Demolition is the most high risk activity in the construction sector.
The essence of safe demolition lies in efficient risk control, environmental management and careful planning. The CDM Regulations have provided a platform from which the industry exhibits best practice, demanding written plans of work for demolition even where a project is not notifiable.
Clients and their professional advisors play a vital role in safe demolition and must:
- Allow sufficient time for planning the works.
- Procure an appropriate contractor (carry out safety and environmental audits).
- Provide sufficient information to a good standard.
 Pre-demolition information
The level and detail of pre-demolition information and surveys required are proportionate to the project and include:
- Asbestos demolition survey (to HSG264 standard).
- Utility information (showing disconnection locations if previously carried out).
- Structural hazards and risks (including relevant information such as condition, modifications, materials, etc).
- Hazardous material information and health hazards.
- Building regulations. Where demolition work is proposed, the owner must give the local authority building control department six weeks notice under Section 80 of the Building Act.
- Party Wall etc. Act notices.
- Desk studies indicating historic use of building and land, contamination, mineshafts and wells.
- Constraints to demolition imposed by the client or by the site conditions.
- Site finish required.
- Pre-construction information (CDM regulation 10).
Demolition requires prior notification to be submitted to the local authority for determination on whether prior approval is required of the method of demolition where buildings are over 50 cubic metres and for walls or gates.
Where demolition works may have an environmental impact, a screening opinion is required from the local authority on whether a full Environmental Impact Assessment (EIA) is necssary. Planning permission is required for demolition of unlisted buildings in conservation areas and listed building consent is required for demolition of any part of a listed building.
 Demolition procedures
General demolition procedures include:
- Effective building security and maintenance prior to demolition.
- Isolation of utilities and removal of meters.
- Intrusive pre-demolition surveys (such as; asbestos survey for demolition, structural survey, hazardous materials surveys, etc).
- Disconnection of utilities.
- Site compound set-up.
- Asbestos removal (in accordance with the Control of Asbestos Regulations).
- Soft strip (taking the structure back to construction materials including the removal of windows and door frames).
- Superstructure demolition with special measures as constraints demand, such as de-build or protection of adjacent structures.
- Processing of superstructure arisings.
- Slab and foundation demolition.
- Processing of arisings.
- Site finishes as required including provision for the future security of the site.
Some of the procedures by structural type include the following:
- Roof trusses: Temporary bracing provided to allow removal of individual trusses.
- Floor panels: Should be supported to allow cutting out, prior to lowering to ground level.
- Structural steel: Temporary bracing or steel ropes should be used to maintain a stable structure as members are lowered carefully to be ground.
- Structural concrete: Temporary supports should be placed under floors and beams while end anchorages are re-stressed and the tension slowly released before being cut and lifted out of position.
- Bridges: Work should be carried out in reverse order of erection, with as much dead load as possible removed without affecting stability.
 Demolition methods
Demolition methods include:
This requires extensive use of the police to enforce exclusion zones as well as pre- and post-demolition structural inspections for a substantial radius (in the order of quarter or half a mile).
Explosives allow rapid and complete demolition where other methods may be dangerous or slow.
Recent developments in high-reach machinery mean that buildings less than 22 storeys are generally demolished by machine.
For more information, see Explosives.
 Hand demolition
These methods are required when demolition has to be carried out in a more sensitive manner due to site constraints such as; proximity to uncapped mineshafts, overhead utilities, pedestrian access or adjacent structures, or structural instability.
It involves the progressive demolition of a structure by operatives using hand tools. Once they have been released, members are often used to lift them out, and as such, in general, the order of demolition is the reverse that of construction.
 Machine demolition
Common techniques include:
- Swinging ball: Heavy steel ball suspended from a crane jib.
- Wire rope: Can be used for demolishing parts of a structure.
- Pushing arm: A machine fitted with a hydraulic pusher arm. Operationally limited by height, so a building should be reduced by other methods first.
 Other methods
There are several other methods that can be used when conditions prohibit the use of explosives. These include:
- Gas expansion burster: Used for 'bursting out' concrete in a prepared cavity.
- Hydraulic expansion burster: Similar to gas but uses wedges and pistons.
- Thermal reaction: Used together with wire pulling. Involves generating a thermal reaction which causes the member to lose strength.
- Thermic lancing: Process of drilling or cutting silica materials by thermo-chemical action.
- Drilling and sawing: Used for cutting openings in reinforced concrete.
Buildings handed over for demolition generally contain hazardous waste, rubbish for landfill and recyclable material. Best practice use of site waste management plans for all demolition projects assists in ensuring the optimum recycling chains are in place. Clients can assist by handing over empty buildings and finding new uses for all furniture and equipment in a building before handing it to the contractor for demolition.
Demolition produces products suitable for construction with the general rule that a recycled material can be considered a grade lower than its original state. So crushed structural concrete for example may be used as blinding, though with full treatment and a designed mix, it may be possible to achieve structural grade concrete. At present, it is practical for a competent contractor to achieve 95% building recycling by mass, or even more for some structures.
NB, whilst it is not normally necessary to obtain planning permission to demolish a building (unless there are local restrictions such as an article 4 direction), permission is required for listed buildings and for buildings in conservation areas.
The Coalition Agreement outlined the government’s commitment to increase housing supply, tackle the problems that rundown vacant properties cause and help support local economic growth from refurbishment and improvements. In a written ministerial statement of 10 May 2013, Official Report, Column 13WS, ministers committed to revising outdated guidance issued by the former Office of the Deputy Prime Minister in relation to demolition.
On 16 January 2015, The Rt Hon Eric Pickles MP, Secretary of State for Communities and Local Government, confirmed that the following pieces of guidance no longer reflect government policy and so were cancelled:
- Neighbourhood Renewal Assessment and Renewal Areas (DETR, 1997).
- Private Sector Renewal Strategies: A Good Practice Guide (DETR, 1997).
- Running and Sustaining Renewal Areas (DETR, 2000).
- Addressing the Needs of Run Down Private Sector Housing (ODPM, 2002).
- What Works? Reviewing the Evidence Base for Neighbourhood Renewal (ODPM, 2002).
- Housing Renewal Guidance – ODPM Circular 05/2003.
- Sustainable Communities: Building for the Future (ODPM, 2003).
- Assessing the Impacts of Spatial Interventions: Regeneration, Renewal and Regional Development - The 3Rs Guidance (ODPM, 2004).
- Neighbourhood Renewal Assessment guidance manual (ODPM, 2004).
 Related articles on Designing Buildings Wiki
- Building regulations.
- Building survey.
- Conservation area.
- Construction dust.
- Crane regulations.
- Deleterious materials.
- Environmental Impact Assessment.
- Filtering facepieces.
- Health and Safety.
- Listed building.
- Notify HSE.
- Party wall.
- Planning permission.
- Pre-construction information.
- Pre-demolition audit.
- Pre-demolition and pre-refurbishment audits.
- Principal contractor.
- Recyclable construction materials.
- Risk assessment.
- Site waste management plan.
- Structure relocation.
- Structures at the end of their design life.
- Temporary works.
- Types of crane.
- Urban decay.
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