Compliance · 9 min read
When a scaffold needs a bespoke design (and when TG20 is enough)
Most scaffolds you'll quote fit neatly inside TG20:21's compliant envelope. A compliance sheet from the eGuide is all the evidence you need. But a fair number of jobs quietly step outside that envelope, and pricing them as if they hadn't is where scaffolders lose money and, worse, put up structures nobody has actually checked.
This guide sets out where the line between "TG20 compliant" and "needs a bespoke design" sits, who produces a design, and what it typically costs. For what the compliant route looks like on paper, see our guide to the TG20:21 compliance sheet.
TG20 compliant vs bespoke design
TG20:21's Design Guide has already done the structural calculations for a wide range of standard tube-and-fitting scaffold configurations. If your job's dimensions, load class, tie pattern and exposure fit inside that pre-checked range, the eGuide confirms it and produces a compliance sheet, no separate engineering needed.
A bespoke design is a one-off structural calculation, produced by a qualified scaffold designer, for a configuration the eGuide doesn't cover. It typically includes drawings, load calculations, tie force requirements and any special sequencing instructions, and it's the only valid evidence of compliance once you're outside the standard envelope. A compliance sheet produced by forcing non-standard numbers through the eGuide isn't worth the paper it's printed on.
Situations that usually need a bespoke design
| Situation | Why it falls outside TG20 compliant |
|---|---|
| Sheeting or netting beyond standard envelope | Dramatically increases wind loading; often needs a closer tie pattern than the eGuide's sheeted range allows for the height/exposure |
| Bridging over an opening, roadway or obstruction | Introduces spanning members and point loads the standard guide doesn't model |
| Truss-outs / cantilevered sections | Load path departs from the ground and needs specific calculation of the cantilever and its counterbalance/tie-back |
| Loading bays | Concentrated point loads from hoists and stacked materials well above general access loading |
| Temporary roofs | Large horizontal areas catch wind uplift and rain loading that a vertical façade scaffold isn't designed for |
| Unusual or poor ground conditions | Sloping, made-up, or soft ground needs a specific base design, spreaders, grillages or piled bases |
| Exceptional height or length | Beyond the height/length range the eGuide's pre-calculated envelope covers |
Our guides to loading bays, temporary roofs and birdcages and TG20:21 tie patterns go into more detail on two of the most common triggers above.
Who produces the design
A bespoke scaffold design should be produced by a suitably qualified and experienced scaffold designer, someone with recognised structural design competence for temporary works, working to TG20:21's Design Guide and BS EN 12811. On larger or more complex contracts this sits within a formal Temporary Works framework, with a Temporary Works Coordinator (TWC) on the principal contractor's side reviewing and approving the design before it's built.
Many established scaffolding contractors have an in-house designer or a retained design consultancy they use for anything outside the eGuide's scope. Smaller firms typically buy this in per job from an independent scaffold design consultancy, a route worth setting up before you need it in a hurry.
What it costs
Design costs vary a lot by complexity, but as a typical/indicative range for 2026, expect:
- Simple bespoke design (single loading bay, small truss-out): roughly £250–£500.
- Moderate complexity (sheeted scaffold outside standard envelope, temporary roof): roughly £500–£1,200.
- Complex or large-scale design (major bridging, birdcage over an unusual span, poor ground with piled bases): £1,200–£3,000+, sometimes with a site visit and revisions built in.
Turnaround is typically a few working days for straightforward jobs, longer if it needs multiple revisions or a Temporary Works Coordinator sign-off cycle. Build that lead time into your programme, a design request made the week before erection is a common cause of delayed starts.
Instead of pricing design-dependent jobs by guesswork, build the quote in ScaffQuote and flag the design cost as its own line before you commit to a start date.
Worked example: loading bay tips it into bespoke
A contractor is asked to add a single loading bay to an otherwise standard Class 3 independent scaffold, 30 m run, two lifts. The loading bay itself, with its concentrated point loads from a hoist and stacked pallets, sits outside the eGuide's general compliant range, so the contractor gets a bespoke design just for the loading bay bay, at a quoted £380. Labour and materials for the loading bay addition come to roughly £650. Total additional cost to the client for the loading bay: £1,030, against a base scaffold otherwise priced as a standard compliant job. Quoting the design cost separately and upfront avoided an awkward conversation once the scaffold was already up.
Common questions
Can I just use a bigger safety margin instead of getting a design?
No. "over-building" a scaffold you're unsure about isn't a substitute for a design, because you have no calculation confirming the extra tubes and ties actually address the specific loads involved. If it's outside the eGuide's scope, get a design.
Does every temporary roof need a bespoke design?
In practice, yes for anything beyond the smallest domestic applications. The wind uplift and rain loading on a horizontal temporary roof area are well outside what a standard vertical façade scaffold envelope covers.
Who pays for the design, us or the client?
Convention varies, but most contractors pass the design cost through to the client as a distinct line item on the quote, the same way they'd pass through hire of specialist equipment.
What happens if we build to a bespoke design but then change it on site?
Any deviation from the design should go back to the designer for a revision or confirmation it's still acceptable. Building differently from an approved design without sign-off leaves the design invalid as evidence of compliance.
Flag design-dependent jobs before you price them
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TG20:21 is a trademark of the National Access & Scaffolding Confederation (NASC). Costs and timescales are typical/indicative for 2026 and vary by region, designer and complexity, always get a firm quote for your specific job.