- Recognise the commercial cost of over-engineered designs and push back at design stage
- Identify the implied term of reasonable skill and care under SGSA 1982
- Distinguish a TG20:21-compliant from a bespoke designed scaffold
- Apply the CDM 2015 designer competency test
- Identify the four buildability challenges that affect erection efficiency
- Apply the ERIC design risk hierarchy under CDM 2015 reg.9
- Run a design submittal cycle and manage the commercial risk of rejection
- Compose a complete RAMS package referencing SG4, TG20:21 and TG21
- Understand PI and CAR insurance and the BSA 2022 long-tail liability
1. Why Design Matters Commercially
Design is one of the easiest ways to lose money on a job. The work itself may be small but the consequences of a bad design are large. Third-party injury, property damage, prosecution, claim against your PI. Not to mention the costs of over-engineering, with over-use of equipment, reduced productivity on complex builds, additional transport costs and so on.
Most scaffolders don't think of themselves as designers. But every time a scaffolder or supervisor decides where a tie goes, how the scaffold is modified for the site condition, what tube spacing to use, or whether to add a third lift, a design decision is being made. The law treats it as such. This may or may not have a contractual impact depending on the nature of the scaffold purpose or use.
- Competent scaffold designers are formally trained over years, not weeks. BS 5975:2024 defines the competence standard as a combination of HNC-level engineering knowledge, several years of supervised experience and continuing professional development. The result is a small pool of competent designers, and design fees and turnaround times that reflect the scarcity. (BS 5975:2024; ICE Training, Temporary Works Design (Above Ground))
Quick definitions, technical and contractual terms in this module
- RAMS: Risk Assessment and Method Statement. The two documents that together explain what hazards are present (RA) and how the work will be done safely (MS). Required by the Management of H&S at Work Regulations 1999 and CDM 2015.
- Silent contract: a contract that does not expressly cover a specific issue (e.g. design responsibility, defect correction, payment notices). When a contract is silent, the law fills the gap with implied terms. Silence is rarely your friend; the implied term may not be what you want.
- ITP: Inspection and Test Plan. The document that says what gets inspected, when, by whom, and what records are kept.
- QA framework: Quality Assurance framework. The system of processes and checks that proves work meets the specification.
- PIQ: Pre-Information Questionnaire. The temporary works equivalent of pre-tender information. Captures load requirements, ground conditions, tying restrictions, hazards, programme.
- PI insurance: Professional Indemnity insurance. Covers design liability. Most policies are claims-made, meaning the policy in force when the claim is made responds, not when the design was done. Keep run-off cover after a contract closes.
- ERIC: the standard CDM design risk hierarchy: Eliminate the hazard, Reduce the hazard if elimination isn't possible, Inform others of residual risk, Control through procedures and PPE. Used by competent designers under CDM 2015 reg.9.
2. The Commercial Cost of Over-Engineering
A scaffold that's been over-designed costs you money in five ways: more equipment on hire, more labour to erect, slower programme, harder dismantle, and lower kit-fleet turnover. That's less kit to use on more jobs.
Designers who ignore buildability over-specify. Extra ties to be safe. Tighter tube spacing than the loads need. Each one rational on paper. Stacked together they make a scaffold that takes a third more man-hours and a third more kit than a competent design would.
Equipment usage is the hidden cost. Every extra tonne of kit on a job is a tonne not earning hire on another job. Every extra fitting drawn from stock is one not available for the next mobilisation. Fleets are finite. Over-engineering ties up the fleet at the cost of the business.
Programme is the second hidden cost. Complex designs erect slowly. Gangs that should be on lift three are still on lift two. Other trades wait. The MC notices.
Complex designs attract more eyes, more people scrutinising the scaffold, checking and rechecking calculations, requesting revisions, Cat 3 third-party certs. All extends the lead time and can add cost.
Over-engineering is rarely punished by the client and rarely paid for by the designer. It's paid for by the scaffolder, in equipment, hours and goodwill. Push back at design stage. Use designers with clear understanding of buildability.
