RAMS & CPP for House Extensions
What compliance documents you need for rear, side, single and double storey extensions — and how The Site Book handles it for you.
What compliance do you need?
House extensions are one of the most common construction projects in the UK. Whether it's a single storey rear extension or a large double storey wrap-around, CDM 2015 applies — and that means proper planning and documentation.
Do you need a CPP?
Yes. CDM 2015 requires a Construction Phase Plan for every construction project. For extensions, your CPP should cover how you'll manage foundation excavation safely, coordinate multiple trades, and protect both workers and occupants if the property is lived in during the build.
Do you need RAMS?
RAMS are strongly recommended for extension work. The range of hazards — from excavation and structural work through to working at height — means you need to think carefully about risk. Most main contractors and many building inspectors will expect to see RAMS on site.
Common hazards
- Working at height — scaffolding, roof ties, upper floor work
- Excavation collapse during foundation digging
- Structural instability when opening up existing walls
- Underground services (gas, electric, water, drainage)
- Manual handling of blocks, lintels, steels, and roof trusses
- Asbestos in older properties being extended
- Dust and noise affecting occupants in lived-in properties
- Weather exposure during open-roof stages
- Proximity to live overhead or underground services
- Trip hazards and falls in partially completed structures
How The Site Book handles it
Describe your project — "double storey side extension, 1930s semi" — and The Site Book creates your RAMS and CPP automatically. It identifies hazards relevant to your extension type, including structural opening-up, excavation, and coordination of multiple trades.
Ground floor vs two-storey: different risk profiles
The risk profile of an extension changes significantly with height. A single storey rear extension involves foundation excavation, structural openings into the existing building, and roof construction — but working at height is relatively limited. A two-storey extension adds significant scaffolding requirements, heavier structural steel (typically larger RSJs and potentially steel frames), deeper and wider foundations, and sustained working at height across multiple phases. Your RAMS and CPP need to reflect the actual scope. A two-storey extension CPP should detail the scaffolding specification, edge protection arrangements, steel erection methodology, and the sequence of work to ensure structural stability at each stage.
Groundworks and foundations
Foundation excavation is one of the most hazardous activities on an extension project. Trench collapse can be fatal. Your RAMS should address the depth and type of foundations (strip, trench fill, or piled), how excavations will be supported or battered back, how services (gas, electric, water, drainage) will be identified and protected, and how materials will be handled safely. On clay soils, foundations can be deep — sometimes over a metre — and any excavation over 1.2 metres should have properly designed support.
Structural steel and scaffolding
Most extensions require some structural steel, whether it's an RSJ over a new opening or a steel frame for a two-storey build. Steel erection carries specific risks: heavy loads, working at height, temporary instability before the structure is fully connected. Your RAMS should cover the lifting plan, temporary propping, and the competence of the workers doing the installation. Scaffolding must be designed, erected, and inspected by competent persons. If it's in place for more than 7 days, it must be inspected at least every 7 days, and a record kept.
Coordinating multiple trades
Even a modest extension involves multiple trades — groundworkers, bricklayers, carpenters, roofers, electricians, plumbers, plasterers, and decorators. The CPP should set out the sequence of work and how trades will be coordinated to prevent dangerous overlaps. For example, no one should be working below while materials are being lifted to first-floor level. Scaffolding needs to be in place before any work at height. Electrical first fix must be complete and tested before plastering. These sequencing decisions are part of your CPP and are exactly the kind of practical planning that shows an inspector you've thought the job through.
Scaffolding requirements
Scaffolding is required on most extensions above single storey, and often on single storey extensions too — for example, when tying new walls into the existing building at height, or when constructing the roof. Under the Work at Height Regulations 2005, scaffolding must be designed, erected, altered, and dismantled by competent persons. The scaffold must be inspected before first use, after any alteration, after any event that could affect stability (such as high winds), and at intervals not exceeding 7 days. Each inspection must be recorded, and the records kept on site.
For extensions, common scaffolding requirements include: independent scaffold around the perimeter for bricklaying and roof work, a loading bay for materials, ladder access at designated points (not just anywhere on the scaffold), and toe boards and guard rails at every working platform. On a two-storey extension, you may also need an internal scaffold or tower for working at the upper floor level before the permanent staircase is in. If the scaffold is on a public footpath or road, you'll need a licence from the local authority. Your RAMS should specify the scaffold specification, who is responsible for erection and inspection, and the arrangements for access and loading.
Excavation safety for extension foundations
Excavation collapse is one of the most serious risks on an extension project, and one of the most underestimated. A cubic metre of soil weighs roughly 1.5 tonnes — enough to kill. Any excavation over 1.2 metres deep should have properly designed support (trench sheets, hydraulic shoring, or battered-back sides). Even shallower trenches can be dangerous in loose or waterlogged ground.
Before digging, you must identify underground services — gas, electric, water, telecoms, drainage. Use a cable avoidance tool (CAT scanner) and refer to utility plans. HSG47 (Avoiding danger from underground services) is the key HSE guidance. Concrete pours for foundations bring additional risks: manual handling of heavy materials, chemical burns from wet concrete (cement is highly alkaline — pH 12–13), and the logistics of getting ready-mix lorries close enough to pour without destabilising the excavation edges. Your RAMS should cover the excavation method, support arrangements, service identification procedures, concrete pour methodology, and emergency procedures in case of trench collapse.
