associated with hazardous or flammable substances these include asbestos and require asbestos surveys be performed.Where petrol has been stored, in a disused garage for example, precautions need to be taken to prevent a fire hazard.
- Preferred and Safe Method of Work
A reputable company involved in demolition will be able to select the appropriate method of disposal. Planning and outlining the dismantling process is necessary for assiduous monitoring. A detailed statement outlining the safety process needs to be agreed by all parties involved before any demolition can take place.
- Preparation and Planning
There is a lot of preparation to be done before starting work on demolishing the building itself. Issues such as asbestos abatement, disconnecting utilities, rodent baiting, dealing with hazardous substances and making safe any electric, gas or other services have to be resolved.
- Protection of the Public
Where demolition is carried out in heavily populated areas the protection of the public is paramount. Safety cannot be compromised. Temporary services may need to be arranged, health hazards assessed and people disturbed will need to be informed.
Conclusion
The word ‘demolish’ is interpreted as the deliberate and controlled collapse of a structure. Demolition work is a very risky business and demolishing any building is a complex and skilled process. The aim in demolition is to remove an unwanted building as safely and quickly as possible, recycle or re-use most of the old material, and clear the site ready for the subsequent use.
In the centre of Nottingham over the last few years there has been a major reconstruction of what was an old car park into a brand new shopping centre. While this was going on the public were only really aware of the boarding around the area, a change in traffic direction and maybe some big lorries going in and out of the site.
So the next time you see buildings being demolished to make way for the new, give a thought to the company involved who’s team are daily working in a dangerous environment, adhering to all of the regulations and carefully and meticulously carrying out the project to bring us the modern conveniences we have come to expect and clearing the way for the future.