3. Reasonable Skill and Care, and the TG20 Misconception
Where the supplier carries on a business, there is an implied term that the supplier will carry out the service with reasonable skill and care.
The implied term of reasonable skill and care applies to both the design and the construction of the scaffold.
The implied term applies even when the contract is silent. Silence does not kill design liability.
| Topic | JCT SBCSub/C 2016 | NEC3 ECS | NASC 2018 |
|---|---|---|---|
| Design liability | Subcontractor responsible for design of any portion of the Works it is responsible for designing. Reasonable skill and care implied (Clause 2.13) | Where the Subcontractor designs part of the works, it does so with reasonable skill and care. Design responsibility sits with the Subcontractor (Clause 21.1) | Scaffolding Contractor shall remedy at its own expense any defects drawn to its attention in writing which have arisen from faulty design, erection or dismantling, or the use of defective equipment (Clause 2.6) |
| Implied term of skill and care | Implied by SGSA 1982 s.13 where the contract is silent | Implied by SGSA 1982 s.13 where the contract is silent | Express contractual term at Clause 2.2: Works carried out with due diligence and in a good and workmanlike manner. Design liability at Clause 2.6 runs in parallel |
| TG20 as design defence | TG20 compliance does not remove design responsibility, SGSA implied term remains | TG20 compliance does not remove design responsibility | TG20 compliance does not remove responsibility. Clause 2.6 applies regardless of the design methodology used (NASC CG6:20) |
It is not just an implied term, it is a written contractual obligation. If the scaffold fails because of a design decision made on site, the cost of correction sits with you. The clause requires written notification from the MC, but once notified the obligation to remedy at your own expense is absolute. This applies whether the scaffold was TG20-compliant, bespoke-designed, or modified on the day.
A common misconception in the trade is that a TG20-compliant scaffold isn't "designed". Wrong. TG20 is itself a design standard. Building to TG20:21 doesn't transfer liability away from the contractor.
It is a common misconception that scaffolds designed to BS EN 12811-1 or TG20 relieve the contractor of design liability.
Under the NASC Scaffolding Contract 2018, compliance with NASC Health, Safety and Technical guidance, including TG20:21 and SG4, is a contractual obligation, not a voluntary standard. Clause 2.8 states that the Scaffolding Contractor will comply with all current Health and Safety and Technical guidance issued by NASC. This means TG20:21, SG4, TG21 and all other current guidance are incorporated into the contract by reference. Departing from them without justification is a contract breach as well as a potential statutory breach under WAH 2005.
Under JCT and NEC contracts, NASC guidance must be expressly incorporated via the specification or Works Information to carry contractual weight. On a NASC contract form, it is already there by default.
Any modification to a TG20-compliant scaffold, even small, is a new design event and may attract designer duties under CDM 2015. Scaffolders or supervisors do not have the free reign to modify designed scaffolds because they hold an advanced or inspector's ticket.
4. Designer Competency
A designer must have the skills, knowledge, experience and (if an organisation) the organisational capability to fulfil the duties.
Competency guide: HNC in Civil/Structural/Mechanical Engineering, preferably ICE/IStructE/IET registered; or 5 years' proven scaffolding design office experience; or 5 years in a principal contractor's temporary works department.
Standard prequalification document for designer competency assessment.
5. Scaffolds That Need an Engineer
Some scaffolds always need engineer input. Don't try to TG20 your way around them.
Apply it: TG20-compliant or needs an engineer?
6. Designing for Buildability
Buildability is the gap between what the engineer drew and what the gangs actually have to put up. Most design failures aren't engineering failures. They're failures to think through how a scaffold gets built.
The competent designer doesn't just check the loads. They build the scaffold in their head, lift by lift, and ask: where does the kit come from, how does it get up there, what stays standing while the next bit goes up, where does the gang stand, and how do they reach what they're fixing? Walk a mile in the scaffolder's shoes.
Having experienced and qualified scaffolders and supervisors work with the designers often leads to great on-site results. You get a qualified design, with low kit usage and buildability.
