Scaffold Design Load Calculator — Dead, Imposed & Wind Loads

Three main loads: (1) Dead load — self-weight of the scaffold (tubes, boards, fittings). This is built up from real component masses (48.3×4.0 EN39 tube ≈ 4.4 kg/m, board ≈ 0.25 kN/m² of boarded area, plus fittings); the ~0.3 kN/m² per boarded lift used here is an indicative planning estimate only. (2) Imposed (service) load — workers, tools and materials on the platforms (0.75-6.0 kN/m² depending on load class, per BS EN 12811-1 Table 3). (3) Wind load — horizontal force from wind pressure acting on the scaffold face and any sheeting/netting.

TG20:21 (which supersedes TG20:13) is the NASC (National Access & Scaffolding Confederation) technical guidance for tube and fitting scaffolding. A TG20 compliant scaffold follows standard configurations that have been pre-designed — if the scaffold fits within TG20 parameters (height, load class, tie pattern, base conditions) and a compliance sheet is produced via the TG20 eGuide, no bespoke design is needed. Scaffolds outside TG20 limits require a bespoke engineering design.

A scaffold needs a bespoke design (by a competent engineer) when it falls outside TG20 parameters: height over 50m, non-standard configurations (cantilevers, bridges, loading bays), fan or catch scaffolds, heavy-duty loading (Class 4+), sheeted scaffolds in exposed locations, scaffolds with incomplete tie patterns, or any unusual arrangement. The design must be by a qualified scaffold designer.

Wind creates horizontal loads that must be resisted by ties and bracing. An unsheeted scaffold has a low aggregate wind force coefficient (~0.3). Debris netting (~0.5) and especially full sheeting (~1.0) dramatically increase wind loads — this is why sheeted scaffolds need more ties and a specific wind design to BS EN 1991-1-4 / TG20:21. For working at height, the HSE advises that work should generally stop once wind speed exceeds about 23 mph (10.3 m/s, Beaufort Force 5) — mobile access towers around 17 mph — because winds above this affect a worker's balance.

A 48.3mm × 4.0mm wall scaffold tube (BS EN 39) carries a high compressive load over short lengths, but capacity is governed by the unsupported EFFECTIVE LENGTH between nodes — the lift height and brace spacing — not the overall scaffold height. As the lift height grows, buckling reduces the capacity. As an indication: at a 2m lift ≈ 25 kN, at 2.4m ≈ 18 kN, at 2.7m ≈ 14 kN. TG20:21 strut/standard tables give the design capacities for the actual configuration.