CDM Regulations for Small Builders: When They Apply & Your Duties

Quick Answer: The Construction (Design and Management) Regulations 2015 (CDM 2015) apply to virtually all construction work in the UK — including domestic projects. For projects with more than one contractor or lasting more than 30 working days (with more than 20 workers simultaneously) or 500 person-days, a Principal Designer and Principal Contractor must be appointed and the project must be notified to the Health and Safety Executive (HSE). Domestic clients have most duties transferred to the contractor automatically.

Summary

CDM 2015 is the legal framework governing health and safety management on UK construction projects. Many small builders assume CDM only applies to major commercial projects — this is wrong. The regulations apply to virtually all construction work, including domestic extensions, loft conversions, kitchen refits, and bathroom installations. What changes with project size is the extent of formal duties and documentation required.

The key thing to understand for domestic work is the duty holder hierarchy: client, principal designer, principal contractor, designer, and contractor. On a domestic job with a single contractor, most of the client's duties transfer to the contractor. On a job with multiple trades, the principal contractor duties require formal coordination.

CDM compliance is not a tick-box exercise — it is about genuinely planning for health and safety, identifying risks, and managing them. A well-run job where hazards are identified and controlled before work starts is CDM compliance in practice. The paperwork is secondary to the substance.

Key Facts

Quick Reference Table

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Project Type CDM Applies? PD Required? PC Required? Notify HSE?
Single trade, small domestic job Yes No No No
Multi-trade domestic job (e.g. extension with electrician, plumber, builder) Yes Yes (if >1 contractor) Yes (if >1 contractor) Only if notifiable threshold
Extension, 2 tradespeople, 8 weeks Yes Yes Yes No (under 500 person-days)
Large extension, 6 months, multiple trades Yes Yes Yes Likely yes
Commercial refurbishment, any size Yes Yes (if >1 contractor) Yes (if >1 contractor) If notifiable
HMO conversion, 3 contractors, 10 weeks Yes Yes Yes Check calculation
Notifiability Threshold Value
Working days exceeding 30 days with 20+ workers simultaneously
Person-days threshold 500 person-days total
Whichever occurs first triggers notification

Person-day calculation example: 4 workers × 10 days = 40 person-days. 10 workers × 60 days = 600 person-days — this project would need HSE notification.

Detailed Guidance

Does CDM Apply to Domestic Jobs?

Yes. CDM 2015 applies to ALL construction work — domestic or commercial, large or small. However, the specific duties that apply depend on the project type:

Domestic client projects (single homeowner):

Key point: Even a kitchen refurbishment by a single tradesperson must have basic health and safety planning — identification of asbestos, manual handling risk assessment, COSHH for dust and chemicals, work at height assessment if applicable. This is CDM compliance for a small job.

Roles and Responsibilities

Client (domestic or commercial):

Principal Designer:

Principal Contractor:

Contractors (all trades on site):

Construction Phase Plan

A Construction Phase Plan (CPP) is required for ALL construction projects — including small domestic work. For a simple single-trade domestic job, the CPP can be brief:

For a multi-trade project or notifiable project, the CPP must be more detailed and should be prepared before work starts.

What a CPP should cover (minimum for domestic projects):

  1. Project description and timeline
  2. Asbestos management — has asbestos been surveyed? What materials might contain asbestos? (See asbestos)
  3. Existing services — gas, electricity, water routes identified and marked
  4. Working at height — how will roof, scaffold, and ladder access be managed?
  5. Manual handling — any heavy lifts requiring mechanical aids or additional manpower?
  6. COSHH — dust control plan, chemical storage, PPE requirements
  7. Site rules — welfare facilities, access control, emergency contacts

Pre-Construction Information

Before starting a domestic project, the contractor should gather:

For domestic clients, much of this information may not exist — the contractor should make reasonable efforts to gather what is available and document what cannot be obtained.

HSE Notification (F10)

Notifiable projects must be notified to HSE before the construction phase begins using the F10 online form. The notification includes:

Notification is a legal requirement under CDM 2015. The notice must be displayed on site.

Frequently Asked Questions

I'm a sole trader working on a domestic extension — do I need a CDM Construction Phase Plan?

Yes — CDM 2015 applies to all construction work. As a sole trader on a domestic job, you act as both contractor and principal contractor. Your CPP can be simple — a document covering hazards, how you will manage them, and emergency contact information. The key is demonstrating you have thought about health and safety before starting work. Many professional bodies provide simple CPP templates.

What is the difference between a Principal Designer and the architect?

The Principal Designer role is often filled by the architect on projects where the architect has design influence. However, the Principal Designer is a CDM 2015 duty holder with specific health and safety responsibilities — it is not an automatic part of an architect's appointment. The client must specifically appoint the Principal Designer in writing. On projects without an architect (e.g. a builder-led extension), the builder or a specialist CDM advisor may act as Principal Designer.

Do I need to notify HSE for a 6-week kitchen extension?

Calculate the person-days: say 2 workers × 30 working days = 60 person-days. That is well below the 500 person-day threshold. Unless more than 20 workers will be on site simultaneously for more than 30 days (extremely unlikely for a domestic kitchen extension), notification is not required. However, CDM duties still apply — Construction Phase Plan required.

What happens if I don't comply with CDM?

CDM 2015 is enforced by the HSE. Contraventions can result in improvement notices, prohibition notices (stopping work), or prosecution. The penalties for serious CDM breaches include unlimited fines and imprisonment. More commonly, CDM non-compliance is discovered in post-accident investigations — and can significantly affect insurance claims and civil liability if a worker is injured on a poorly-planned site.

Who pays for the Principal Designer on a domestic project?

The client pays — but on a domestic project, the duties transfer to the contractor. In practice, many contractors on smaller domestic projects either act as Principal Designer themselves (if they have appropriate competence) or appoint a CDM consultant for larger or more complex projects. The cost is modest for smaller projects and should be built into the project fee.

Regulations & Standards