Construction compliance guide
A plain-English guide to CPP requirements for house extensions under CDM 2015. When it’s legally required, what the domestic client rules mean for you, and how to produce one without the headache.
The Construction (Design and Management) Regulations 2015 — known as CDM 2015 — apply to all construction work in Great Britain. There is no minimum project value, no size threshold, and no exemption for domestic work. If you are carrying out construction work, CDM 2015 applies.
Regulation 12 is the one that matters here. It states that the construction phase must not begin until a construction phase plan has been drawn up. The wording is clear — it is not optional, it is not “if reasonably practicable,” and it is not limited to commercial projects. The construction phase plan must be in place before the first day on site.
Construction work is defined broadly in the regulations. It includes building, alteration, fitting-out, commissioning, renovation, repair, upkeep, decoration, demolition, and dismantling. A house extension falls squarely within this definition. Whether you are building a single-storey kitchen extension, a two-storey side return, or a loft conversion with a dormer, you are doing construction work and you need a CPP.
CDM 2015 recognises that a homeowner having an extension built is in a very different position to a property developer commissioning a block of flats. That is why the regulations include special provisions for domestic clients.
A domestic client is a person who has construction work carried out on their own home, or the home of a family member, and the work is not done in connection with a business. Most homeowners commissioning extensions, loft conversions, and renovations fall into this category.
Under Regulation 7, domestic clients do not have to carry out CDM client duties themselves. Instead, those duties transfer automatically to the contractor. If there is only one contractor on the project, all the client duties land on them. If there is a principal contractor appointed, the duties transfer to the principal contractor.
What does this mean for you as the builder? It means you cannot rely on the homeowner to sort out compliance. You are responsible for ensuring a CPP is produced before work begins, that welfare facilities are in place, and that health and safety is managed properly throughout the project. The homeowner’s only real duty is to pick a competent builder — everything else is on you.
There is one exception: a domestic client can choose to appoint a principal designer or principal contractor in writing. If they do, certain duties transfer to those appointees instead. This is uncommon on small domestic jobs but occasionally happens on larger extensions where an architect is already involved.
The short answer is: always. Every construction project needs a Construction Phase Plan before the construction phase begins. There is no lower threshold. A single-storey rear extension needs one. A loft conversion needs one. Even a straightforward bathroom refurbishment technically needs one.
The common confusion arises because builders mix up the CPP requirement with the F10 notification requirement. Notifying the HSE (via an F10 form) is only required for projects that exceed certain size thresholds. The CPP, by contrast, is required for every project regardless of size.
The fact that your project is not notifiable does not mean you do not need a CPP. These are two separate requirements under CDM 2015. Many builders assume that because their domestic extension is too small to trigger F10 notification, they do not need any CDM paperwork at all. That assumption is wrong, and it leaves you exposed if the HSE comes knocking.
The CPP must be prepared before the construction phase begins. You should write it during the planning stage, after you have won the job but before your team arrives on site. Writing it retrospectively — after work has already started — is a breach of the regulations.
F10 notification is required under Regulation 6 of CDM 2015 when a project meets either of two thresholds:
Let’s put that in context for a typical domestic extension. A rear kitchen extension with a team of 3–4 workers might take 8–12 weeks to complete. That is more than 30 working days, but you are nowhere near 20 workers on site simultaneously. And 4 workers over 12 weeks is roughly 240 person-days — well below 500.
Most domestic extensions will not trigger F10 notification. But remember: even if F10 is not required, the CPP still is. The HSE’s guidance on CDM 2015 makes this distinction clear. If your project does meet the F10 thresholds, you must notify the HSE before the construction phase begins. You can do this online through the HSE’s F10 notification form.
CDM 2015 does not prescribe a rigid format, but it sets out what the CPP must include. For a domestic extension, the content should be proportionate to the project. You do not need a 30-page document for a kitchen extension — but you do need to cover the essentials.
The site address, a brief description of the work (e.g. single-storey rear extension with new kitchen), expected start and end dates, and working hours. Include the name of the client (the homeowner), your company name, and the names of any other contractors involved.
Who is responsible for health and safety on site? On a domestic extension where you are the only contractor, this is straightforward — you are responsible for everything. State this clearly. If you have subcontractors (electrician, plumber, roofer), explain how you will coordinate their work and communicate site rules.
Identify the main hazards on the project. For a typical extension, this might include working at height (scaffolding, roof work), excavations (foundations), manual handling (blocks, lintels), dust and silica (cutting blocks and concrete), electrical safety (temporary supplies), and working near existing services. Describe the control measures for each.
Set out the basic rules everyone on site must follow. This includes PPE requirements (hard hat, boots, hi-vis, eye protection), working hours, site access and parking arrangements, smoking and eating areas, and rules about visitors and the homeowner’s access to their property during the works.
Describe what welfare provisions are in place. On a domestic extension, this often means using the homeowner’s toilet, washing facilities, and kitchen by agreement. If the homeowner’s facilities are unavailable — for example, if the kitchen is being demolished — you need to arrange alternatives such as a portaloo and hand-washing station.
What happens if there is an accident or emergency? Record the site address (so it can be given to 999), the location of the nearest A&E, the name and contact details of the appointed first-aider, and where the first-aid kit is kept. Include fire precautions if hot works are involved.
Let’s walk through what a CPP might look like for a common domestic project: a single-storey rear kitchen extension measuring 4m x 6m, with strip foundations, blockwork walls, a flat roof, bi-fold doors, and a full kitchen fit-out.
Project details: Mr and Mrs Smith, 14 Oak Lane, Bristol BS7 8QT. Work duration: 10 weeks. Working hours: Monday to Friday, 08:00–17:00, Saturday 08:00–13:00. Principal contractor: ABC Building Ltd. Subcontractors: an electrician and a plumber (arriving weeks 6–8).
