CDM Regulations for Domestic Clients: What Homeowners Need to Know

Introduction

The Construction (Design and Management) Regulations 2015 — universally known as CDM 2015 — are the principal piece of health and safety legislation governing construction projects in the UK. They apply to home renovation and extension projects as well as to commercial construction. Many homeowners are unaware that CDM places specific legal duties on them as clients — and that failing to meet those duties, in some project configurations, could expose them to legal liability. This guide explains what CDM means for domestic homeowners undertaking extensions, loft conversions or renovation projects in NW3 and north London, in plain language. For related guidance on managing the construction stage, see our construction stage coordination guide and structural engineer's role guide.

What Are the CDM Regulations?

CDM 2015 is designed to ensure that health and safety is considered throughout the design, construction and use of buildings. The regulations set out duties for clients, designers and contractors. The key principle is that health and safety risks should be identified and designed out during the planning and design stages — rather than being managed (at greater cost and risk) during construction.

For domestic homeowners, the regulations divide projects into two categories based on whether more than one contractor will be working on the project at the same time or in sequence.

Single-Contractor Projects

If your project involves only one contractor — a single building firm that employs or subcontracts all trades — CDM duties are relatively straightforward for the domestic client. In this configuration:

• The contractor takes on most of the CDM duties that would otherwise rest with the client
• The domestic client is not required to appoint a Principal Designer or Principal Contractor
• The contractor must comply with CDM duties including providing pre-construction information about site hazards, managing health and safety on site, and keeping a construction phase plan
• The designer (your architect) must consider health and safety in their design — designing out foreseeable risks where practicable

Most straightforward domestic extensions and loft conversions involving a single main contractor fall into this category. Your obligations as a domestic client are limited — you must provide the contractor with any information you have about the site that is relevant to health and safety (e.g., asbestos surveys, underground service locations, structural survey findings).

Notifiable Projects: More Than One Contractor

A project becomes notifiable under CDM 2015 when it will last more than 30 working days with more than 20 workers working simultaneously, or when it will exceed 500 person-days of construction work. For most domestic extensions in NW3, this threshold is not reached. However, if your project involves more than one contractor — for example, a main contractor and a separately appointed specialist (such as a basement waterproofing contractor, a steelwork contractor or a glazing specialist appointed directly by you) — the project may require the appointment of a Principal Designer and Principal Contractor.

Principal Designer

The Principal Designer (PD) coordinates health and safety during the pre-construction phase. They ensure that health and safety information is gathered, that designers work together to eliminate or reduce risks, and that a pre-construction information pack is prepared before the construction phase begins. On domestic projects, the architect typically takes on the Principal Designer role where it is required — this should be explicitly agreed in the architect's appointment.

Principal Contractor

The Principal Contractor (PC) coordinates health and safety during the construction phase. They are responsible for preparing and maintaining the construction phase plan, managing site safety, and ensuring that sub-contractors are briefed and coordinated. The main contractor typically takes on this role.

Practical Implications for NW3 Homeowners

Asbestos

Pre-1999 buildings — which includes virtually all Victorian and Edwardian properties in NW3 — may contain asbestos-containing materials (ACMs). Before any refurbishment or demolition works begin, you must commission an asbestos survey from a licensed surveyor. ACMs must be removed by a licensed asbestos removal contractor before general building works proceed in the affected areas. The CDM regulations require this pre-construction information to be shared with the contractor and (where appointed) the Principal Contractor.

Services Information

Before excavation for extensions or basements begins, you must provide the contractor with all available information about underground services — gas pipes, electricity cables, water and drainage runs — beneath the site. Your architect should commission a utilities search as part of the pre-construction information. Striking an underground service during excavation can cause serious injury and significant additional cost.

Construction Phase Plan

Even on projects that are not formally notifiable, your contractor should prepare a construction phase plan — a brief document setting out how health and safety will be managed on site. This includes arrangements for site access and security, storage of materials, management of hazardous materials, and emergency procedures. Requesting this from your contractor before work starts is good practice regardless of project size.

What CDM Means for Your Architect

Your architect has specific CDM duties as a designer. They must:

• Design out foreseeable health and safety risks where reasonably practicable — for example, designing roof structures that allow safe access for maintenance, or specifying window details that can be cleaned safely from inside
• Provide information about residual risks in the design that cannot be eliminated — so that the contractor can plan to manage them during construction
• Where appointed as Principal Designer, coordinate health and safety across all designers involved in the project

CDM compliance should be part of your architect's standard service. If it is not mentioned in their appointment letter, ask them to confirm how they will address CDM duties on your project. See our project risk register guide for broader risk management during the construction stage.

Conclusion

CDM 2015 is not just commercial construction law — it applies to domestic home renovation and extension projects and places real duties on homeowners, architects and contractors. For most straightforward single-contractor projects in NW3, the practical requirements are modest: provide the contractor with site information, commission an asbestos survey if required, and ensure your contractor has a construction phase plan. Where the project involves multiple contractors, the Principal Designer and Principal Contractor roles need to be formally established. Your architect should manage this on your behalf as part of their appointment. Use our free matching service to find an architect who understands CDM and takes project health and safety seriously as part of their service.