This guidance is for commercial clients, designers and contractors planning and managing alteration, demolition or dismantling work where the stability of the structure may be affected.
There is separate guidance on demolition for clients, designers, contractors, and building control on planning and managing health and safety for demolition work.
The law
The law (The Construction (Design and Management) Regulations 2015 on legislation.gov.uk) says that alteration, demolition and dismantling work must be planned and carried out by competent people to avoid unplanned structural collapse.
Commercial clients must provide contractors with relevant information about a building's structure, including stability and structural form and any significant design assumptions, suggested work methods and sequences. The contractor must then use that information to plan and carry out the work safely.
Workers and passers-by must be protected during the work, particularly from the collapse of a structure, and debris.
You’ll need to think about:
- survey and assessment
- preventing structural collapse
- arrangements for demolition
- consulting building control departments
There is more detailed guidance on the Construction (Design and Management) Regulations 2015 (CDM 2015).
Survey and assessment
A competent person should do a full survey and assessment of the structure before any potentially load-bearing parts of a structure are altered.
The survey and assessment of a structure should consider:
- the age of the structure
- previous use
- type of construction
- any nearby buildings or structures
Use this information to decide what steps are needed to prevent a collapse.
As the client you must also give your contractor a refurbishment or demolition survey that has been carried out by a competent surveyor.
Preventing structural collapse
A competent person should decide the method and design of temporary supports. Temporary support provided must be designed, installed and maintained to withstand foreseeable loads. Structures should never be overloaded.
Temporary supports
Temporary bracing and propping might be required if the structure, or areas of the structure:
- is known or suspected to be weak
- is subjected to increased loads during demolition, for example from machinery operating on floors or the build-up of debris
- has been erected with temporary bracing that did not form part of the finished structure and removing parts of the permanent structure could return it to an unstable state
- has cantilevers or hanging floors, and load paths could changed during the work
- has its footprint reduced during the work, so it becomes less stable laterally for a given height
- have parts, that are critical for stability, that could be damaged by falling debris
A suitably qualified and experienced engineer should decide if temporary support is necessary.
All bracing and propping should be designed by experienced temporary works designers. It must be installed, checked, inspected, maintained, and dismantled in accordance with the designer’s specification.
Demolition or dismantling arrangements should be written down before the work begins. This safe system of work may be in the form of a safety method statement identifying the sequence required to prevent accidental collapse of the structure.
A safe system of work may include:
- establishing exclusion zones and safe areas of work, clearly marked and with barriers or hoardings
- covered walkways
- using high-reach machines
- reinforcing machine cabs so that drivers are not injured
- training and supervising workers
More help on planning and managing demolition, including choosing demolition methods, is available in the guidance on demolition.
Scaffolding
‘Standard’ scaffold will not restrain a building during demolition or alteration.
Most ‘standard’ scaffolds in Great Britain are tied independent scaffolds. This means that, though they are independent for vertical support, they must be tied to a building for sideways support.
A scaffold will not allow a reduction in the size of an exclusion zone, it may increase it. This is because the presence of scaffolding means that, in the event of a collapse, the area where debris could fall is increased.
Use a scaffold designer or temporary works engineer
Scaffold around a building under demolition is not designed to take the sudden sideways loading that a partial collapse can exert and, as such, when used in conjunction with a high-reach machine, it should be fully designed by a scaffold designer or temporary works engineer and the full duties of the scaffold determined prior to any demolition taking place.
Sheeting
Standard scaffolds erected for access around a structure can allow sheeting to be attached to limit the escape of dust and retain small debris. Sheeting increases the effect of wind on the scaffold and with it the load applied to the building. Any sheeted scaffold reliant on tying to the structure for lateral stability must be reduced in height in accordance with a demolish and strike methodology, where the projection above the highest ties is controlled as the building is brought down. It must not act as a large sail above the partially demolished structure.
It’s possible to design scaffolds to restrain buildings, but this is a highly specialised area relying on the employment of a competent scaffold or temporary works designer. Scaffolding design must take into consideration the demolition method, sequence of works and changing load paths.
Where there is a need to restrain the building, facade retention (whether from fabricated steel or scaffold construction) must be designed by a competent person and, erected, inspected, maintained, and modified in line with their instructions and will likely require independent third-party checks of the temporary works.
Consulting building control departments
You should consult the building control department of the local authority in the area where a building is located before any structural alterations are made to a building.
The local authority is the enforcing body for building regulations.