TG20 scaffolding compliance explained for principal contractors

TG20 is the design guide that quietly underpins almost every tube and fitting scaffold erected in the UK. As a principal contractor, project manager, site manager, or quantity surveyor, you do not need to be able to design a scaffold yourself, but you do need to know what TG20 covers, what falls outside it, and what to check on a scaffolder's submission before you let it onto site. This guide explains TG20 in plain English for non-scaffolders, and walks through what to look for in the documents your scaffolding subcontractor sends you.

What TG20 actually is

TG20 stands for "Technical Guidance 20", published by the National Access and Scaffolding Confederation (NASC). It is the industry design guide for tube and fitting scaffolding in the UK. The current version is TG20:21, replacing TG20:13 (which itself replaced earlier editions going back to 1990).

The Work at Height Regulations 2005 require that any scaffold either be assembled to a "generally recognised standard configuration" or be designed by bespoke calculation. TG20 is the document that defines what a "generally recognised standard configuration" looks like for tube and fitting work. If a scaffold falls within TG20 parameters, the compliance sheet IS the design — no further engineering calculation is required. If it falls outside, a bespoke design by a qualified scaffold engineer is mandatory.

This matters for principal contractors because:

You do not need a bespoke design for every scaffold on your project. The TG20 compliance sheet is sufficient for standard configurations and that is what you should expect to receive for most scaffolds.
You DO need a bespoke design for any scaffold outside the TG20 envelope. If your scaffolder hands you a TG20 sheet for a non-standard scaffold, the document is invalid and the scaffold cannot legally be used.
TG20 is updated periodically. TG20:21 superseded TG20:13 in 2021 and changed several aspects of the parameters. Documents based on the older version may not reflect current requirements.

NASC sells TG20 access through an annual subscription (typically £200-£400 per year per company) which provides the digital eGuide and access to the compliance sheet generator. Most scaffolding contractors hold a subscription as a normal cost of doing business.

What TG20 covers

TG20 covers tube and fitting scaffolds within a defined envelope of parameters. The specifics evolved between versions, but for TG20:21 the standard configurations include:

Independent scaffolds (free-standing, tied to the building)
Putlog scaffolds (with one end of the transom built into the brickwork - now rare on modern construction but still common in some refurb work)
Birdcage scaffolds (internal floor-to-ceiling scaffolds for ceiling work)
Mobile and static towers up to certain heights

Each configuration has parameter limits. For independent scaffolds, the typical envelope is:

Maximum height (usually limited by working platform height plus parapet)
Maximum lift heights (the vertical distance between platforms)
Maximum bay lengths (the horizontal distance between standards)
Permissible loadings (light duty / general purpose / heavy duty)
Tie patterns (frequency and arrangement of ties to the building)
Bracing requirements (longitudinal, transverse, plan)
Wind loading (based on UK regional wind speed maps)
Environmental factors (sheeting, netting, debris management)

If all parameters are within the envelope, the TG20 compliance sheet covers the scaffold. The sheet is generated by the scaffolder using NASC's eGuide software, which checks the parameters against the rules and produces a one-page compliance certificate naming the configuration and the design assumptions.

What falls OUTSIDE TG20

This is what principal contractors most commonly miss. The TG20 envelope is narrower than people think. Common scaffolds that fall outside TG20 and require bespoke design include:

