CDM 2015 — the rules every construction project must follow.
The Construction (Design and Management) Regulations 2015 set legal duties on every construction project in Great Britain — from new-build skyscrapers down to domestic kitchen extensions. As a homeowner you have client duties, but in most cases your contractor inherits them. Notifiable projects (longer than 30 days with 20+ workers, or over 500 person-days) need formal HSE F10 notification.
Does CDM 2015 apply to my house extension?
Yes — the Construction (Design and Management) Regulations 2015 apply to every construction project in the UK, including a homeowner's extension or loft conversion. As a domestic client your duties are limited (and pass to the contractor in most cases). Notifiable projects — longer than 30 working days with 20+ workers simultaneously, or over 500 person-days — require formal HSE F10 notification before work starts.
Project length triggering F10 notification (with 20+ workers).
Alternative trigger for F10 notification.
CDM-related HSE prosecution average — fatal incident significantly higher.
CDM 2015 — the terms that matter
Plain-English definitions for the 5 terms you'll see in any quote, certificate or enforcement notice for CDM 2015 Construction Regulations.
- Construction (Design and Management) Regulations 2015CDM 2015
- The principal UK construction H&S regulation — applies to every construction project regardless of size.
- Principal DesignerPD
- Statutory CDM role — coordinates H&S in the design phase. Required where there is more than one contractor.
- Principal ContractorPC
- Statutory CDM role — coordinates H&S in the construction phase. Required where there is more than one contractor.
- Construction Phase PlanCPP
- The H&S plan for the construction phase. Mandatory for every CDM project; lighter for domestic + non-notifiable.
- F10 NotificationF10
- Form filed with HSE for notifiable projects — over 30 working days with 20+ workers, or over 500 person-days. Filed by the principal contractor (or client if no PC).
How CDM 2015 applies to a domestic extension
Five steps from instruction to certificate. Total time: 12w.
01
Confirm CDM applies
Day 0
Every UK construction project is in scope. Even single-trade jobs over a few days have basic CDM duties — RAMS, competence, welfare facilities.
02
Domestic client = light duties
Day 0
As a homeowner your duties pass to the contractor (CDM Reg 7). You appoint a competent contractor; they take Principal Contractor + Principal Designer duties.
03
Multiple contractors?
Day 0
If 2+ contractors are working on site simultaneously, you must formally appoint a Principal Designer and Principal Contractor in writing.
04
Notifiable threshold
Pre-start
If project is over 30 working days with 20+ workers OR over 500 person-days, the PC submits F10 to HSE before work starts. Display F10 on site.
05
Construction Phase Plan
Pre-start
Every project has a CPP. Domestic + non-notifiable can be 1 page — risk register, RAMS, welfare arrangements, emergency contacts. PC produces.
CDM 2015 Construction Regulations. Done compliant.
Every TradeMatch-listed tradesperson covering CDM 2015 Construction Regulations carries the relevant scheme registration. Verified at onboarding, re-verified annually, certificates posted to you within 30 days of any notifiable work.
CDM 2015 — what triggers what
Side-by-side comparison of the compliant route versus the unregistered shortcut. Most rows trace a straight line from regulation to financial exposure.
| Project type | F10 notification? | PD + PC required? | CPP required? |
|---|---|---|---|
| COMPLIANT — RECOMMENDEDSingle contractor, < 30 days | No | No | Yes — light |
| 2+ contractors, < 30 days | No | Yes — written appointment | Yes — light |
| Project > 30 days + 20 workers OR > 500 person-days | Yes — F10 to HSE | Yes — written appointment | Yes — full |
| Domestic client, single contractor | No | No | Yes — light |
| Domestic client, 2+ contractors | Threshold-dependent | Yes — passes to contractor | Yes |
Source: HSE L153 Managing health and safety in construction 2015.
The questions homeowners ask before they commit.
Do I have CDM duties as a homeowner?
Yes, but light. Under CDM Reg 7 your domestic-client duties pass to the contractor — you appoint a competent contractor, they take Principal Contractor and Principal Designer duties. Make sure the appointment is in writing (it can be a clause in the quote) and that the contractor produces a Construction Phase Plan before tools touch site.
When is a project F10 notifiable?
Over 30 working days AND with more than 20 workers simultaneously at any point, OR over 500 person-days total. The principal contractor submits the F10 to HSE before work starts. Display the F10 visibly on site.
Who is the Principal Contractor on a domestic extension?
Where the homeowner uses one builder, the builder is automatically PC. Where there are 2+ contractors, the homeowner must formally appoint a PC in writing — typically the main builder. The PC takes responsibility for all H&S coordination during the construction phase.
What is a Construction Phase Plan?
The H&S plan for the construction phase — risk register, RAMS, welfare arrangements, emergency contacts, materials handling, working at height, asbestos handling. For domestic + non-notifiable jobs it can be 1–2 pages; for notifiable jobs it's a full document. Produced by the Principal Contractor before work starts.
Is asbestos work covered by CDM?
CDM applies to construction work; CAR 2012 separately governs asbestos. They overlap — CDM's pre-construction information must include asbestos status (R&D survey results), and the asbestos contractor must be CAR 2012 compliant within the CDM-managed project.
What's the fine for CDM breach?
HSE prosecutions average £100k for serious CDM breaches; fatal incidents can run £500k+ plus director-level prosecution. Domestic clients are rarely prosecuted (duties pass to contractor); non-domestic clients face full duty exposure. The HSE construction inspectorate runs ~5,000 site visits annually.
Going deeper.
CDM-compliant construction.
TradeMatch builders carry full CDM 2015 + CHAS / SafeContractor evidence. CPP, RAMS and F10 notification handled where required.