Demolition
This guidance is for commercial clients planning demolition work, and also provides help on the role and responsibilities of designers, contractors and building control.
There’s separate guidance on structural stability during alteration, demolition and dismantling.
Demolition involves many people who all have responsibilities. Clients must appoint contractors and designers with relevant skills, knowledge and experience. The commercial client, with the help of the principal designer, must also provide pre-construction information to those who need it.
Principal designers must plan and manage health and safety in the pre-construction phase (before demolition starts). Principal contractors must plan and manage health and safety during demolition.
Site managers must ensure workers are supervised and are following safe working practice. Sub-contractors and site workers must follow the instructions and plans given to them, and ensure that their colleagues do too.
In law demolition work is treated the same as any other construction work. This means that the Construction (Design and Management) Regulations 2015 (CDM 2015) apply.
Before awarding the contract
The client should get advice from a competent demolition engineer before awarding a contract for demolition work. This is particularly useful for more complex jobs, especially when the site is in an urban area or close to a road.
Role of building control
You must give notice to the local authority, usually the local council’s building control department, at least 6 weeks before you intend to start demolition.
It’s better to contact the local authorities before you award the contract. This allows you time to discuss matters such as working time restrictions, traffic movements, scaffold licences and potential road closures.
Before granting permission, the local authority should consider the suitability of the demolition method being proposed for the structure and its location. If the work is complex, the site is in an urban area or close to a road for example, the local authority could ask a competent engineer to help them to assess any potential risks.
The council may specify pre-demolition requirements to reduce risk, sometimes known as a section 81 notice. They may also issue scaffold and pavement licences that include certain conditions.
Road closures
If the likelihood and consequences of a collapse is severe, and could result in material falling outside the site, a road closure might reduce risks. As the client, you should discuss any potential road closure with the local highway authority, usually the local council, before you put the work out to tender.
Asbestos survey and other information about the structure
As the client you must give your contractor a refurbishment or demolition survey that has been carried out by a competent surveyor.
Pre-construction information
Before they start work you must provide your contractor, and anyone else who needs it, with information you have about the structure. This is known as pre-construction information.
With the help of your principal designer, you should provide information about:
- the presence of asbestos
- structural stability of the site and nearby structures with their locations
- any alterations to the structure
- below ground live services in the work area
These should be done before work begins and not be left for the principal contractor to organise once the demolition work has started. If there is little information available about the structure, then you should consider getting a sufficiently detailed survey to confirm its form of construction. You can provide the results of this survey to all your contractors.
Method of demolition
Clients should get advice from a competent demolition engineer before awarding a contract for demolition work. A competent engineer should review the scheme for the contractor before work starts.
The demolition method must:
- be written by competent person
- take into account all hazards and risks associated with the structure and site
- correctly control the hazards and risks
If the job is particularly complex or the site is in an urban area or close to a road, for example, you should consider using a third-party to ensure that the method is appropriate.
Stability and controlling debris
Top-down demolition (progressively reducing the height of a building, floor by floor, using small plant), allows control of the stability of the structure and the build-up and spread of debris. This is often the preferred method for a town centre site, however, there may be circumstances where, following proper consideration, alternative methods, such as the use of high reach machines can be justified.
When selecting a method, make sure that any risks eliminated are not simply transferred elsewhere and end up putting others at risk.
During demolition, plan the work to ensure that in the event of a collapse, debris remains within a defined area, so a collapse cannot breach the site boundary.
There’s more detailed guidance on structural stability during alteration, demolition and dismantling.
Exclusion zones and safe working spaces
Your demolition method should include information about the site and where the planned safe working zones, exclusion zones and debris zones are.
The size of exclusion and debris zones depend on the demolition technique being used, the space surrounding the structure, and the distance over which debris can fall.
You may need to change exclusion zones throughout the course of a project depending on what work is being done. So, your plan should allow for this.
In the event of a deliberate or accidental collapse, debris must remain within that zone. Where space is not available for this, you should consider a more appropriate demolition technique.
A scaffold will not allow a reduction in the size of an exclusion zone around a building. Scaffolding must not be used to support structures unless it specifically designed as a support. There is more guidance on temporary support, and scaffolding’s role, in structural stability during alteration, demolition and dismantling.
A top-down demolition method, (progressively reducing the height of a building, floor by floor, using small plant working on the floors), allows greater control of both the stability of the structure and the build-up and spread of debris. Exclusion zones can therefore be smaller than for demolition methodologies involving high-reach techniques.
If there is little space around the structure at the site, it is likely that top-down demolition is the safest method. If, based on a suitable and sufficient engineering analysis, the contractor can show that an alternative technique can control the risks of collapse, then they can choose another method. To support their decision, they should carry out an analysis listing the pros and cons of the alternative techniques.
Choosing a method and sequence of work
All structures are different. When choosing the appropriate method of demolition, you’ll need to consider the structural form of the building, its load paths, floor loadings, shear walls, lift shafts and staircases. Full knowledge of the structure is essential.
Your decisions about the sequence and method of demolition should be based on the information gathered at the start of the project.
You must consider:
- structural form of the building
- condition of the building, including the effects of any historic alterations
- presence of any stability-sensitive elements, such as arches and overhangs
- how stability is achieved and can be maintained as the building is dismantled
- effects of debris build-up on the partly demolished structure
- locations of any stiff restraining features
- proximity of other structures and services
- whether there is the potential for unknowns that could increase the likelihood of an uncontrolled collapse
- space available around the structure
A sequence of work should be adopted that eliminates the possibility of an uncontrolled collapse. For example, elements not critical to overall stability should be removed first, with work then proceeding towards stiff elements such as braced cores.
The method of demolition chosen must be fully documented in the plan of work and be communicated to the contract team. If the structural fabric changes through the building, the demolition method may also need to change.
Protect workers and the public
Duty holders must ensure the safety of workers. This includes for those working at height and others on or near the site. You should try to remove the need to work at height by using a high-reach machine with a protected cab, for example. You should limit the escape of dust and debris.
You have a duty to protect those who might be affected by your demolition work, for example, other businesses and members of the public near the site. If the site is confined, with little space between structures being demolished and the site boundary, you must address the risk of an uncontrolled collapse and how it can be controlled. There may be issues for party wall surveyors to consider when drawing up agreements.
You will need to consider other topics when planning and managing health and safety for demolition work: