What Is CDM 2015 and What Does It Mean for Your Building Project?
Introduction
The Construction (Design and Management) Regulations 2015 — commonly known as CDM 2015 — are the primary piece of legislation governing health and safety in construction. They apply to virtually every building project carried out in the UK, including residential projects — and they create legal obligations for everyone involved, including the homeowner who commissioned the work.
Many homeowners are unaware that CDM 2015 applies to their extension, loft conversion, or refurbishment — and are surprised to learn they have legal duties under it. This guide explains what CDM 2015 requires, who has duties, and what this means in practice for a typical London residential project.
What Is CDM 2015?
CDM 2015 replaced the previous CDM Regulations 2007 and applies to all construction work in England, Scotland, and Wales. Its purpose is to ensure that health and safety is properly managed throughout every stage of a construction project — from initial design through to completion.
The Regulations assign specific legal duties to different parties (called "dutyholders") depending on the size and nature of the project. The key dutyholders are:
- The client (the person or organisation commissioning the work)
- The principal designer (coordinates health and safety during the design phase)
- The principal contractor (manages health and safety during the construction phase)
- Designers (consider health and safety in their design decisions)
- Contractors (implement health and safety on site)
When Is a Principal Contractor Required?
A principal contractor must be appointed in writing for any project where there will be more than one contractor working at any stage. This covers almost all loft conversions, extensions, and refurbishments — where you might have a roofer, a structural engineer's groundworker, an electrician, and a plasterer all involved at different points.
If a principal contractor is not formally appointed, CDM 2015 places the principal contractor's duties on the contractor in control of the site. However, having a clear written appointment is good practice that protects everyone involved.
What Are the Client's Duties Under CDM 2015?
As a domestic client (a homeowner commissioning work on their own home), your legal duties are reduced compared to commercial clients — but they are not zero.
Your key duties include:
Appointing a principal designer and principal contractor in writing (where required). For most domestic projects, this is done as part of the contract with your contractor.
Allowing enough time and resource for the work to be carried out safely. This means not imposing an unreasonably short programme or withholding information that affects how safely the project can be run.
Ensuring that pre-construction information is provided to the principal designer and principal contractor before the design and construction phases begin. This includes information about the property — existing services, hazardous materials (asbestos), structural conditions — that may affect health and safety.
Keeping the health and safety file at the end of the project (for notifiable projects). This is a record of the project for the benefit of future owners and those working on the property.
What Is a Construction Phase Plan?
The principal contractor is required to produce and maintain a Construction Phase Plan (CPP) — a written document that sets out how health and safety will be managed during the build. It doesn't need to be a long document, but it must exist and be maintained throughout the project.
A well-run principal contractor will produce this as a matter of course. If your contractor can't tell you what a Construction Phase Plan is, that's a concern.
What Is Notification?
Projects above a certain scale must be notified to the Health and Safety Executive (HSE) before construction begins. Notification applies when a project is:
- Expected to last longer than 30 working days with more than 20 workers simultaneously, or
- Will exceed 500 person-days of construction work
Most standard residential extensions and loft conversions don't meet this threshold. But larger refurbishments or sequential multi-project programmes can.
Want a principal contractor who takes CDM 2015 seriously?
RCB Design & Build acts as principal contractor on all projects we manage, producing Construction Phase Plans and managing all CDM duties correctly from day one. Contact us to discuss your project.
📞 07359 872594 | contact@rcbgroup.co.uk | www.rcbgroup.co.uk