NASC takes a closer look at what compliant scaffolding design really involves, from design routes and limits of compliance sheets to client duties, safe buildability and managing changes throughout a project

In the previous edition of Government Business, NASC set out three tests for good scaffolding procurement: credibility, competence and compliance. A credible firm, employing competent staff, working to a compliant design. The first two are straightforward to verify at tender stage. The third is where clients tend to have least confidence, because it involves engineering rather than document checks. 
This is a closer look at what compliant design means in practice.

Every scaffold is designed
There is a widespread assumption that scaffolding design applies only to unusual or complicated structures, and that a straightforward scaffold on a straightforward building does not really need designing. That assumption is wrong and correcting it changes what a client asks for.
Under the Work at Height Regulations 2005, every scaffold must be designed. There are two legitimate routes to satisfying that. The first is erection to a recognised standard configuration, evidenced by compliance sheets produced via NASC’s ePortal which includes TG20 for tube and fitting scaffold and TG30 for system scaffold. System scaffold manufacturer user manuals can also be used to provide these standard configurations. 

The second is a bespoke design produced by a competent scaffold designer, supported by calculations.
There is no third option. If a scaffold on your site has neither a compliance sheet nor a bespoke design behind it, something has been missed.

Understanding the limits of a compliance sheet
Compliance sheets exist because most scaffolds are variations on a small number of well understood forms. NASC’s TG20 and TG30 guidance sets out pre-engineered configurations, designed to BS EN 12811 and recognised by the HSE, covering the majority of everyday scaffolds. A compliance sheet contains everything needed to build the specified structure and can be produced quickly for any job sitting inside the envelope the guidance covers.

The word to focus on here is ‘envelope’. Compliance sheets have limits, and once a scaffold exceeds them, whether through height, loading, bay size, sheeting or the way it must be tied to the building, the compliance sheet no longer applies. A bespoke design with calculations is then required, produced by a competent designer working to the appropriate design standard. NASC publishes guidance on commissioning that work in TG21 A Guide to Commissioning Scaffold Design, and CG6 Scaffolding Design.

The risk for clients is rarely that a contractor ignores this. Reputable contractors do not. The more common problem is a scaffold that starts inside the envelope and drifts outside it, because the programme changed, because another trade needed heavier loading, or because sheeting went on that was not originally specified. The scaffold was compliant when it went up and stopped being compliant when the work changed around it. This highlights the importance of a clear and comprehensive design brief from the outset. The scaffold should be designed not simply for the conditions known at the point of erection, but with its intended use, loading, sequencing and reasonably foreseeable modifications considered throughout its life. 
A clear brief, developed in accordance with the relevant regulations and guidance, and with the principles of BS 5975 applied where appropriate, should establish those requirements from the outset and provide a clear basis for managing changes as the project develops. 

NASC guidance is clear that a system for managing design variations should be in place. For a client, this is a more revealing question at tender stage than most of the standard ones. Ask how a contractor handles a change of use mid contract, and the answer tells you a good deal about how they work. 

What a design should contain
Where design drawings are produced, they should show an elevation of the scaffold with every tie position marked, stating the tie classification: light duty at 3.5kN, standard at 6.1kN, or heavy duty at 12.2kN.
Ties deserve attention because they are the point at which the scaffold depends on your structure rather than on itself. Anchors installed into concrete or masonry must be tested in accordance with NASC TG4, five percent of the total number of ties and a minimum of three, whichever is greater, and proof loaded to 1.25 times the required tensile load. Records must be kept and copies issued to you as the client.

Design carries CDM duties
Scaffold designers hold duties under the Construction (Design and Management) Regulations 2015 like any other designer. NASC guidance is explicit that designers must consider and evaluate the risks involved in erecting and dismantling their proposals, and design to eliminate or reduce risk and ensure safe buildability as part of the brief.

That phrase, safe buildability, is worth holding onto. A scaffold can be perfectly sound once complete and still be difficult or hazardous to build. A design that has not considered the erection and dismantling sequence pushes that problem onto the scaffolders. Clients rarely see this, but it is one of the clearest markers of a design done properly rather than produced to satisfy a documentation requirement.

What the client has to provide
Design compliance is not something a client can procure and then step away from. The information a contractor receives at tender and design stage determines the quality of what comes back.

That includes what the scaffold is for and which trades will use it, the loads it will carry, how long it will be in place, whether it needs sheeting or netting, and what access is required. On access, NASC guidance SG25 sets out a hierarchy putting permanent staircases and hoists first and ladder access considerably lower. It is the client or principal contractor, not the scaffolding contractor, who is responsible for assessing what a project needs and recording it in the client brief. A scaffold serving an occupied residential block calls for a different access solution from one serving a short roof repair, and that judgement belongs to the client.
Public sector projects also carry considerations a contractor cannot anticipate without being told. Occupied buildings, public footfall, school terms, ward access and evacuation routes all shape what a compliant design looks like. Providing that information early is a condition of getting a design that works.

What the client should receive, and what happens next
When a scaffold is completed, it should be inspected in accordance with the Work at Height Regulations 2005 and formally handed over with the paperwork that goes with it: report of inspection, design drawings and calculations, or the relevant compliance sheet, together with tie testing records. NASC guidance SG35 covers handover, and until it takes place the scaffold should display a ‘do not use’ notice.

One point here is regularly missed by clients and carries real consequences. Once a scaffold has been handed over, responsibility for the statutory inspection every seven days sits with the hirer or user, not the scaffolding contractor. Organisations that assume this is covered by the contract can find themselves months into a project with an uninspected scaffold and no record to show. If you have no competent inspector in house, you can instruct the contractor to carry out the duty on your behalf, but that must be a separate instruction rather than an assumption.

Mark Collinson, head of technical at NASC, said: “Compliance in scaffolding design is not about generating paperwork. Every one of these requirements exists because something went wrong at some point and the industry learned from it. For clients the practical test is simple. Ask to see the compliance sheet or the design before the scaffold goes up and ask what happens if the job changes. A good contractor will have the answer ready, because they will have asked themselves the same question already.”

Checking design compliance is not complicated. It means knowing that every scaffold must be designed, knowing which of the two routes applies, ensuring there is a clear and suitably detailed design brief, and asking to see the evidence before work starts. Just as importantly, it means understanding how the scaffold is intended to be used, how changes and modifications will be managed throughout its life, and what your own duties are once the scaffold is handed over. 

Clients who ask those questions consistently tend to get better scaffolds, from contractors who were going to do it properly anyway.