A construction project becomes "notifiable" when it crosses specific thresholds under CDM 2015. When that happens, the client must send written notice to the HSE before the construction phase begins — this is the F10 notification.
The F10 is not an application for permission. HSE does not need to approve the project. The purpose is to put the regulator on notice that a project of significant size or duration is starting, so they can allocate inspection resource appropriately. But submitting it incorrectly, or failing to submit it at all, is a breach of the Construction (Design and Management) Regulations 2015 (SI 2015/51).
When does a project become notifiable?
Regulation 6(1) of CDM 2015 sets out the notifiable threshold. A project requires an F10 notification if the construction work on the site is expected to:
(a) last longer than 30 working days AND have more than 20 workers working simultaneously at any point during the project, OR
(b) exceed 500 person-days of construction work
These are alternative tests — a project is notifiable if it meets either condition. Both thresholds must be assessed in advance. If a project is expected to exceed 500 person-days but the peak workforce never exceeds 20 workers simultaneously, it is still notifiable under (b).
How to calculate person-days
Person-days is the total number of workers multiplied by the number of working days each works on the project. A project with 5 workers working 5 days a week for 22 weeks is 5 × 110 = 550 person-days — notifiable under condition (b) even if only 5 workers are ever on site at once.
The calculation should use expected figures. Where a project spans several phases with varying workforce levels, add the person-days across all phases. It is the client's responsibility to assess whether the project is notifiable — in practice, this assessment is often carried out by the principal designer or principal contractor on the client's behalf.
What counts as construction work
CDM 2015 Regulation 2 defines construction work broadly. It includes building, civil engineering, alteration, conversion, fitting out, commissioning, renovation, repair, upkeep, redecoration, demolition, and dismantling. It includes maintenance of fixed plant and structures. It also includes site preparation, excavation, and the installation and commissioning of mechanical, electrical and M&E systems.
Excluded from the definition: the exploration for, or extraction of, mineral resources, and any preparatory activities carried out at a place where such exploration or extraction is carried out. This is the only exclusion stated in the Regulation 2 definition.
Who sends the F10 and when
The obligation to notify rests with the client, and the notification must be given to HSE "as soon as practicable before the construction phase begins" (Regulation 6(2)).
In practice, the principal designer or principal contractor typically completes the F10 form on the client's behalf. The client must approve and sign the declaration before it is submitted.
"As soon as practicable before the construction phase begins" has been interpreted by HSE as meaning the notification should be submitted before any construction work starts on site — not on the day work begins. For larger projects, submitting 2-4 weeks before site start is good practice.
What the F10 must contain
Schedule 1 of CDM 2015 prescribes the information that must be included in the notification. The 15 required particulars are:
- Date the notice is forwarded to HSE
- Address or precise location of the construction site
- Name of the local authority where the site is located
- Description of the project and the construction work
- Client name, address, telephone number, and email (if available)
- Principal designer name, address, telephone number, and email
- Principal contractor name, address, telephone number, and email
- Planned date for the start of the construction phase
- Time allocated by the client for the construction work
- Planned duration of the construction phase
- Estimated maximum number of people working on the site simultaneously
- Planned number of contractors on the site
- Names and addresses of any contractors already appointed
- Names and addresses of any designers already appointed
- A declaration signed by or on behalf of the client confirming they are aware of their duties under CDM 2015
The notification does not need to be final on all points at the time of submission — for example, not all contractors will necessarily be appointed before the construction phase begins. However, the information provided must be accurate at the time of submission, and the notification should be updated if circumstances change materially.
How to submit
HSE provides an online notification service for F10 submissions. The current form is available at:
www.hse.gov.uk/forms/notification/f10.htm
Submissions can be made online. HSE does not charge a fee for notification. On submission, you should retain a copy — HSE does not automatically issue confirmation receipts in all cases, and you may need evidence of submission if the project is inspected.
The notification must also be displayed on site. Regulation 6(3) requires that the particulars of the notice are "clearly displayed in the construction site office in a comprehensible form where it can be read by any worker." This is typically done by printing the F10 confirmation and posting it in the site office.
For projects involving work on a nuclear site or a work site controlled by the Ministry of Defence, the notification goes to the Office for Nuclear Regulation or equivalent defence authority rather than HSE (Regulation 6(5)).
What the F10 is not
The F10 notification is often confused with other CDM documents. Some clarifications:
The F10 is not the construction phase plan. The construction phase plan is a separate document that the principal contractor must prepare before construction begins (Regulation 12). A notifiable project needs both. See our guide to construction phase plans.
The F10 is not proof of CDM compliance. Submitting an F10 does not demonstrate that the project is being managed safely. It simply puts HSE on notice. HSE's inspection priorities are set separately from whether an F10 has been submitted.
The F10 is not a one-time document. If the project changes significantly after notification — new principal contractor, different site address, substantially different duration — the notification should be updated by resubmitting via the HSE form.
Non-notifiable projects still require CDM compliance. Every construction project in Great Britain is subject to CDM 2015, regardless of size. The F10 threshold determines notification, not whether CDM applies.
If a project crosses the threshold during construction
Sometimes a project that was not initially notifiable becomes notifiable as scope increases. If the actual or expected size of the project crosses either threshold during the construction phase, the client should submit an F10 as soon as the project becomes notifiable — even if construction has already started.
Common mistakes
Miscounting person-days. The 500 person-days threshold is the one most commonly underestimated. Small-to-medium refurbishments with extended programmes frequently cross it without being obviously large projects.
Submitting too late. Notification submitted on the first day of construction is technically non-compliant. HSE expects notification before work starts.
Omitting the client declaration. Without a signed client declaration, the F10 is incomplete (Schedule 1, item 15). The declaration confirms the client understands their CDM duties.
Not displaying the notice on site. The printed F10 must be visible to all workers in the site office from day one.
Treating the F10 as the start of CDM. CDM obligations for the client, principal designer, and principal contractor begin before the F10 is submitted. Appointment of a principal designer, provision of pre-construction information, and preparation of the construction phase plan all happen before or alongside the F10 notification — not after it.
For the full picture of what the client is required to do on a notifiable project, see our guide to CDM client duties.
Sources
- The Construction (Design and Management) Regulations 2015 (SI 2015/51), Regulations 2, 6, Schedule 1
- HSE F10 notification form
- HSE — CDM 2015 guidance
- HSE L153 — Managing health and safety in construction
This guide is for informational purposes and does not constitute legal advice. For project-specific CDM compliance questions, consult a qualified health and safety professional.
Last reviewed: 15 July 2026