Do You Need a Construction Phase Plan? CDM 2015 Explained for Homeowners

If you are a homeowner commissioning building works — an extension, a loft conversion, a full refurbishment — you are already a legal duty-holder under UK health and safety law, whether you know it or not. The Construction (Design and Management) Regulations 2015, commonly known as CDM 2015, place specific duties on everyone involved in a construction project, including the client.

This post explains what CDM 2015 requires, when a Construction Phase Plan is needed, and why working with an experienced principal contractor matters when it comes to compliance.

What Is CDM 2015?

CDM 2015 is the primary piece of health and safety legislation governing construction projects in Great Britain. Its purpose is to ensure that health and safety is considered and managed throughout every stage of a project — from the earliest design decisions through to completion and handover.

The regulations apply to virtually all construction work, including domestic projects. They impose duties on three main parties:

The Client is the person or organisation commissioning the work. For domestic clients, CDM 2015 transfers many client duties to the principal contractor or principal designer by default — but this only works effectively if those roles are properly appointed.

The Principal Designer is responsible for managing health and safety during the pre-construction phase. They coordinate design work to ensure risks are identified and reduced at source, and prepare a Pre-Construction Information pack for the project.

The Principal Contractor is responsible for managing health and safety on site during the construction phase. This includes preparing and implementing the Construction Phase Plan, coordinating sub-contractors, and maintaining a safe working environment.

When Is a Construction Phase Plan Required?

A Construction Phase Plan is required on every notifiable project, and it must be prepared before the construction phase begins. Under CDM 2015, a project becomes notifiable — requiring the Health and Safety Executive (HSE) to be formally informed via an F10 notification — when it exceeds either of the following thresholds:

The construction phase will last longer than 30 working days and will have more than 20 workers working simultaneously at any point, or
The volume of work will exceed 500 person-days in total.

For most single domestic projects — a standard loft conversion or extension — these thresholds will not be met. However, even for non-notifiable projects, a Construction Phase Plan is still a legal requirement. The difference is that a non-notifiable project does not require the HSE to be informed, and the plan can be proportionate in length and detail to the scale and complexity of the works.

A plan for a straightforward domestic project may be relatively brief — but it must exist, it must be specific to the project, and it must be implemented.

What Must a Construction Phase Plan Contain?

CDM 2015 sets out the minimum content requirements for a Construction Phase Plan. It must cover:

A description of the project and details of the key duty holders
Arrangements for managing the significant risks identified during the pre-construction phase
Site rules and emergency procedures (including fire evacuation, first aid, and accident reporting)
Arrangements for managing sub-contractors and ensuring their competence
Welfare provisions for all workers on site
How the plan will be communicated to and followed by everyone working on the project

The plan is a live document — it should be updated as the project progresses and as new information about risk emerges.

Why the Principal Contractor Role Matters

For homeowners, the practical importance of CDM 2015 is this: if your principal contractor does not have a clear understanding of their CDM duties, the burden of compliance can fall back on you as the client. A contractor who does not prepare a Construction Phase Plan, does not brief sub-contractors on site rules, and does not maintain welfare facilities is not only creating legal risk for themselves — they are potentially exposing you to regulatory scrutiny as well.

Equally, a project where multiple trades are working without clear coordination increases the risk of accidents, poor sequencing, and quality failures — all of which CDM 2015 is specifically designed to prevent.

Working with a structured principal contractor who takes CDM compliance seriously is not a bureaucratic nicety. It is a genuine protection for workers, neighbours, and the client alike.

How RCB Handles CDM on Every Project

As principal contractor, RCB Design & Build manages all CDM 2015 duties so that our clients are properly protected. We prepare the Construction Phase Plan before works commence, coordinate all sub-contractors and trades, maintain compliant welfare arrangements on site, and ensure that the project proceeds in a controlled and safe manner throughout.

We also work alongside the appointed Principal Designer where one is in place, ensuring that pre-construction information is properly reviewed and incorporated into how the construction phase is managed.