Scaffold Access Stairway Calculator — Tower Dimensions & Rest Platforms

Stairway towers should be used when: the scaffold will be used by many workers (more than about 10 people regularly), workers need to carry tools or materials up (you cannot carry items safely on a ladder), the scaffold height exceeds 9m, or the scaffold will be in use for extended periods. Under CDM regulations, the access must be suitable for the number of users.

As a practical rule of thumb, provide a rest platform roughly every 4.5m of vertical rise — and always at each lift level where the tower ties into the scaffold. Proprietary stair towers place a half-landing at every ~2.0m lift, so in practice you get a landing at every flight. NASC SG25:20 and the stair-tower manufacturer's drawings govern the actual landing positions; Approved Document K limits a building stair flight to 16 risers (around 3m) as further context. Each landing should be large enough to allow the direction of travel to reverse safely.

Typical scaffold stair tower dimensions: 1.4m wide × 2.5m long in plan. This accommodates a 700mm clear stair width with a 180° turn at each landing. Some manufacturers offer narrower (1.2m × 2.0m) or wider (1.8m × 3.0m) options. The tower must be tied to the main scaffold or the building at each landing level.

For ladder access within scaffolds (per NASC SG25:20): an internal ladder run is limited to a maximum of three 2.0m lifts (6.0m) between landings, and an external ladder to two lifts (4.7m). The ladder must extend at least 1.0m above each landing to give a handhold. Trap doors must be provided in the platform for internal access. Ladders should be pitched at 75° (a 4:1 ratio) with uniformly spaced rungs. SG25:20 also recommends more frequent rest platforms, and ladder access is only suitable for low-use scaffolds with few workers.

Stair towers should be founded on the same base as the main scaffold — typically sole plates on firm ground. If the stair tower is freestanding (not attached to the main scaffold), it needs adequate bracing and ties to the building. The base must support the concentrated loads from the stair tower standards, which carry the weight of all the stairs, landings, and users.