Construction compliance guide
F10 Notification: HSE Thresholds + How to Submit (2026)
A plain-English guide to F10 notifications for UK builders. When your project is notifiable, what goes in the form, and how to stay on the right side of the HSE.
TL;DR
A plain-English guide to F10 notifications for UK builders. When your project is notifiable, what goes in the form, and how to stay on the right side of the HSE.
F10 quick check
Is my project notifiable?
Enter your planned programme and worker numbers. Under CDM 2015, an F10 is required if the job lasts more than 30 working days with more than 20 workers on site at any point, or if it exceeds 500 person-days.
Estimated person-days: 120
Likely not notifiable: an F10 is probably not needed on these figures.
This is a planning check, not legal advice. If the programme changes, rerun the calculation and keep your CPP up to date.
No F10 needed on these figures — but every construction project still needs a construction phase plan. The Site Book generates yours from your project details.
See how →Notifiable project? You'll need a Construction Phase Plan too
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What is an F10 form?
The F10 is the notification form required under Regulation 6 of the Construction (Design and Management) Regulations 2015 — commonly known as CDM 2015. If a project is forecast to be notifiable before construction starts, the duty holder must ensure this form is submitted to the Health and Safety Executive (HSE) as soon as practicable before the construction phase begins. If a revised forecast first makes it notifiable after work starts, the duty holder must notify HSE as soon as practicable then.
The commercial client holds the regulation 6 duty. On a domestic project it passes to the contractor where there is only one contractor, or to the principal contractor where there is more than one contractor, unless a principal designer agrees in writing to fulfil it. Someone else may submit or display the F10 on the duty holder’s behalf without taking over the legal duty.
The purpose is straightforward: it tells the HSE who is involved in the project, what the work is, where it is happening, and when it starts and finishes. Think of it as the HSE’s register of significant construction projects across Great Britain. It means the regulator knows the work is happening and can plan inspections or respond to incidents with the right context.
The F10 is not a safety plan — it does not replace your Construction Phase Plan or your risk assessments. It is purely a notification. Failing to submit one when the regulation 6 duty applies is a breach of CDM 2015.
When is a project notifiable?
Not every construction project needs an F10. A project is notifiable to the HSE if it meets either of two thresholds:
- Threshold 1: The construction work will last longer than 30 working days AND will have more than 20 workers on site at any one time.
- Threshold 2: The construction work will exceed 500 person-days.
A “person-day” is simply the number of workers multiplied by the number of days they work. If you have 10 workers on site for 50 days, that is 500 person-days. If you have 5 workers for 100 days, that is also 500 person-days.
Example 1: A 6-week rear extension with 3 workers on site. That is 30 working days × 3 workers = 90 person-days. It does not exceed 500 person-days, and you never have more than 20 workers on site. This project is not notifiable.
Example 2: A new-build house with 25 workers over 8 weeks (40 working days). That is 25 × 40 = 1,000 person-days. It exceeds 500 person-days, and you have more than 20 workers on site for more than 30 days. This project is notifiable on both counts.
What information goes in the F10?
The F10 form asks for the key facts about your project. There are no trick questions — if you know the job, you know the answers:
Project address
The full address of the construction site where the work will take place.
Client name and address
The name and contact details of the person or organisation commissioning the work. On a domestic project, this is the homeowner.
Principal designer
The name, address, and contact details of the principal designer appointed under CDM 2015. If there is only one contractor and no principal designer has been appointed, this can be left blank.
Principal contractor
The name, address, and contact details of the principal contractor. If you are the only contractor, you fill in your own details here.
Start date and planned duration
When construction work is expected to begin on site, and how long the project is planned to last.
Estimated maximum workers
The maximum number of people you expect to be working on site at any one time during the project.
Brief description of work
A short summary of the construction work being carried out — for example, “new-build 4-bedroom detached house” or “commercial office refurbishment across 3 floors.”
The F10 can be submitted online via the HSE’s official notification portal. Gather the project and duty-holder details before opening the form.
The duty holder must also ensure an up-to-date copy is clearly displayed in the construction site office in a form workers can read. They may ask the principal contractor or contractor to display it on their behalf.
What happens if you don’t notify?
If the regulation 6 duty holder fails to notify HSE when a project is notifiable, that is a breach of CDM 2015 Regulation 6. The HSE takes this seriously, and the consequences can be significant:
- Improvement notices: The HSE can require the duty holder to submit the notification within a set timeframe and demonstrate that proper CDM arrangements are in place.
- Prohibition notices: In serious cases, the HSE can stop work on site until compliance is achieved. That means workers standing idle while you sort out paperwork.
- Prosecution: For persistent or serious breaches, the HSE can prosecute. Fines for CDM offences can be substantial, and a conviction goes on your record.
Beyond the formal enforcement, there is a practical issue: if there is an incident and the required F10 was not submitted, the HSE will ask the regulation 6 duty holder why. A missing notification suggests the project was not being properly managed under CDM 2015, which raises questions about everything else — your Construction Phase Plan, your risk assessments, your site management. It puts you on the back foot from the start of any investigation.
How The Site Book auto-detects notifiability
Working out whether your project crosses a notification threshold is not difficult — but it is easy to overlook, especially when you are busy pricing jobs and ordering materials. That is where The Site Book helps.
When you create a project in The Site Book and enter the expected duration, number of workers, and trades involved, the system automatically calculates whether your project crosses either notification threshold. It checks the 30-day / 20-worker rule and the 500 person-day rule simultaneously.
If your project is notifiable, you get a clear alert with guidance on what to do next — including a reminder that the duty holder, or someone acting on their behalf, must submit the F10 at the time regulation 6 requires. If it is not notifiable, the system confirms that too, so you can focus on the job without second-guessing the regulations.
It is one less thing to worry about. The maths happens in the background, and you get a straight answer: notifiable, or not notifiable. No spreadsheets, no manual calculations, no guesswork.
Frequently asked questions
Who is responsible for submitting the F10?
Under CDM 2015, the client is responsible for notifying the HSE. On commercial projects, this duty sits with the commercial client — even when the principal contractor or principal designer submits the form on their behalf, the legal duty remains with the commercial client. On domestic projects, the client’s duties — including notification — transfer automatically to the contractor (if there’s only one contractor) or the principal contractor (if there’s more than one contractor) — or, where there is more than one contractor, instead to the principal designer if there’s a written agreement that they’ll take on those duties. There is no separate duty-transfer agreement for a principal contractor; a principal contractor already receives these duties by default whenever more than one contractor is involved — though the principal contractor's own appointment must still be made in writing under regulation 5, separately from that question. If the client never makes that appointment on a job with more than one contractor, regulation 7(2) deems whichever contractor is in control of the construction phase to be the principal contractor instead — a sole contractor holds the duties directly under regulation 7(1)(a), with no principal contractor role to deem. Whichever party the duties transfer to on a domestic project holds the notification duty itself — it does not remain with the domestic client.
When should the F10 be submitted?
If a project is forecast to be notifiable before construction starts, whoever holds the regulation 6 duty must ensure the F10 is submitted to HSE as soon as practicable before the construction phase begins. If a revised forecast first makes the project notifiable after work starts, the duty holder must notify HSE as soon as practicable then. The commercial client holds the duty; on a domestic project it passes to the contractor where there is only one contractor, and where there is more than one contractor to the principal contractor, or, where there is more than one contractor, to the principal designer if there is a written agreement to that effect. Someone else may submit on the duty holder's behalf without taking over the legal duty.
Can you update an F10 after it has been submitted?
Yes. The regulation 6 duty holder must ensure the notice is updated if necessary and that an up-to-date copy is displayed in the construction site office where workers can read it. The duty holder, or someone acting on their behalf, can submit an update through the HSE portal.
What if the project details change mid-build?
If a revised programme or workforce forecast makes a project notifiable — more than 30 working days with over 20 workers simultaneously, or over 500 person-days — the regulation 6 duty holder must notify HSE as soon as practicable. The duty holder must also ensure the notice is updated if necessary, including when relevant project details change.
Do domestic projects need an F10?
A domestic project is notifiable on the same thresholds as any other project: scheduled for more than 30 working days with over 20 workers simultaneously, or over 500 person-days. If it is notifiable, the regulation 6 duty passes to the only contractor on a single-contractor project; on a multi-contractor project it passes to the principal contractor, or, where there is more than one contractor, to the principal designer if there is a written agreement to that effect.
F10 notification — what builders need to know
Pros
- The F10 is a short online form — most of it you already know from your CPP (client, PD, PC, dates).
- Submitting is free, same-day, and the HSE acknowledgement gives you evidence of compliance.
- Updating an F10 mid-project is easy and incurs no penalty — the HSE expects programmes to evolve.
- Knowing the 30-day / 20-worker / 500-person-day thresholds lets you spot notifiability at quote stage, not crisis stage.
Cons
- For a project already forecast to be notifiable, the duty holder breaches regulation 6 by starting construction before notifying HSE.
- The 500 person-day limb can make a project notifiable even when the 30-day and 20-worker limb is not met.
- Commercial: client keeps F10 duty when another files. Domestic: contractor if only one contractor; PC if more than one contractor; or, if more than one contractor, PD by written agreement.
- A non-notifiable project still needs a CPP — skipping one because you did not need an F10 is a separate breach.
| Threshold | Duration | Workers on site | Person-days total |
|---|---|---|---|
| Threshold 1 | >30 working days | >20 at any one time | — |
| Threshold 2 | — | — | >500 |
| Small kitchen refit | <30 days | 1–3 | ~20 |
| Standard single-storey extension | <30 days typically | 2–4 | ~40–60 |
| Large two-storey extension | May exceed 30 days | 5–8 | 100+ |
| Major refurb with trades overlapping | Often >30 days | >20 at peak | Often >500 |
“A project is notifiable if the construction work on a construction site is scheduled to last longer than 30 working days and have more than 20 workers working simultaneously at any point in the project; or exceed 500 person days.”
Get your project paperwork sorted
Filing an F10? The Site Book creates the CPP and RAMS that go alongside your notification.
Need a Construction Phase Plan too?
If your project is notifiable, you definitely need a CPP. Even if it is not notifiable, CDM 2015 still requires one. Describe your project and get a project-specific plan drafted.
Keep your CDM paperwork organised without the headache.
The Site Book creates your Construction Phase Plan and keeps your CDM paperwork in one place. On Pro it also pre-fills the F10. No credit card required.
Sources
- CDM 2015 — Notification of construction projects (F10) — HSE · Accessed 17 April 2026