TG20:21 Scaffolding Standard Explained
The TG20-21 scaffolding standard explained for homeowners: what a compliance sheet is, when a scaffold design standard UK job needs an engineer instead.
The tg20-21 scaffolding standard is the technical guidance that governs how most UK tube and fitting scaffolds are designed. If your scaffolder mentions a compliance sheet, this is what they are referring to.
You do not need to understand the engineering. You do need to know which of two routes your scaffold sits on, because it tells you whether the structure has a proper design basis.
What TG20:21 is
TG20 is published by the National Access and Scaffolding Confederation, the industry body for UK scaffolding. The current edition is TG20:21, which replaced TG20:13.
It sets out pre-calculated standard configurations for tube and fitting scaffolds, covering the large majority of independent and putlog scaffolds used in the UK. Rather than every scaffold needing bespoke calculations, a scaffolder can select a configuration that has already been engineered and confirm their structure matches it.
Following TG20:21 supports compliance with the Work at Height Regulations 2005, which is the actual law. TG20 is guidance rather than legislation, but it is the recognised route to demonstrating a scaffold is adequately designed.
The compliance sheet
The practical output is a TG20 compliance sheet, produced from the NASC eGuide software. It is a PDF, typically one or two pages, and it states:
- the scaffold configuration it covers
- the maximum height and bay length
- the duty rating, meaning what loads the scaffold may carry
- the tie pattern and frequency required
- bracing requirements
- ledger and transom spacing
- an illustration of the compliant arrangement
Ask for it. On a standard domestic scaffold, a firm that can produce a compliance sheet is demonstrating that the structure was selected rather than improvised.
The two routes
Every tube and fitting scaffold sits on one of two routes.
| Route | When it applies | What you get |
|---|---|---|
| TG20 compliant | Standard configuration within the published limits | Compliance sheet from the eGuide |
| Bespoke design | Anything outside those limits | Calculations from a qualified engineer, £150 to £400 |
Things that commonly push a scaffold onto the bespoke route:
- Sheeting or netting, which substantially increases wind loading
- Bridging over a conservatory, porch or entrance
- Cantilevered sections
- Unusual height relative to the base width
- Restricted or unusual tie points, common on listed and period property
- Loading bays and heavy material storage
- Temporary roofs
- Ground that cannot take standard base loading
Neither route is better. What matters is that the scaffold has a design basis appropriate to its type, and that the scaffolder can tell you which one applies.
Duty ratings
TG20 sets load classes, and this is the part that catches homeowners out. A scaffold rated for inspection and light work is not rated for a pallet of tiles.
| Duty | Typical use |
|---|---|
| Light duty | Inspection, painting |
| General purpose | Most domestic work, roofing, gutter replacement |
| Heavy duty | Masonry, block laying, material storage |
If a trade intends to load materials onto the scaffold, the scaffolder needs to know before they build it. Retrofitting a heavier duty rating means altering the structure.
System scaffold is different
TG20:21 covers tube and fitting only. System scaffolds such as Layher and Cuplock are erected to their manufacturer’s own design guidance and load tables instead.
Both are legitimate. The comparison is in System Scaffold Cost and Tube and Fitting Scaffold Cost.
What to ask
Three questions, all reasonable and all quick to answer:
- Is this scaffold TG20 compliant, or does it need a bespoke design?
- Can I see the compliance sheet or the design once it is up?
- What duty rating is it, and does that cover materials being stored on it?
A competent firm answers all three without hesitation. Vagueness on a complex elevation, particularly one being sheeted or bridged, is worth a second opinion.
What changed from TG20:13
TG20:21 replaced the 2013 edition, and the practical differences for a homeowner are small but worth knowing.
| Area | Effect |
|---|---|
| eGuide software | Compliance sheets now carry more information and an illustration of the compliant arrangement |
| Configurations covered | Broader range of standard cases, so fewer jobs need a bespoke design |
| Documentation | Clearer output, easier to check against what was actually built |
If a firm hands you a compliance sheet produced under the old edition, that is not automatically a problem on an existing structure, but new work should be to the current guidance.
Checking the scaffold matches the sheet
The compliance sheet describes what should have been built. Three things a homeowner can check without technical knowledge:
- Bay length. Are the standards spaced roughly as the sheet says?
- Tie frequency. Are there ties where the sheet shows them, and have any been removed?
- Bracing. Are the diagonals present at the pattern shown?
If the built scaffold visibly differs from the sheet, ask why. There may be a good reason, and there may not be.
Why this matters to a homeowner
You are not buying an engineering document. You are buying evidence that the structure your roofer will stand on was selected against published limits rather than assembled by eye.
On a straightforward house scaffold that evidence takes a scaffolder about a minute to produce. A firm that cannot, or will not, is telling you something useful about how they work.
Next steps
Get an itemised estimate for your job in under a minute. No sign-up, and your details are never passed to a supplier unless you ask.