Compliance · 8 min read

Scaffolding load classes explained: Class 1 to 6 with real examples

Get the load class wrong and one of two things happens: the scaffold is overloaded and dangerous, or it's over-specified and you've priced yourself out of the job. Load classes look like a simple table, but the arithmetic behind bay loads, board widths and which trades need which class trips up more scaffolders than any other part of TG20:21.

This guide walks through classes 1 to 6 with real numbers, so you can check a bay load yourself rather than trusting a rule of thumb. For how load class interacts with tie patterns, see our TG20:21 compliance guide.

The six load classes

Rule of thumb for pricing conversations: painters and light trades sit at Class 2, general trades (render, cladding, most roofing) at Class 3, and bricklayers push you to Class 4. Anything above that is specialist and usually needs the loading confirmed with the principal contractor before you quote.

From kN/m² to an actual bay load

The kN/m² figure is a uniformly distributed load, it needs converting to a real bay load before it means anything on site. A standard scaffold bay is commonly 2.0 m long with a boarded width of around 0.9 m (four standard scaffold boards at 225 mm each, allowing for overlaps), giving a working platform area per bay of roughly:

2.0 m × 0.9 m = 1.8 m² per bay

Multiply that area by the load class to get the maximum total load that bay can safely carry:

That last figure already includes the weight of anyone standing on the bay, so a Class 4 bay carrying two bricklayers (say 160 kg combined with tools) has roughly 390 kg of stored materials headroom left. A little under two packs of standard bricks, which weigh around 1,000–1,200 kg per pack. In other words, a full pack of bricks landed on one bay of a Class 4 scaffold is already close to or over the limit for that bay alone, even before you add the bricklayers. This is exactly why materials get spread across several bays rather than dropped in one place.

Board width matters too

The kN/m² figures assume a standard boarded width. Widen the platform. Double boarding for storage, or a loading bay with extra board width, and the area per bay goes up, which increases the total load the bay is asked to carry even at the same class. A loading bay boarded out to 1.8 m width instead of 0.9 m doubles the area, and therefore doubles the load a Class 3 rating implies for that bay. Which is one reason loading bays are usually treated as a bespoke element rather than folded into the general load class; see our guide to loading bays, temporary roofs and birdcages.

Overloading mistakes that actually happen

• Quoting Class 2 for a job that turns into blockwork . The trade changes mid-contract but the scaffold spec doesn't.
• Multiple lifts loaded at once, TG20:21 restricts how many platforms can be simultaneously loaded at higher classes; two fully loaded Class 4 lifts stacked above each other is not the same as one.
• Materials stacked in one bay instead of spread out . A full pallet dropped by a crane onto a single bay rather than distributed, as the worked example above shows.
• No load class stated on the tag, the site team assumes the highest class "just in case" or, worse, doesn't think about it at all.
• Boarding widened without re-rating the bay, extra boards added for convenience without recalculating what that does to the load per bay.

Common questions

Can a scaffold have different load classes on different lifts?

Yes. A common approach is to rate the working lift for the trade in use and a lower class above or below it, provided the tie pattern and standards are specified for the highest class actually in use and the compliance sheet reflects it.

Who decides the load class for a job?

The scaffolding contractor sets it based on the trades and materials the client confirms will be on the platform, always confirm this with the client before pricing, since underestimating it is a common cause of disputes when a heavier trade turns up unannounced.

Is a higher load class always safer?

It's more conservative for loading, but not automatically "safer" in every sense, over-specifying pushes up standard spacing requirements, tie counts and cost, and can also mean over-representing what site teams think they're allowed to do.

What board width is assumed for standard load class figures?

TG20:21's standard figures generally assume the typical boarded width for the scaffold type (commonly four boards, around 0.9 m). Wider boarding or loading bay areas need their own assessment rather than assuming the same class applies unchanged.

TG20:21 is a trademark of the National Access & Scaffolding Confederation (NASC). Figures given are typical/indicative, always confirm exact loadings for your configuration against the current TG20:21 eGuide output.