Demolition

1 Introduction
2 Pre-demolition information
- 2.1 Planning permissions
3 Demolition procedures
4 Demolition methods
5 Materials disposal
6 Policy
7 Related articles on Designing Buildings
8 External references

[edit] Introduction

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 should adopt 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.

[edit] Pre-demolition information

The level and detail of pre-demolition information and surveys required should be proportionate to the project and might 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 materials 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 the historic use of buildings and land, contamination, mineshafts, wells and so on.
Constraints to demolition imposed by the client or by the site conditions.
Site finish required.
Pre-construction information (CDM regulation 10).

[edit] Planning permissions

Demolition requires notification to be submitted to the local authority to determine whether prior approval is required for the method of demolition where buildings are over 50 cubic metres, and for walls or gates.

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.

Where demolition works may have an environmental impact, a screening opinion may be obtained from the local authority to determine whether a full Environmental Impact Assessment (EIA) is necessary.

[edit] Demolition procedures

General demolition procedures include:

Site compound and security set-up.
Intrusive pre-demolition surveys (such as; asbestos survey for demolition, structural survey, hazardous materials surveys, etc).
Isolation of utilities and removal of meters.
Disconnection of utilities.
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.

[edit] Demolition methods

Demolition methods include:

[edit] Explosives

Explosives allow rapid and complete demolition where other methods may be dangerous or slow. 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). For more information, see Explosives.

However, recent developments in high-reach machinery mean that buildings less than 22 storeys are generally demolished by machine.

[edit] Hand demolition

These methods may be used for small-scale projects, or 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, adjacent structures, or structural instability.

It involves the progressive demolition of a structure by operatives using hand tools. In general, the order of demolition is the reverse that of construction.

[edit] Machine demolition

This is by far the most frequently-used method and reduces the need for people to work at height, or manual handling.

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 pushing arm. This is operationally limited by height, so a building should be reduced by other methods first.

[edit] Other methods

Other methods that can be used 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, this involves generating a thermal reaction which causes members to lose strength.
Thermic lancing: Drilling or cutting silica materials by thermo-chemical action.
Drilling and sawing: Used for cutting openings in reinforced concrete.

[edit] Materials disposal

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 furniture and equipment.

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 should be practical for a competent contractor to achieve 95% building recycling by mass, or even more for some structures.

Materials should be provided to WRAP protocols with Environment Agency certification. It is practical to crush on site for volumes in excess of 3,000 cubic metres.

For more information, see Site waste management plan.

[edit] Policy

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: