A construction project is notifiable under the Construction (Design and Management) Regulations 2015 if the construction work is scheduled to last more than 30 working days and have more than 20 workers working simultaneously at any point, or if it is scheduled to exceed 500 person-days. Those are two separate tests. A project does not need to pass both. Meeting either threshold makes the project notifiable, but being below both thresholds does not mean CDM 2015 stops applying.
Construction works at 171 Victoria Street, London, photographed in September 2026. CDM 2015 applies across construction projects, while an F10 notification is required only where the Regulation 6 notification thresholds are met. Image: London Construction Magazine.
F10 quick test
Test 1: More than 30 working days AND more than 20 workers working simultaneously at any point?
Test 2: More than 500 person-days of construction work?
If either answer is yes, the project is notifiable.
If either answer is yes, the project is notifiable.
The distinction matters because notification is often confused with the wider CDM regime. As LCM explains in its guide to when CDM Regulations apply to construction projects, notification is a scale threshold within CDM rather than the trigger that makes CDM duties exist.
The two F10 thresholds under CDM 2015
Regulation 6 of the Construction (Design and Management) Regulations 2015 sets out the notification test. The wording is based on what the construction work is scheduled to involve, so project teams should assess notification during planning rather than wait until labour or programme numbers have already crossed the threshold.
| Test | Threshold | What matters |
|---|---|---|
| Duration and workforce | More than 30 working days and more than 20 workers simultaneously at any point | Both parts of this test must be satisfied. |
| Total volume of work | More than 500 person-days | This is an independent trigger. The project does not also need 20 workers. |
The word and in the first test is critical. A 40-working-day project with four workers does not become notifiable merely because it exceeds 30 days. Equally, a ten-day fit-out with 25 workers does not satisfy that first test because the project does not exceed 30 working days. Both examples must still be checked against the separate 500 person-day threshold.
Working days include weekends if construction work takes place
The Health and Safety Executive's current CDM frequently asked questions clarify that every day on which construction work is likely to be carried out should be counted, including weekends and bank holidays. HSE also says the day should be counted even where the work taking place on that day is of short duration. That means the 30-working-day test should not automatically be calculated as six Monday-to-Friday weeks. A project operating on Saturdays, Sundays or bank holidays can accumulate working days more quickly. The same principle means project teams should not convert the 500 person-day threshold into an assumed number of labour hours. CDM uses person-days, not a 4,000-hour equivalent. The safest project assessment is therefore based on the expected construction programme, workforce forecast and actual days on which construction work will take place.
Five examples: is an F10 required?
The following simplified examples show why both tests need to be checked independently. Actual projects should use their full programme and workforce forecast rather than relying on an average headcount.
| Example | Programme | F10? | Reason |
|---|---|---|---|
| Office fit-out | 10 days × 25 workers = 250 person-days | No | More than 20 workers, but not more than 30 working days and below 500 person-days. |
| Warehouse refurbishment | 40 days × 4 workers = 160 person-days | No | Over 30 days, but not over 20 workers simultaneously and below 500 person-days. |
| Commercial refurbishment | 35 days × 15 workers = 525 person-days | Yes | The 500 person-day threshold is exceeded even though workforce numbers remain below 20. |
| 40-day project with one peak operation | Normally 8 workers, but 21 working simultaneously during one operation | Yes | The project exceeds 30 working days and has more than 20 workers simultaneously at one point. |
| Weekend infrastructure possession | 2 days × 110 workers = 220 person-days | No | Large workforce, but neither notification threshold is met in this simplified example. |
An F10 is not what makes CDM apply
One of the most persistent mistakes is treating a non-notifiable project as a non-CDM project. That is wrong. HSE's L153 guidance on managing health and safety in construction explains that CDM 2015 applies across the construction process, while notification under Regulation 6 only applies to projects meeting the additional scale tests. Where a project involves, or is reasonably foreseeable to involve, more than one contractor, the client must appoint a Principal Designer and Principal Contractor in writing. Those appointments arise from the number of contractors involved, not from whether an F10 is required. LCM's wider CDM Regulations guide explains the dutyholder structure, while the separate guide to Principal Contractor duties under CDM covers construction-phase control in more detail.
Who has to submit the F10?
For a commercial project, the statutory duty to notify rests with the client. HSE confirms that the client may ask somebody else to complete the notification on its behalf, but this does not transfer the client's Regulation 6 duty. The current HSE F10 service requires project information and contact details for the client, Principal Designer and Principal Contractor. Once submitted, the notification receives a unique serial number that can be used to retrieve and edit it.
There is also an important exception in how the form is completed. A single-contractor project can still be notifiable. HSE states that the client does not need to appoint a Principal Designer or Principal Contractor where only one contractor is involved, but its F10 form instructs users in that situation to enter the sole contractor in those fields and explain that it is a single-contractor project. For domestic clients, the position is different. HSE's domestic client guidance says client duties normally pass to the contractor on a single-contractor project or to the Principal Contractor where more than one contractor is involved. A Principal Designer can take on the domestic client's duties where this is agreed in writing.
What if the project becomes notifiable after work has started?
This is where programme monitoring becomes important. A job may be forecast below the thresholds at tender stage but later expand because of variations, additional work, delays or an increased workforce. HSE's L153 guidance deals directly with this situation. If a project was not initially notifiable but subsequent changes to its scope mean that it now meets the notification criteria, the client must notify the relevant enforcing authority as soon as possible.
LCM practical check: Do not assess F10 status once at mobilisation and forget it. Recheck the forecast when the programme extends, labour increases, additional packages are instructed or the construction sequence changes materially.
Regulation 6 also requires the notice to be periodically updated where necessary. HSE's online service allows an existing notification to be edited using its serial number and the relevant email address. The legislation does not set a universal rule such as "update the F10 whenever completion moves by seven days"; the practical requirement is to keep the notification accurate when material project information changes. A copy of the notification must also be clearly displayed in the construction site office in a form that workers can read.
F10 notification is not permission to start construction
An F10 is a statutory notification. It is not a construction permit, planning approval or building control approval. That distinction is particularly important on higher-risk building work in England. Building Safety Regulator guidance requires building control approval before relevant higher-risk building work starts. Submitting an F10 does not replace that approval process. A project can therefore be notifiable under CDM and still be waiting for another statutory approval before building work can legally begin. Equally, a project can fall below the F10 thresholds while other CDM and building control duties continue to apply.
F10 pre-start checklist
Before construction starts, the project team should be able to answer five basic questions:
1. How many working days is construction currently scheduled to take?
2. Will more than 20 workers be working simultaneously at any point?
3. What is the forecast total number of person-days across the construction phase?
4. Who holds the client duty to notify, including the domestic-client arrangements where applicable?
5. Is the programme being monitored so the notification position can be reassessed if scope or labour changes?
2. Will more than 20 workers be working simultaneously at any point?
3. What is the forecast total number of person-days across the construction phase?
4. Who holds the client duty to notify, including the domestic-client arrangements where applicable?
5. Is the programme being monitored so the notification position can be reassessed if scope or labour changes?
If the project meets either Regulation 6 threshold, the notification should be made to the relevant enforcing authority as soon as practicable before the construction phase begins. If a previously non-notifiable project later crosses the threshold because its scope changes, the notification should be made as soon as possible and kept updated thereafter.
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Expert Verification & Authorship: Mihai Chelmus Founder & Editor, London Construction Magazine | Construction Testing & Investigation Specialist |