Heavy loadings. Scaffolds intended to support significant material storage (bricks stacked on the platform, large quantities of tiles, plant) usually exceed TG20 light/general/heavy-duty limits.
Suspended scaffolds. Hanging scaffolds, swing stages, cradles - all outside TG20.
Cantilevered scaffolds. Scaffolds where the platform projects beyond a support point, common over walkways or pavements.
Temporary roofs. Tied scaffolds with covered roofs (for weatherproofing during refurb work) almost always require bespoke design due to wind uplift loadings.
Scaffolds with debris netting on exposed elevations. Netting changes the wind loading significantly. Many TG20 sheets become invalid the moment netting is added without recalculation.
Mast climbers and powered access integrated with scaffolding. Outside TG20.
Scaffolds supporting tower cranes, hoists, mechanical handling plant. Always bespoke.
Restricted tie locations. If the building structure does not permit standard tie patterns (e.g. heritage buildings, glass facades, listed properties), the scaffold needs bespoke design.
Birdcages over a certain height or with non-standard internal layouts. Smaller birdcages fit TG20; larger ones rarely do.
Anything taller than typical 4-5 storey domestic / small commercial work. The exact height depends on configuration, but most TG20 standard configurations top out at heights that make tall buildings ineligible.
System scaffold. TG20 is for tube and fitting only. System scaffold (Layher, Cuplok, Plettac, Kwikstage, Haki, Peri Up) follows the manufacturer's user guide instead. The principle is the same — pre-calculated standard configurations within an envelope, bespoke design outside it — but the document is different.

If you receive a TG20 compliance sheet for any of the above without a separate bespoke design, raise it with the scaffolder before allowing the scaffold onto site.

What a TG20 compliance sheet looks like

A valid TG20 compliance sheet typically includes:

The project name and site address
The scaffolding company name and contact
The configuration reference (which TG20 standard configuration is being used)
Key parameters: maximum height, lift heights, bay lengths, tie pattern
Loading category (light, general, heavy duty)
Wind loading assumption based on the regional wind map
The eGuide reference number proving it was generated from the official tool
The date of generation and the version of TG20 used (should be TG20:21 in 2026)
The name and signature of the competent person who produced the sheet

If the document does not include the eGuide reference number, treat it with suspicion. Some less reputable scaffolders produce hand-typed "TG20 compliance" documents without using the official tool. These have no validity. The eGuide reference is what proves the sheet came from the official source.

What a bespoke design looks like

For scaffolds outside TG20, the document you should receive is a bespoke scaffold design, typically including:

Calculations showing the scaffold has adequate strength, rigidity and stability
Specific tie locations and design loadings
Specific bay lengths, lift heights, and bracing
Loading capacity and permissible material storage
Wind loading calculations specific to the location and configuration
Drawings showing the scaffold in elevation, plan, and section
An engineer's stamp or sign-off, with their qualifications
A method statement covering erection sequence and stability during construction

Bespoke designs are produced by qualified scaffold designers — typically members of the Institute of Structural Engineers (IStructE) or the Chartered Institution of Civil Engineers (ICE) with scaffolding-specific experience, or specialist scaffold design consultancies.

The cost of a bespoke design depends on complexity. A modestly non-standard scaffold (slightly taller than TG20, additional loading) might cost £200-£600 to design. A complex bespoke (suspended, temporary roof, cantilever) can cost £1,500-£5,000 or more. Designs are project-specific and not transferable.

Inspections after erection

Once the scaffold is erected, the Work at Height Regulations require inspection:

Before first use
After any event likely to have affected stability (high winds, impact, alteration)
At intervals not exceeding seven days

The seven-day interval is hard. A scaffold that has not been inspected within the last seven days is not legally compliant and cannot be used until it is. As a principal contractor, this is one of the simplest things to check on a site walk: when was the last scaffold inspection, where is the record, who signed it.

The inspection must be by a competent person. Competence is normally established through a CISRS Scaffolding Inspection card, but a non-scaffolder with appropriate training (typically a site manager who has completed a 1-2 day basic inspection course) can inspect basic structures. Each inspection must be recorded on a suitable form. Inspection records must be kept for the lifetime of the scaffold plus three months.

The HSE's scaffolding guidance sets out the inspection regime in full.

Handover certificates

The scaffold handover certificate is the document that transfers responsibility for the scaffold from the scaffolding contractor to the principal contractor (or whoever is the user of the scaffold). Without a handover, no other trade should step onto the scaffold.

