Principal designer
Does a house extension need a CDM principal designer?
Short answer
Usually yes. CDM 2015 applies to domestic building work, and the test is whether the project will involve more than one contractor. Most extensions do: a builder plus an electrician, a groundworker, a roofer or a gas engineer is already more than one. Where that is the case, regulation 5 requires the client to appoint a principal designer and a principal contractor in writing before the construction phase begins, whatever the value of the work.
Why extensions almost always qualify
Think about who actually turns up on a single storey rear extension. Groundworks. A steel fabricator or a beam supplier. The main builder. A roofer for the flat roof. An electrician for the new circuits and the consumer unit. Possibly a gas engineer for a moved boiler. A plasterer. A window installer.
Even if the main builder covers several of those, one subcontracted trade is enough. They do not need to be on site at the same time. More on how that test works.
What actually changes on a domestic project
Not whether CDM applies. It does. What changes is who carries the client duties.
Regulation 7(1) moves the client duties in regulations 4(1) to (7) and 6 onto the contractor on a single contractor project, or onto the principal contractor where there is more than one, unless there is a written agreement for the principal designer to take them. So a homeowner does not personally carry the full set of client duties a business would. What the homeowner does carry is the appointment: regulation 5 is not in the list that transfers.
And if nobody is appointed, regulation 7(2) fills the gap by default: the designer in control of the pre-construction phase becomes the principal designer, and the contractor in control of the construction phase becomes the principal contractor.
What the appointment involves on an extension
Less than most people expect. On a typical extension:
- One short form from you
What you know about the house, how you will be living in it during the works, access, and any paperwork you hold.
- One short form per designer
Your architectural designer and, where there is one, your structural engineer. Around ten minutes each.
- One site visit
To record the building as it is rather than as the drawings assume.
- The pre-construction information pack
Out to whoever is pricing and whoever is building, before work starts.
What that produces for the builder is worth more than the paperwork suggests: the asbestos position for a house of the right age, the propping sequence for the wall coming out, whether anyone is living in the house during the works, and what the access actually is.
What it costs
ClearCDM prices an extension, loft conversion or refurbishment of a single dwelling from £750 plus VAT for the pre-construction service, with the construction phase from £450 plus VAT on top if you want the appointment to run to completion and the health and safety file handed over at the end. The published fee schedule, or price your own project.
What happens if you skip it
The duties do not disappear, they land on people who have not priced for them. On a domestic project that means your builder becomes the principal contractor and picks up your client duties as well, and your designer becomes the principal designer, in both cases usually without knowing. Meanwhile the work the role exists to do, gathering the information and coordinating the design risks, does not happen at all, and the first anyone hears about the buried service or the unpropped wall is when it is uncovered.
Sources
- CDM 2015, regulation 5: appointment of the principal designer and the principal contractor legislation.gov.uk
- CDM 2015, regulation 7: application to domestic clients legislation.gov.uk
- HSE: domestic clients, roles and responsibilities hse.gov.uk
- Managing health and safety in construction, L153 HSE guidance on the Regulations
Find out where your project stands
The free checker asks six questions and tells you whether the appointment is required, and why.
Open the checker →Not sure yet? go straight to a fixed fee.