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Short answer

When does a scaffold need a design in the UK?

When it is not covered by a recognised standard configuration. In practice, if the NASC TG20:21 or TG30 eGuide cannot produce a compliance sheet for it, or the manufacturer’s instructions do not cover it, the scaffold needs a bespoke design by a competent person.

By Ole Emil Frikstad Urstad · How the numbers are computed ·

SGB CUPLOK scaffolding around a house of 11.4 × 5.3 m with a gabled roof (eaves 4.5 m, ridge 6 m), drawn by the ScaFix 3D model
SGB CUPLOK around the example house, as ScaFix draws it in 3D.

When does a scaffold need a design?

Under Schedule 3, Part 2, paragraph 7 of the Work at Height Regulations 2005, strength and stability calculations are required unless a note of calculations covers the arrangement or it follows a generally recognised standard configuration. For tube and fitting that is a TG20:21 compliance sheet, for system scaffolds TG30 or the manufacturer’s instructions; anything outside needs a bespoke design.

What does paragraph 7 actually say?

Schedule 3, Part 2 of the Work at Height Regulations 2005 sets two duties for every scaffold:

ParagraphDutyWhat satisfies it
7Strength and stability calculations, unless a note of calculations covering the arrangement is available or the scaffold is assembled in conformity with a generally recognised standard configurationA TG20:21 or TG30 compliance sheet, the manufacturer’s instructions, or a bespoke design
8An assembly, use and dismantling plan drawn up by a competent person, which may be a standard plan supplemented with the details of this scaffoldA method statement or plan for this scaffold

The regulations never name TG20. HSE and NASC treat TG20:21 for tube and fitting scaffolds, and NASC’s TG30 for system scaffolds such as cuplock and ringlock, as the recognised standard configurations (HSE scaffolding guidance). TG20:21 is delivered as an Operational Guide, a Design Guide and an eGuide that generates compliance sheets (Construction Management, April 2021).

How do you know if your scaffold is outside the standard?

The NASC FAQ gives the simplest test: if the eGuide cannot produce a compliance sheet, the scaffold needs a bespoke design with input from a competent engineer. HSE lists typical cases that fall outside standard configurations:

  • shoring scaffolds, and cantilevered or truss-out scaffolds;
  • access scaffolds with more than two working lifts in use at once;
  • towers that need guys;
  • slung or suspended scaffolds, and boiler scaffolds;
  • anything modified so that it leaves the standard configuration.

Sheeting, heavy loading bays and hoists usually push a scaffold out as well, because they change the tie forces and the loads on the standards; the effect of sheeting on ties is in scaffold ties and anchoring. The height question is covered in how high can scaffolding be.

Kwikstage scaffolding around a house of 11.4 × 5.3 m with a gabled roof (eaves 4.5 m, ridge 6 m), drawn by the ScaFix 3D model
Kwikstage around the example house, as ScaFix draws it in 3D.

What should the contractor give you?

HSE expects the scaffold contractor to come back with the design basics: scaffold type, bay length, lift height, load class, leg loads and tie spacing. For a standard scaffold that is the compliance sheet; for a designed one, drawings and calculations from the designer. Ask for it at tender, together with the handover certificate described in what a scaffold handover certificate should contain, and keep both with the inspection reports required by regulation 12.

Does a design change who may build it?

Yes. A CISRS Scaffolder card covers basic scaffolds as defined in TG20; complex designed structures belong to an Advanced Scaffolder. The full rule set, from CDM 2015 to CISRS cards and highway licences, is in UK scaffolding regulations and TG20.

ScaFix plans a facade scaffold in 3D with bays, lifts and a parts list for any of its 110 systems, which helps brief a contractor or designer; it does not issue a TG20 compliance sheet or a design.

Planning information, not structural approval. A TG20:21 or TG30 compliance sheet, the manufacturer’s instructions or a bespoke design by a competent person decides what may be built under Schedule 3 of the Work at Height Regulations 2005, and a competent person inspects the scaffold before use.

Frequently asked questions

Is TG20 a legal requirement?

No document named TG20 appears in the regulations, but Schedule 3 accepts a recognised standard configuration instead of calculations, and HSE and NASC treat TG20:21 as that configuration for tube and fitting. Outside it, you need a design.

Does a system scaffold need a TG20 compliance sheet?

No. System scaffolds follow the manufacturer’s instructions or NASC’s TG30; TG20:21 covers tube and fitting scaffolds.

Does a sheeted scaffold need a design?

Often. Sheeting raises the wind load on every tie, so unless the compliance sheet or the manufacturer’s instructions cover that sheeting, a design is needed before it goes on.

Who can design a scaffold?

A competent person, usually a scaffold designer or temporary works engineer. HSE expects the design to state bay length, lift height, load class, leg loads and tie spacing.

Sources

Primary sources used for this article, with the date each was read.