The handover should record:

Project name and site address
Scaffolding contractor name
Date of handover
Configuration reference (TG20 sheet ID or bespoke design ID)
Permissible loadings (light duty, general purpose, or heavy duty)
Any restrictions or conditions of use
The signature of the scaffolding company's competent person
The signature of the receiving party

If alterations are made — even seemingly minor ones, such as removing a board, repositioning a tie, or adding a brace — a new handover is required. This is a compliance area where small habits cause big problems. A bricklayer who shifts a board to get easier access has, technically, invalidated the handover. Train your trades that any alteration is the scaffolder's job.

What to check before you let a scaffold onto site

As a principal contractor running a project, before you accept a scaffold onto site, you should have on file:

The scaffolding contractor's CHAS, SMAS or Constructionline accreditation, in date
NASC membership certificate if the contract requires it
Public liability and employers' liability certificates, in date, sufficient amount
CISRS card photographs for every operative on the gang, both sides, in date
The TG20 compliance sheet (with eGuide reference) OR the bespoke design (with engineer's stamp)
The project-specific RAMS, signed by the author and the team
Asbestos awareness, manual handling and first aid certificates for the gang
The handover certificate after erection completes, before any other trade uses the scaffold

Not having these in your files at the start of the project is the single most common compliance failure on UK construction sites. An HSE inspector arriving unannounced will ask for them, and "we are getting them" is not an answer.

Common things that go wrong

The TG20 sheet is for the wrong configuration. Scaffolders using a copied template instead of generating a new sheet through the eGuide for this specific project. Spot it by checking the project name on the document and the eGuide reference.

The TG20 sheet covers a scaffold that is actually outside TG20. The most common is netting added to a TG20 elevation without bespoke recalculation. Catching it requires looking at the actual scaffold and comparing to the document.

Inspections lapse beyond seven days. The scaffold continues to be used despite no recent inspection. Spot it by reviewing the inspection log on every site walk.

Alterations made without re-handover. The scaffold has been modified by the scaffolding contractor (e.g. an extension added) but the original handover certificate has not been updated. Check the handover document matches the scaffold actually erected.

Operatives at the gate without valid CISRS cards. Card has expired, or the operative is at a higher grade than their card permits. The pre-start gate check is your defence.

The scaffolding contractor has lost NASC membership. Membership lapsed but the certificate on file is from the previous year. Most main contractor pre-start packs require an annually-refreshed certificate.

The compliance burden on the scaffolding subcontractor

From the scaffolder's side, supplying all of the above to every principal contractor on every project is a substantial administrative effort. Multiple inspections per scaffold per week. RAMS for every project. Handover certificates after erection. CISRS cards refreshed every five years. Insurance, accreditation, NASC, training records all kept current. Documents shared with the principal contractor before each project starts, and re-shared on demand throughout the project.

The scaffolding companies that win the most main contractor work tend to be the ones that have invested in compliance infrastructure rather than the ones that scramble for documents at every project gate. From a principal contractor's perspective, asking for documents and getting a clean, in-date pack within 30 minutes is the strongest signal that the scaffolder takes safety seriously.

Complys is built for UK scaffolders. Every TG20 design, every CISRS card, every RAMS, every inspection record, every accreditation in one place, with one-click sharing to any main contractor and automatic expiry alerts. Start a 90-day free trial if you are running scaffolding work and want to make compliance a competitive advantage rather than a daily fight. Our scaffolding compliance guide covers the wider document set most contracts require, and our principal contractor compliance checklist is what most main contractors use to vet subcontractors at prequalification.

Quick reference for principal contractors

What to check on every scaffold on your project:

TG20 compliance sheet WITH eGuide reference, OR bespoke design WITH engineer's stamp
Configuration matches the actual scaffold erected
All operatives' CISRS cards photographed, in date
RAMS specific to this project, signed and dated
Handover certificate signed off after erection, before any other trade uses
Inspection records dated within the last 7 days
Public liability £10m, employers' liability £10m, both in date
SSIP accreditation in date
NASC membership if the contract requires it

If any of these is missing or out of date, the scaffold is not ready for use. Send the scaffolder back to fix the gap. Document the issue in your project records. The cost of being strict at the start is far smaller than the cost of an HSE prosecution or a serious accident.