A design that calculates correctly but can't be built efficiently is a bad design.
6.1 Four common buildability challenges
- Material storage and access. Where does the kit live before it goes up? How does it get to the work face? Designs that ignore the loading sequence add days to the build.
- Temporary stability. The scaffold is at its weakest while it's being erected or dismantled. Designs that depend on the final tie pattern for stability are a nightmare to build safely. The right design considers stability at every lift.
- Beams in scaffolding. Prefabricated beams (unit, ladder, aluminium) span gaps but they're heavy, awkward and expensive. Designs that overuse beams when bracing would do are over-engineered. Designs that underuse beams when spans demand them are unsafe.
- Cantilevers and projections. The hardest scaffolds to build. Need careful thought on counterweight, fixing sequence, and how the projection extends without unbalancing the parent scaffold.
6.2 Worked examples, four scaffold types where buildability dominates
- Pavement gantries. Public footpath obstruction with vehicle traffic adjacent. Buildability question: how does the gang erect the gantry without closing the footpath? Common over-engineering: solid foundations specified where pavement bearing capacity would do. Common under-engineering: balk timber fenders forgotten until the licence is checked.
- Temporary bridging for plant. Spans a gap so a tower crane, mobile, or telehandler can cross. Buildability question: what's the loading sequence, will the bridging take the dynamic load of plant in motion, and how does it come out? Common failure: bridging designed for static load, then plant arrives with a different axle pattern from the one assumed.
- Back propping. Supports floor slabs above while the formwork below cures. Buildability question: how do the props transfer load through multiple floors without overloading lower slabs? Common failure: prop heads sit on floor finishes that can't take the point load.
- Hoist run-off. Where a scaffold-mounted hoist meets the working platform. Buildability question: how does the run-off carry the operative weight, the loaded barrow, and the dynamic transfer without flexing? Common failure: insufficient stiffening at the run-off cantilever. Gangs end up adding bracing on the day, off-design, off-record.
6.3 Communication discipline
The designer's job is to give the gangs the right info, not all the info. Twenty pages of calculations buried inside a 50-page submittal is the wrong information. The drawings, the tie pattern, the sequence and the residual risks, in a single readable package, are the right information.
7. Calculations, Risk and Design Checks
When a scaffold needs engineer design, calculations follow. The calculations prove the scaffold can take the loads imposed: dead load (the kit itself), live load (operatives, materials, equipment), wind load, snow load, point loads from any items being craned through, dynamic loads from any work activity (impact, vibration).
7.1 ERIC, the design risk hierarchy
ERIC is the standard CDM design risk hierarchy. Designers are required by CDM 2015 reg.9 to identify and manage design risks. The accepted approach, set out in the ICE Design Risk Management guidance, runs in this order.
A competent design eliminates risk first, reduces second, informs third, controls fourth. A design that jumps straight to PPE has skipped the first three steps.
7.2 What gets calculated
- Standard load (compression, buckling)
- Tie pull-out load (the force the tie has to resist)
- Tube and fitting capacity (section properties from BS EN 12811)
- Foundation bearing pressure
- Beam capacity (where prefabricated beams are used)
- Wind load on sheeted or netted scaffolds (Eurocode 1 Part 1-4)
- Snow load on temporary roofs (Eurocode 1 Part 1-3)
- Load Path Analysis: identify the critical members and verify each one against the relevant failure mode
7.3 The risk of getting it wrong
Two layers of risk. The first is physical: scaffold collapse, injury, fatality, prosecution under HSWA 1974 (unlimited fines, imprisonment for individuals). The second is commercial: PI claim, civil damages, reputational damage, insurance premium hikes, potential to bankrupt a small contractor.
A calculation that's wrong by 10% on paper is a scaffold that fails by 100% on site. Get it checked.
7.4 Verification, design checks under BS 5975:2024
Best practice is a third-party design check. The original designer can't check their own work. The check should be by a different competent designer, ideally with their own PI cover.
The Code of Practice for Temporary Works Procedures sets the framework for design checks. Four categories applied by risk.
