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16th July, 2019

How To Calculate If Your Construction Project Is CDM Notifiable

Under the Construction (Design & Management) Regulations 2015 (CDM), certain construction projects need to be notified to the HSE. This notification is a legal requirement and needs to be done before work starts on site. In this blog post, we are going to look at when your project is notifiable, and how to calculate if you meet the threshold.

When is a construction project notifiable?

First, let's look at what the regulations say...

6.—(1) A project is notifiable if the construction work on a construction site is scheduled to—

  1. last longer than 30 working days and have more than 20 workers working simultaneously at any point in the project; or
  2. exceed 500 person days.
The Construction (Design and Management) Regulations 2015 Notification

This shows us that there are two thresholds for notification. If your project lasts over 30 days with more than 20 workers at any time, or, has over 500 person days. Meet either of these criteria, and your construction project needs to be notified.

Just want to know if your project is notifiable? Use our free CDM 2015 notification calculator.

Under CDM 2015 the rules regarding notification requirements have changed, and the changes may be subtle but they can have a big impact on your project. These changes affect a large number of projects, so it is important to be aware of the notification terms so you don't get caught out. Before we get into calculating working days and person days, let's make sure we know how the changes affect your project.

Notification Change 1: Domestic Projects

Domestic projects, or to be precise, projects with domestic clients (having work done on their own homes - not related to any business) were always exempt from notification under CDM 2007.

Not so under 2015.

If you meet the notification threshold, the HSE want to hear from you, regardless of the type of project.

Notification Change 2: Notification Affects Duties

Notifiable projects used to trigger additional duties, or, to be more accurate - there were fewer duties under CDM on non-notifiable projects.

This has now changed under CDM 2015.

All projects with more than one contractor (including subcontractors) now require the appointment of duty holders and documentation such as Construction Phase Plans to be produced.

Notification Change 3: 30 Days or not 30 Days

Projects over 30 working days were always notifiable before, but this is not quite the case under CDM 2015.

The 30-day threshold still stands, but only if you will have over 20 workers on site any one time. Remember, that's at any point, so you could trigger the requirement on day one or day 27.

As before, 30 working days includes part days and weekends if you are working them.

Notification Change 4: 500 Person Days Matters

Ok, ok, this is not a change as such. However, the 500 person days rule was largely ignored previously because the 30-day trigger was usually activated before projects were even close to 500 person days. Not so anymore.

Now, if you only plan on having 10 people on site, the 30-day rule won't ever apply to your project, but does that make it un-notifiable?


The 500 person day rule now matters way beyond the 30-day timeframe, so it is more likely to get triggered under CDM 2015.

If that 10 person a day project lasts longer than 50 days, the 500 person day rule will trigger the notification requirement.

Just want to know if your project is notifiable? Use our free CDM 2015 notification calculator.

How to calculate if your construction project is CDM notifiable

Ok, now we know that any construction project can be notifiable, how do we calculate if your project needs to be notified? Well, you can cheat and use our free CDM notification calculator, or you can keep reading.

The first part is pretty easy to get your head around, 30 working days with more than 20 workers at any point.

It is important to remember that working days includes "any day on which construction work takes place", so this would include weekends if work is carried out on a Saturday or Sunday. And, even if work is only carried out for part of the day, this should be considered a full working day in your calculation.

“working day” means any day on which construction work takes place;

The Construction (Design and Management) Regulations 2015 Interpretation

But what about the second part? Exceeds 500 person days, how do we calculate that? If you are only ever going to have less than 20 workers on site, this is the notification threshold you should be considering.

Does your project exceed 500 person days?

To calculate this you need to consider how many people you will have on site, and then multiply that by the number of days they will be on site.

10 people working for 60 days? 10 x 60 = 600 person days. This project is notifiable.

5 people working for 102 days? 5 x 102 = 510 person days. This project is notifiable.

2 people working for 20 days? 2 x 20 = 40 person days. This project is not notifiable.

Remember that any day work takes place is classed as a working day. If you work Monday morning, and Tuesday afternoon, that might be less than 8 hours work total, but it is still 2 working day. For the purposes of your CDM notification calculation, any day where work takes place, even just for a short time, is a working day.

Be aware, however, that unlike CDM 2007, under CDM 2015, the notification status of your project no longer triggers additional duties. If your project is non-notifiable, you still must comply with all the other duties under CDM 2015, the only difference being you don't have to complete the F10 notification form.

Need help with CDM? You can use the free CDM duty holder guides to get up to speed with all the requirements.

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This article was written by Emma at HASpod. Emma has over 10 years experience in health and safety and BSc (Hons) Construction Management. She is NEBOSH qualified and Tech IOSH.

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