Working in occupied properties
Many extensions are built while the homeowner is living in the property. This creates additional hazards and management challenges that your CPP needs to address. Dust and noise control become critical — you may need to erect temporary dust barriers between the building works and the occupied areas, use dust extraction on power tools, and agree working hours with the homeowner. Children and pets on site are a real risk that generic RAMS rarely cover — you need clear rules about when the construction area is off-limits and how it will be secured at the end of each day.
Welfare facilities on domestic jobs are typically the homeowner's — toilet, washing, somewhere for tea breaks — but this needs to be agreed in writing and documented in the CPP. If the existing kitchen is being affected by the works, alternative arrangements for hot drinks and food may be needed. Access routes through the property need to be kept clear and safe, with particular attention to temporary steps, changes in level, and the interface between the new build and the existing house.
Coordinating with building control
Building control inspections are a fact of life on extension projects, and your CPP should anticipate them. Key inspection stages include: foundation excavation (before concrete is poured), damp proof course level, oversite preparation, structural steelwork (before it's covered up), drainage connections, first fix electrics and plumbing, insulation, and completion. These inspections require access to the relevant parts of the structure at the right time — which means coordinating your build programme so that work doesn't cover up anything that needs to be inspected.
Your CPP should include the building control notification schedule as part of the project programme. Building control officers visiting site also need to be considered in your site safety arrangements — they need to be briefed on any active hazards and provided with appropriate PPE if required.
Frequently asked questions
- Do I need RAMS for a house extension?
- RAMS are strongly recommended for house extensions, especially where there is structural work, working at height, excavation for foundations, or work near existing services. Most principal contractors and many domestic clients will expect RAMS before work begins.
- What CDM duties apply to a domestic extension?
- Under CDM 2015, domestic clients automatically pass their duties to the contractor (or principal contractor if there are multiple contractors). This means you must plan, manage, and monitor the work to ensure it is carried out safely. A Construction Phase Plan is required regardless of project size.
- Is a double storey extension notifiable to the HSE?
- A project is notifiable to the HSE if it will last longer than 30 working days and have more than 20 workers on site at any one time, or exceed 500 person-days. Most domestic double storey extensions won't meet these thresholds, but larger projects might. When in doubt, check with your principal designer.
- What hazards are common on extension projects?
- Common hazards include working at height (scaffolding, roof work), excavation collapse during foundations, structural instability during opening-up works, underground services (gas, electric, water), manual handling of heavy materials, dust and noise, and asbestos in older properties being extended.
- What's the difference in risk between a single and double storey extension?
- Double storey extensions involve significantly more working at height, heavier structural steel, deeper foundations, and more complex scaffolding. The CPP and RAMS need to reflect these additional risks. Single storey extensions still have significant hazards — structural openings, excavation, services — but the working at height element is typically less.
- How do I coordinate multiple trades on an extension?
- Most extensions involve groundworkers, bricklayers, roofers, electricians, plumbers, and plasterers at various stages. The CPP should set out who is on site when, how handovers between trades are managed, and how you'll prevent clashes — for example, ensuring scaffolding is in place before roof work starts, and that electrical first fix is complete before plastering begins.
- When does an extension become notifiable?
- An extension becomes notifiable when it exceeds either CDM threshold: more than 30 working days with 20+ workers, or 500+ person-days. Most domestic extensions with 3-5 workers over 8-12 weeks come to 120-300 person-days — not notifiable. But a large wrap-around with a complex build programme might cross the line. Calculate it: workers × working days.
- What about extensions on older properties?
- Properties built before the 1990s may contain asbestos in multiple locations — roofing materials, soffits, external cladding, floor tiles, and textured coatings. An asbestos survey should be considered before any demolition or structural work. Lead paint is another consideration on properties built before 1980.
- Do I need separate RAMS for each trade on an extension?
- Ideally, yes. Each trade has its own specific hazards — a groundworker's risks are very different from a roofer's or an electrician's. If you're the principal contractor, each subcontractor should provide their own RAMS for their scope of work, and you should review these to ensure they're adequate and don't conflict with other work on site. If you're doing all the work yourself, you can cover multiple activities in one set of RAMS, but make sure each significant hazard is properly addressed.
- What insurance do I need for an extension project?
- At minimum, you need employer's liability insurance (legally required if you have employees) and public liability insurance. Professional indemnity insurance is also recommended. Your insurance should cover the specific risks of the project — check that your policy covers structural work, working at height, and any specialist activities like asbestos removal. Many clients and building control bodies will ask to see evidence of insurance before work starts. Your CPP should record the insurance arrangements.
- How do I handle an extension on a sloping site?
- Sloping sites add complexity to foundation design and excavation. You may need stepped foundations, retaining walls, or deeper excavations on the downhill side. The risk of excavation collapse is higher on slopes because the soil is already under lateral pressure. Surface water drainage also needs careful planning — water running downhill into open excavations is a common problem. Your RAMS should address the specific ground conditions, the foundation design, and any temporary works needed to manage the slope during construction.
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