- Cat 0: simple, low-risk check by the designer themselves. Restricted to standard solutions.
- Cat 1: independent check within the designer's organisation by a competent person not involved in the design.
- Cat 2: independent check by a competent person from a different team or organisation. Required for moderate complexity.
- Cat 3: external independent check by a separate competent organisation. Required for complex, high-risk, or public-impact designs.
Network Rail uses forms F001/F002/F003 for Cat 3 external checks. Some clients (highway authorities, airports, hospitals) require Cat 3 regardless of complexity.
8. Design Submittal Process
Design submittal is the formal route for getting a scaffold design approved before erecting. Most main contractors have their own version of the process; the principles are the same.
8.2 Rejected designs and the commercial risk
A rejected design is a delay. Delay costs you time and money. The longer the cycle, the more standing time on labour booked and equipment loaded.
Two types of rejection: technical (design doesn't meet the requirements) and process (design submitted incomplete, in the wrong format, missing the design risk assessment). Process rejections are the cheap ones to avoid: get your house in order before submitting.
8.3 Managing the commercial risk
- Build review and resubmission time into your programme. Two weeks turnaround minimum
- Agree the cycle at the pre-let meeting (M5). Get reviewer name, format requirements, expected turnaround documented
- Notify the MC immediately when a design comment delays your works. The notice is the basis for any EOT or compensation claim
- Keep a design submittal log: date submitted, date reviewed, comments received, date resubmitted. Records win disputes
If the design is the critical path, a 1-week reviewer delay is a 1-week project delay. The MC needs to know this. Notice in writing the same day.
| Topic | JCT SBCSub/C 2016 | NEC3 ECS | NASC 2018 |
|---|---|---|---|
| EOT for design delay caused by MC | Extension of time where the MC delays the release of design information or fails to comply with obligations (Clause 2.25) | Compensation event where the MC does not reply to a communication from the Subcontractor within the period required (Clause 60.1(6)) | EOT available for reasons beyond the control of the Scaffolding Contractor. MC design review delay qualifies where it prevents commencement or progress. Written notification required (Clause 13.1) |
| Notification requirement | Written notice as soon as practicable, not later than 28 days after the event (Clause 2.27) | Compensation event notified within 7 weeks of becoming aware, miss it and the entitlement is lost (Clause 61.3) | Written notification that the Works have been delayed. No fixed deadline, notify as soon as practicable (Clause 13.1) |
| Cost entitlement | Direct loss and expense claimable under a separate application (Clause 4.19) | Time and cost recovered through the compensation event mechanism, part of the same assessment (Clause 63) | Direct loss and expense included in any Variation valuation arising from the delay. Notify as a Variation if the delay generates additional cost (Clause 7.2) |
8.4 Drawings, revisions and the priced revision
Every drawing carries a revision letter or number. The revision priced at tender is rarely the revision built. Variations, RFIs, design checks and field changes all generate new revisions.
Record the drawing revision priced in your quotation. Any later revision is a potential variation.
8.5 The PIQ in detail
The PIQ captures everything the designer needs: load requirements, ground conditions, tying restrictions, hazards, programme. Without a complete PIQ the design is at risk of error or rework. The PIQ also forms part of the contractual record. If the client provides incomplete information, they can't blame you for a design that reflects what they gave you.
8.6 Ownership and copyright
Copyright in any drawing remains with the originator unless the contract specifies otherwise.
Where ownership passes to the client, the client can pass the design to another contractor, who must comply strictly with the configuration, materials and specifications.
9. Insurance and Long-Tail Design Liability
If you do design, you carry liability for that design long after the job ends. The Building Safety Act 2022 has lengthened that tail considerably. Insurance has to cover the new tail.
9.1 PI and CAR insurance
Where the design is done in-house, you need suitable Professional Indemnity. Where you use third-party designers, ensure they hold PI too.
