A construction phase plan is not something reserved for major developments or notifiable projects. HSE guidance is clear that every construction project needs one, including small domestic work. A recent prosecution involving a home extension is a useful reminder that even relatively modest projects need proportionate planning before construction starts. HSE

A domestic extension has put the duty back in focus

On 17 August 2026, HSE reported the prosecution of Adam’s Building Construction Ltd and its director following work on a domestic extension in Bradford. The extension had been constructed over existing gas service pipework and around a boiler flue without the necessary relocation work being carried out. HSE Media Centre

Building Control had reportedly warned the contractor several times about the gas pipework and flue. When the property was inspected in May 2024, the boiler flue was terminating inside the new extension and Northern Gas Networks classified the installation as immediately dangerous. The household gas supply had to be disconnected. HSE Media Centre

During its investigation, HSE found that the company could not demonstrate that it had prepared construction phase plans for its domestic projects. HSE subsequently served an Improvement Notice requiring a system for producing written plans where the business acted as principal contractor. The company later failed to comply with that notice. HSE Media Centre

The company ultimately pleaded guilty to offences under sections 3(1) and 33(1)(g) of the Health and Safety at Work etc. Act 1974 and was fined £10,000 plus £4,263 costs. The case should therefore not be simplified to “a £10,000 fine for not having a CPP”, but the absence of proper construction-phase planning was clearly part of HSE’s findings and enforcement action. HSE Media Centre

The rule applies to more than major projects

One of the most persistent misunderstandings around CDM is that formal planning only becomes necessary when a project is large enough to notify HSE.

That is incorrect.

HSE’s Construction Phase Plan guidance, CIS80, states that a construction phase plan is required for every construction project. HSE specifically gives examples including kitchens and bathrooms, structural alterations, roofing work, extensions and loft conversions. HSE

For projects involving more than one contractor, Regulation 12 of CDM 2015 requires the principal contractor to draw up, or arrange for the preparation of, the construction phase plan before the site is set up. Where there is only one contractor, Regulation 15 places the corresponding duty on that contractor. Legislation.gov.uk

The F10 notification threshold is separate. A project becomes notifiable where construction work is scheduled to last longer than 30 working days with more than 20 workers simultaneously, or exceeds 500 person-days. A project can fall well below that threshold and still require a construction phase plan. HSE

For a small builder replacing a roof, carrying out a loft conversion or building an extension, the plan may be short and straightforward. HSE specifically says the effort spent planning should be proportionate to the complexity and risks involved. HSE

Who carries the duty on domestic work?

Domestic projects sometimes cause confusion because the homeowner is technically the client but is unlikely to have construction health and safety expertise.

CDM deals with this by transferring most domestic-client duties to other members of the project team.

Where there is one contractor, the contractor normally takes on the domestic client’s duties in addition to their own contractor responsibilities. Where a project involves more than one contractor, those client duties normally pass to the principal contractor. HSE

There is an alternative arrangement where a domestic client has a written agreement with the principal designer for that principal designer to undertake the client duties. Without that written agreement, the duties normally remain with the contractor or principal contractor as described above. Legislation.gov.uk

This means a builder working predominantly for homeowners cannot assume that CDM documentation is somebody else’s responsibility simply because the customer is a private individual.

HSE’s guidance for small builders states that their duties begin as soon as they are appointed and that the planning for the work must be recorded in a construction phase plan. HSE

What should a proportionate plan contain?

The legislation does not prescribe a fixed page count or require a complicated management document.

Regulation 12 requires the plan to set out the health and safety arrangements and site rules for the construction phase and, where relevant, specific arrangements for particularly hazardous work covered by Schedule 3 of CDM. The principal contractor must also keep the plan under review and revise it as the project develops. Legislation.gov.uk

For smaller projects, HSE’s CIS80 template provides a useful starting point. It prompts builders to record matters such as:

• Project and key dates.
• Relevant information about the existing property.
• Services and isolation points.
• Asbestos information.
• Who else will be working on the job.
• How contractors will communicate and coordinate.
• The main site hazards and controls.
• Work at height and structural stability.
• Excavations.
• Dust and asbestos exposure.
• Site security and protection of the household or public.
• Welfare arrangements.
• Supervision and responsibility for running the job safely. HSE

The plan should reflect the actual project rather than simply reproduce every possible construction hazard.

For example, on a rear extension, existing electrical, gas, water and drainage routes may be far more important than generic information about tower cranes or large-scale site traffic. Where structural walls are being removed, temporary support and sequencing could become one of the central issues in the plan.

That is what proportionate planning should look like: less paperwork where the project is straightforward, but enough thought and detail to control the real risks. HSE makes the same proportionality point in its guidance to small builders. HSE

Why a generic template can still fail

Having a document titled “Construction Phase Plan” does not, by itself, demonstrate that the work has been properly planned.

The plan should capture how the construction phase will actually be managed. HSE’s CIS80 guidance asks builders to identify project-specific information, main dangers, communication arrangements, supervision and how changes will be managed. HSE

This becomes particularly important when conditions change.

Imagine an extension where the drawings initially assume a service will be diverted before excavation. Once work starts, the contractor discovers that the service remains live and conflicts with the proposed foundation.

The useful construction phase plan is not the document that continues to state “services to be identified before digging”. It is the management process that stops the work, confirms the service location, establishes who will arrange diversion or isolation and updates the construction sequence accordingly.

Regulation 12 expressly requires the principal contractor to review, update and revise the plan throughout the project so that it remains sufficient for the work being undertaken. Legislation.gov.uk

The recent Bradford case illustrates why this matters. HSE identified repeated warnings relating to the gas installation before the unsafe situation was eventually discovered by Building Control. A planning system should help ensure significant design or construction issues are identified, allocated and resolved rather than simply carried forward as the job progresses. HSE Media Centre

What should you do now?

If your business undertakes extensions, refurbishments, roofing, fit-outs, maintenance or other small construction projects, review how construction phase planning is currently handled.

Check whether every project has a plan before work starts, including domestic work. Confirm who is acting as contractor or principal contractor and whether domestic-client duties have transferred to your business.

Then look at the quality of the plan itself. It should identify the real project risks, arrangements for coordination and supervision, welfare, significant sequencing issues and how changes will be controlled.

A useful test is to ask whether somebody taking over the project tomorrow could read the plan and understand how the site is intended to be managed safely.

If the document is identical for every job except for the client name and address, it probably deserves another look.

Our professional view

The construction phase plan is often treated as another document needed before the site file is complete. That misses its value.

For a competent contractor or principal contractor, the CPP should be the written output of the thinking that takes place before construction begins: what are we building, what could go wrong, who is responsible, what information do we still need and how will we manage the work when circumstances change?

For small projects, that may genuinely fit onto a few pages. HSE itself provides a two-page template for straightforward work. The objective is not paperwork for its own sake; it is evidence that the job has actually been planned. HSE

Managers, contractors and designers who want a clearer understanding of these duties can use All Star Safety’s CDM 2015 Awareness eLearning course, which covers CDM dutyholders, construction phase plans and the application of CDM to domestic and commercial projects. All Star Safety Ltd

Businesses needing more direct assistance with construction phase planning, contractor arrangements or wider CDM compliance can also access All Star Safety’s health and safety consultancy service. All Star Safety Ltd