When a job becomes notifiable,
and who tells the HSE.

A project is notifiable under CDM 2015 if the construction work is scheduled to last longer than 30 working days and have more than 20 workers working simultaneously at any point, or if it exceeds 500 person days. Either limb triggers it. The client gives the notice, on form F10, as soon as practicable before the construction phase begins.

When does a job become notifiable to the HSE?

Regulation 6 sets two alternative thresholds, and the structure matters because it is stated wrongly in a lot of places.

1. Longer than 30 working days AND more than 20 workers working simultaneously at any point on the project. Both parts of this limb have to be met. A six month job with a gang of eight never satisfies it.
2. OR the work exceeds 500 person days. This limb stands alone. A short, heavily manned job can cross it without ever having 20 people on at once for 30 days.

So the connector between the two limbs is or, and the connector inside the first limb is and. Getting that the wrong way round is the commonest error, and it produces both false positives and false negatives.

Person days is simply the total of days worked by all workers on the construction phase. Ten people for fifty days is 500, which is not more than 500, so it does not cross. Ten people for fifty one days does.

Either threshold on its own is enough. Plenty of jobs are notifiable on person days while never coming close to twenty people on site at once.

Notifiable is not the same as needing a principal contractor

This is the confusion worth clearing, because the two questions get merged constantly and they have nothing to do with each other.

Needing a principal contractor turns on the number of contractors: more than one, or reasonably foreseeably more than one, and the duty attaches regardless of size or duration.

Being notifiable turns on duration and workforce size, and says nothing about how many contractors are involved.

Which produces four possible combinations, and all four occur. A small refurbishment with a builder and an electrician needs a principal contractor and is not notifiable, and that combination is extremely common. A long single-contractor job could in principle be notifiable without triggering the appointment requirement. Answer the two questions separately, in that order, and the paperwork follows. The appointment side is covered in when you become the principal contractor, and when you do not.

Who submits the F10, and when?

The client. Not the principal contractor, not the principal designer, and not you.

The notice must be given as soon as practicable before the construction phase begins, and it goes to the HSE, except on railway, nuclear or defence sites where it goes to the relevant authority instead.

Two practical consequences of the duty sitting with the client. First, on domestic and small commercial work the client frequently has no idea this is their job, so somebody has to tell them, and that somebody is usually you. Second, the notice is often prepared in practice by the principal contractor or principal designer on the client's behalf, which is fine, but it does not move the duty. It remains the client's.

What the notice does, and what it does not

It tells the regulator that a project of a certain size is happening, with the particulars listed in Schedule 1: the address, the client, the duty holders, the planned dates, the expected number of workers and contractors, and who is on site.

It has to be displayed in the construction site office in a comprehensible form, and updated if the particulars change materially. That display requirement is routinely forgotten, and it is one of the easiest things for an inspector to notice on arrival.

What it does not do is any of the things people fear or hope. It does not summon an inspection, it is not an application for anything, nothing has to be approved, and there is no fee. It also does not change any of your duties: a notifiable project carries exactly the same CDM obligations as a non-notifiable one of the same shape. Notification is administrative.

If it should have been notified and was not

It is a breach of regulation 6 by the client. The practical position for a contractor who realises mid-job is straightforward: raise it in writing with the client, and get it submitted. Late notification is considerably better than none, and a contemporaneous email showing you raised it is worth having if the matter is ever looked at.

The reason to bother, beyond the regulation, is that an unnotified notifiable project is an obvious signal to an inspector that the project's management arrangements were not thought about, which colours everything they look at afterwards.

Where to start, on Monday

Take each job on your board and answer two questions, in this order. Is there more than one contractor on it, which decides the appointment. And does it cross either notification threshold, which decides the F10.

For the second, the person days arithmetic is usually the quicker route: total the days you expect each trade to be on site and add them up. Where the answer is close to 500, treat it as notifiable, because the cost of notifying a job that turned out not to need it is nothing and the cost of the reverse is not.

Then, on any job that is notified, walk into the site office and check the notice is actually displayed.