- Contractors All Risks (CAR), property damage and third-party injury during the works
- Professional Indemnity (PI), design liability, often on a claims-made basis
If you use third-party designers, verify their PI cover. Without it, your own PI may not respond to a design claim.
| Topic | JCT SBCSub/C 2016 | NEC3 ECS | NASC 2018 |
|---|---|---|---|
| Effect of handover on design liability | Practical Completion does not end design liability. The Rectification Period covers defects but does not cap the design liability tail (Clause 2.30) | Completion does not end design liability. The defects correction period applies to construction defects; design liability runs separately under SGSA s.13 | Issue of a Hand Over Certificate shall not relieve the Scaffolding Contractor of any responsibility with regard to design (Clause 5.3) |
| Long-tail design liability | 6 years from breach for simple contract; 12 years for deed. BSA 2022 extends DPA 1972 claims to 30 years past, 15 years new | Same limitation periods apply | Same limitation periods apply. Clause 5.3 expressly preserves design liability post-handover |
| PI cover implication | Claims-made PI must be in force when the claim is made, not when the design was done. Run-off cover required | Same | Same. Clause 5.3 makes clear the liability continues. PI must cover the full tail |
9.2 The Building Safety Act 2022 long tail
Limitation periods under the Defective Premises Act 1972 extended to 30 years for past work and 15 years for new work. Section 38 of the Building Act 1984 limitation extended to 15 years.
- Past work: 30 years
- New work: 15 years
- Keep PI cover active
- Keep run-off cover after every contract closes
If you undertake design, treat 15-year claims-made PI cover as a minimum and review run-off at the end of every contract. Cheap PI is no PI.
10. RAMS in Depth
RAMS is your single most important contractual safety document. Every scaffolding job needs them. They prove you've thought about the hazards, identified the controls, and trained the operatives.
10.1 What goes into RAMS
- Scope: what work, where, when, by whom
- Hazards identified: falls, falling objects, electrical, structural, public, environmental
- Risk assessment: likelihood × severity, control measures
- Method statement: sequence of operations step by step
- Reference to design: drawing numbers, calculation reference, tie pattern
- Reference to standards: TG20:21 compliance sheet number, SG4 fall prevention measures, manufacturer's handbook for system scaffolds
- Training and competency required: CISRS grade, harness training, manual handling
- PPE schedule: harnesses, helmets, gloves, hi-vis
- Emergency procedures: rescue plan from height, first aid, accident response
- Review and revision history with version numbers
10.2 NASC guidance on RAMS
Preventing Falls in Scaffolding Operations. The single most important reference for the method statement section. Sets the safe system of work for erection, alteration and dismantling.
Compliance sheets reference where the scaffold is a basic configuration. The compliance sheet number goes in the RAMS.
A Guide to Commissioning Scaffold Design. Sets out what should be in a design brief and how to assess a designer's submission.
A RAMS that hasn't been reviewed by a competent person within 12 months is stale. Schedule annual review and update.
11. Inspections, the 7-Day Rule
Statutory inspections by a competent person before first use, after substantial alteration, after exceptional weather, and at intervals not exceeding 7 days.
Action Checklist
- Push back on over-engineered designs at submittal stage
- Verify designer competency before instructing any third-party design
- Verify third-party designer PI cover and your own PI cover before commencing
- Build review and resubmission time into the programme at pre-let stage
- Notify the MC in writing the same day a design comment delays your works
- Record the drawing revision priced and track every later revision
- Schedule annual RAMS review by a competent person
Case Study: The Temporary Roof Collapse
Nine decisions, one per learning objective in this module. This case starts at design brief and walks through to a near-miss on site. Each decision tests one of the principles taught in this module.
Downloads
Templates and trackers for technical documentation and design coordination. Coming soon.
Module 4 Quiz
10 questions. Pass mark is 80% (8 out of 10 correct).
Complete.
You can now push back on over-engineered designs, identify the SGSA s.13 implied term, distinguish TG20 from bespoke, apply the CDM 2015 designer competency test, work the ERIC hierarchy, run a clean design submittal cycle, build SG4-referenced RAMS, and hold the right PI cover for the BSA 2022 long tail. Module 5 picks up programmes and logistics.
