When do you need to notify the HSE? The F10 explained

The F10 is the HSE (Health and Safety Executive) notification form for construction projects. Submitting it is a legal requirement under CDM 2015, but only for certain projects. Knowing whether your project triggers this requirement is one of the first things you need to work out before breaking ground.

When is a project notifiable?

A construction project must be notified to the HSE if it will:

• Last more than 30 working days and have more than 20 workers working simultaneously at any point, or
• Exceed 500 person-days of construction work

The first test has two parts: both the duration and the headcount must be met. The second test (500 person-days) applies regardless of daily headcount.

Person-days means the total number of working days across all workers. So a 10-person crew working for 50 days equals 500 person-days, which is right at the threshold. A 5-person crew working for 100 days is also 500 person-days. Any number above that triggers the requirement.

It is worth noting that these thresholds are based on planned work, not actual. You assess notifiability at the start, based on your best estimate. If circumstances change and the project grows beyond the thresholds, you should notify at that point if you have not already done so.

Common scenarios

Here are some practical examples to make this concrete:

• A 6-week house extension with 3 workers: Not notifiable. Under 20 simultaneous workers and under 500 person-days (3 workers x 30 days = 90 person-days).
• A 12-week commercial fit-out with 25 workers: Likely notifiable. Over 30 working days with more than 20 simultaneous workers.
• A 4-month school refurbishment with 8 workers: Check the person-days. 8 workers x 80 working days = 640 person-days. Notifiable.
• A 3-week emergency repair with 30 workers: Not notifiable under the first test (under 30 working days), but check person-days. 30 x 15 = 450. Just under the threshold. Not notifiable.

When in doubt, notify. There is no penalty for notifying a project that turns out to be under the threshold. There are real penalties for missing a notification on a project that needed one.

Domestic projects

On domestic projects (work on someone's private home), the client's CDM duties transfer to the contractor. This includes the duty to notify if the thresholds are met. In practice, most domestic projects are small enough that they are not notifiable. But large domestic builds, loft conversions with structural work, or multi-trade refurbishments can creep over the threshold. Do the calculation.

What the F10 contains

The F10 form collects:

• Project address and description of the work
• Expected start date and planned duration
• Principal contractor name and contact details
• Principal designer name and contact details
• Estimated maximum number of workers on site at any one time
• Number of contractors expected on the project

The form itself is straightforward. The information it asks for is data you should already have from your project planning.

When does it need to be submitted?

The F10 must be submitted as early as practicable before the construction phase begins. Not on day one of work. Earlier is better. The HSE expects to receive the notification during the planning stage, giving them time to assess whether the project warrants a site visit.

In practice, submit the F10 as soon as you have confirmed the project details and appointed the principal designer. There is no minimum lead time, but leaving it until the day before work starts is cutting it unnecessarily close.

What happens if you miss it?

Failing to submit an F10 on a notifiable project is a breach of CDM 2015. The HSE can issue an improvement notice, and in serious cases, prosecute. Fines for CDM breaches are unlimited.

Beyond the fine itself, there is a practical problem. If the HSE carries out a site visit and finds no F10 on a notifiable project, it immediately signals that your CDM compliance may be lacking across the board. The visit is unlikely to end with a friendly chat. Missing a notification is a red flag that often leads to a deeper inspection of your CPP, RAMS, site inductions, and other documentation.

How The Site Book helps

The Site Book runs the notifiability check automatically from your project data. When you enter the expected duration, number of contractors, and peak headcount, the system calculates whether the project is notifiable and flags it clearly on the project dashboard.

If your project is notifiable, the F10 form is pre-filled with your project details, principal contractor information, and principal designer details. You review it, confirm it is correct, and you are done. No manual form-filling, no guessing at the thresholds, no risk of forgetting.