TG20 compliance, explained: what a compliance sheet actually tells you

Most disputes about a scaffold start with a simple question that nobody on site can answer quickly: what was this built to? TG20 exists so that question has a short answer for the majority of ordinary scaffolds — a compliance sheet, generated for that structure, saying it matches a configuration that has already been checked.

What TG20 is

TG20 is NASC's technical guidance for tube and fitting scaffolds. The current edition is TG20:21, and it comes with an eGuide — software that takes the details of the scaffold you intend to build and, if that configuration sits inside the guidance, produces a compliance sheet for it. That sheet is the evidence. It names the structure, the configuration, the loading class and the tie pattern it depends on. Recording which sheet a structure was built to is the first thing the platform asks for.

The important word is configuration. TG20 does not bless a scaffold in general terms; it confirms that a specific arrangement — these bay lengths, these lift heights, this tie pattern, this cladding, this duty — has been assessed and can be built without a bespoke design behind it.

What a compliance sheet does not do

• –It does not survive a change. Add a lift, sheet it, hang a loading bay off it or reduce the ties, and the sheet you hold describes something that is no longer standing on site.
• –It does not replace inspection. A compliant design says the scaffold can be built safely; only an inspection says it was, and still is.
• –It does not cover every structure. Anything outside the guidance needs a design from a competent person, not a compliance sheet.
• –It is not a handover certificate. Design and handover answer different questions — what it should be, and what was actually handed over.

Keeping the sheet attached to the scaffold

The practical failure is rarely producing the sheet. It is finding it eighteen months later, for the right structure, in a form that matches what was built. Compliance sheets that live in a folder on one machine drift away from the scaffolds they describe the first time someone adapts a structure without going back to the paperwork.

The fix is boring and effective: hold the design against the structure record rather than against the job, and make an adaptation something you log rather than something you remember. Then the question "what was this built to?" has an answer that includes the date it changed.

Where compliance gets lost between office and site

The common failure is not misunderstanding the guidance. It is that a compliant design leaves the office and something changes on site — ground conditions differ from the survey, a tie cannot go where it was drawn, a client asks for an extra lift — and the structure erected is no longer the structure that was signed off. Nobody set out to depart from it; the site adapted to what it found.

Which is why logging adaptations matters as much as the original design. A departure that is recorded, assessed and signed off is a managed change; the same departure unrecorded is a structure whose compliance basis no longer exists on paper.

Common mistakes

• –Treating the compliant design as the end of the compliance question
• –Site adaptations made sensibly but never recorded or reassessed
• –No route for a chargehand to flag that the structure has departed from the drawing
• –Assuming a structure still falls within the guidance after loading or use changes
• –Relying on the original sign-off for a structure that has since been altered
• –No link between the design, the handover record and what is actually standing

Worth knowing: keep the basis with the structure

The practical weakness in most firms is not understanding compliance but retrieval: being able to say, for a specific structure standing on a specific site today, what its compliance basis actually is and where the document lives. That question arrives from clients, auditors and occasionally investigators, and it arrives without notice.

Holding the basis against the structure in a register — rather than in a job folder organised by contract — is what makes that answerable in minutes. It is the same reason inspections, adaptations and handovers should all reference a structure the same way.

• –Hold the compliance basis against the structure, not just the job
• –Reference structures identically across design, inspection and handover records
• –Make sure site can see which basis applies to what they are standing on
• –Update the basis when the structure is altered, not only when it is designed

Where this connects: the compliant structure and the standing one

Compliance is established at design and tested on site, and the distance between those two moments is where most firms lose it. A structure signed off against the guidance on a Tuesday is being built on a Thursday by people solving problems the drawing did not anticipate, and every one of those solutions moves the structure slightly away from its basis.

That is not an argument for stopping site from adapting — it could not work and would not be safe. It is an argument for the adaptation being the thing that triggers a reassessment, so the compliance basis travels with the structure rather than describing the one that was intended. A firm that can produce, for any standing structure, both its original basis and every change since is compliant in a way a firm holding only the first is not.

• –Hold the compliance basis against the structure, not the contract
• –Make an adaptation the trigger for reassessment, not a site task
• –Reference the structure identically across design, inspection and handover
• –Make the basis reachable by the people standing on the structure
• –Reassess when loading or use changes, not only when geometry does
• –Check the current published guidance rather than an internal summary