- Module 5: Programmes and Logistics
- Module 6: HSE and Legal
- Module 7: Project Controls
References
Harvard-style referencing applies throughout the course.
NASC Commercial Guidance
- NASC (2024) CG8:18 Preparation of Quotations. London: National Access and Scaffolding Confederation.
- NASC (2022) CG11:17 Preparation of Schedule of Rates. London: National Access and Scaffolding Confederation.
- NASC (2019) CG12:19 Contract Clauses. London: National Access and Scaffolding Confederation.
- NASC (2018) CG13:18 Pre-Tender Information from Client. London: National Access and Scaffolding Confederation.
- NASC (2018) CG14:18 Pre-Contract Meetings. London: National Access and Scaffolding Confederation.
- NASC (2021) CG17:09 Commercial Checklist. London: National Access and Scaffolding Confederation.
- NASC (2009) CG18:09 Daywork. London: National Access and Scaffolding Confederation.
- NASC (2018) CG19:18 Liquidated and Ascertained Damages. London: National Access and Scaffolding Confederation.
- NASC (2022) CG7:17 Late Payment of Commercial Debts. London: National Access and Scaffolding Confederation.
Standard Forms of Contract
- Construction Industry Publications Ltd (2018) Scaffolding Contract 2018: Form of Contract for the Erection, Hire and Dismantling of Scaffolding. Birmingham: Construction Industry Publications Ltd.
- Joint Contracts Tribunal (2016) Standard Building Sub-Contract Conditions (SBCSub/C 2016). London: Sweet & Maxwell.
- NEC (2013) NEC3 Engineering and Construction Subcontract (ECS). London: Institution of Civil Engineers.
RICS
- RICS (2nd edn) New Rules of Measurement (NRM2): Detailed Measurement for Building Works. London: Royal Institution of Chartered Surveyors.
- RICS (current edn) Definition of Prime Cost of Daywork carried out under a Building Contract. London: Royal Institution of Chartered Surveyors.
- RICS (Black Book current edn) Cost Reporting and Variations. London: Royal Institution of Chartered Surveyors.
CIOB
- Chartered Institute of Building (current edn) Code of Estimating Practice. 8th edn. Bracknell: CIOB.
- Chartered Institute of Building (2022) Code of Practice for Project Management for the Built Environment. 5th edn. Chichester: Wiley-Blackwell.
Industry Reports and Research
- CMS Cameron McKenna Nabarro Olswang LLP (2024) Late Payment Reform: What UK Construction Developers and Contractors Need to Know. Available at: cms.law.
- Construction Industry Council (2025) The £6 Billion Question: Why is Construction Still Paying Like It's 1999. Available at: cic.org.uk.
- HKA (2024) CRUX Insight Eighth Annual Report: From Insight to Foresight. Available at: hka.com.
- HM Government (2024) Late Payments Consultation: Tackling Poor Payment Practices. London: Department for Business and Trade. Available at: gov.uk.
- Pye Tait Consulting (2017) Retentions in the Construction Industry. BEIS Research Paper No. 17. London: Department for Business, Energy and Industrial Strategy. Available at: gov.uk (PDF).
- World Commerce and Contracting (n.d.) Stopping the Leak: The Value of Contracts. Available at: worldcc.com.
Legislation
- Sale of Goods Act 1979, c. 54. London: HMSO.
- Supply of Goods and Services Act 1982, c. 29. London: HMSO.
- Unfair Contract Terms Act 1977, c. 50. London: HMSO.
- Late Payment of Commercial Debts (Interest) Act 1998, c. 20. London: TSO.
- Late Payment of Commercial Debts Regulations 2002, SI 2002/1674. London: TSO.
- Late Payment of Commercial Debts Regulations 2013, SI 2013/395. London: TSO.
Case Law
- Butler Machine Tool Co Ltd v Ex-Cell-O Corporation (England) Ltd [1979] 1 WLR 401.
- Cavendish Square Holdings BV v Talal El Makdessi [2015] UKSC 67.