Key risks: Foundation excavation (1.2m deep trench — risk of collapse, falling in, underground services). Working at height during roof construction (scaffolding required, edge protection). Manual handling of dense concrete blocks and steel lintels. Dust from cutting blocks and concrete with a disc cutter. Existing gas main runs along the side of the property — hand dig within 500mm.
Welfare: Homeowners have agreed to provide access to their downstairs toilet and kitchen for tea breaks. A hand-washing station will be set up in the garden for use during groundworks. Drinking water available from an outside tap.
Emergency: First-aider is the site foreman (valid first-aid certificate). First-aid kit kept in the site van. Nearest A&E: Bristol Royal Infirmary, 3.2 miles. Site address given to all workers for emergency calls.
This entire CPP fits on two sides of A4. It is specific to the project, covers the real risks, and demonstrates that the builder has thought about safety before starting work. That is exactly what the HSE expects.
Strictly speaking, a CPP is a legal requirement for every construction project. In practice, however, there are situations where the boundary between “legally required” and “good practice” gets blurry.
Consider a joiner fitting a new front door. That is construction work under CDM 2015, so technically a CPP is required. In reality, no HSE inspector is going to ask a joiner for a Construction Phase Plan for a door replacement. The regulations require plans to be “proportionate” — and for very low-risk work, a proportionate plan might simply be the risk assessment and method statement you already have.
For domestic extensions, though, there is no grey area. You are digging foundations, working at height, coordinating subcontractors, and managing a live site for several weeks. The risks are real, the project has complexity, and a CPP is clearly necessary — both legally and practically.
Even where the legal requirement feels disproportionate, having a basic CPP is good practice for several reasons: it forces you to think through the risks before starting, it gives you something to show subcontractors during their induction, and it protects you if there is an incident. If someone is injured on your site and the HSE investigates, being able to produce a site-specific CPP demonstrates that you took your safety responsibilities seriously.
We see the same mistakes come up again and again come up again and again. Here are the most common ones to avoid:
If you are starting from scratch with a blank Word document, a domestic extension CPP will probably take you 1–2 hours. That includes thinking through the risks, writing up the welfare arrangements, and making sure you have covered all the required sections. Most of the time is spent staring at a blank page wondering where to start.
If you are using a good template, you can cut that down to 30–45 minutes. A template gives you the structure and prompts, so you just need to fill in the site-specific details.
With The Site Book’s Lightweight CPP wizard, you can produce a compliant domestic CPP in under 5 minutes. Answer 4 questions about your project, and it creates a professional, site-specific plan that covers all the CDM 2015 requirements. You review it, tweak anything that needs changing, and download a branded PDF. It is the fastest way to tick the compliance box without cutting corners.
Many domestic extensions involve more than one contractor. You might be the main builder handling the structure, but you bring in an electrician, a plumber, and perhaps a roofer as subcontractors. Under CDM 2015, if there are (or will be) more than one contractor on the project, a principal contractor must be appointed.
On a domestic project, because the client duties transfer to the contractor, the role of principal contractor typically falls to the main builder by default. You do not need a formal written appointment from the homeowner — the duty transfers automatically under Regulation 7.
As principal contractor, your responsibilities include: producing and maintaining the CPP, coordinating the work of all contractors on site, making sure everyone receives a site induction, ensuring welfare facilities are adequate, and consulting with workers on health and safety matters. You also need to ensure that only authorised people are allowed on site.
In practice, this means you need to brief your subcontractors when they arrive on site. Show them the CPP, explain the site rules, point out the hazards, and make sure they know where the welfare facilities and first-aid kit are. Record that you have done this. A signed site induction form is the simplest way to demonstrate compliance.
Common questions about CPPs for domestic extensions.
Yes. CDM 2015 applies to all construction work in Great Britain, regardless of size. A single-storey rear extension is construction work, so a Construction Phase Plan is legally required before work starts on site. The plan does not need to be a lengthy document — for a straightforward domestic extension, a proportionate 1–2 page CPP covering the key risks, welfare arrangements, and management structure is perfectly acceptable.
No. Under CDM 2015, homeowners are classified as domestic clients. Their formal CDM client duties — including the requirement to ensure a CPP is produced — transfer automatically to the contractor (or principal contractor if more than one contractor is involved). The homeowner does not need to write or commission the CPP. That responsibility falls to you as the builder.
Starting construction work without a suitable and sufficient Construction Phase Plan is a breach of Regulation 12 of CDM 2015. The HSE can issue improvement notices, prohibition notices that stop work on site, or prosecute. Fines can be significant and a prosecution stays on your record. Beyond the legal risk, not having a CPP means you have not properly considered the hazards on site, which increases the chance of an accident.
Only if the project meets either of the F10 notification thresholds: the construction phase will last longer than 30 working days and have more than 20 workers on site at any one time, or the project will exceed 500 person-days of construction work. Most domestic extensions fall well below these thresholds, so F10 notification is not usually required. However, you still need a CPP regardless of whether the project is notifiable.
Not without tailoring it. The CPP must be ‘suitable and sufficient’ for the specific project, which means it needs to address the actual risks and conditions on that particular site. A generic template used as a starting point is fine, but you must update it to reflect the site address, specific hazards, access constraints, welfare arrangements, and any other site-specific factors. An untailored template will not satisfy the HSE if they inspect.
No. A Construction Phase Plan, a risk assessment, and a method statement are three different documents. The CPP is the overarching plan for how health and safety will be managed across the whole project. Risk assessments identify specific hazards and evaluate the level of risk. Method statements describe the step-by-step procedure for carrying out particular tasks safely. Your CPP should reference your risk assessments and method statements, but it is a separate document that sits above them.
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