Birdcage and interior scaffolding: working under ceilings, in halls and large rooms
On a facade, a scaffold grows upwards and leans on the wall. Under a ceiling it is the other way round: the working area spreads sideways, often across a whole room, and walls are available only at the edges. Ceiling plaster in a Victorian stairwell, repainting a sports hall, ductwork in a warehouse, restoring a decorated ceiling in a church: this is the territory of the birdcage scaffold. It follows rules of its own.
Birdcage, interior scaffold, mobile tower: the terms
- Birdcage scaffold: the British term for a scaffold with a large, continuous working platform, usually at one level below a ceiling, carried by a grid of standards and ledgers.
- Interior or space scaffold: a structure that extends in all three directions, for instance around a vault, a dome or a machine, often with several platform levels.
- Mobile tower: a tower on castors to EN 1004 with a limited platform size, ideal when the working position changes often. An alternative to a birdcage, not part of one.
Birdcage and interior scaffolds are working scaffolds under EN 12811-1, so the usual principles on load class, edge protection, access and inspection apply.
Typical uses
- Plastering, drylining or painting in tall rooms, such as period houses with 3.5–4.5 m ceilings or open galleries.
- Stairwells, often scaffolded over several levels in the well, with irregular plans.
- Halls and sports halls: ceiling paint, acoustic panels, lighting, sprinklers or ducts at 6–12 m.
- Churches and historic rooms: restoration of plasterwork, murals or vaults, with gentle base details.
- Industrial plant: work on vessels or crane rails, often built around obstacles.
Choosing the system
A birdcage needs ledgers and decks in two directions. A modular scaffold with rosettes or similar nodes does this best, because ledgers connect in several directions at every node and the grid can be chosen freely in both directions. Frame scaffolds can be placed side by side and joined with tubes and couplers, but are less flexible and use more material.
| Criterion | Birdcage (modular) | Frames side by side | Mobile tower |
|---|---|---|---|
| Area | medium to very large | small to medium | small, local |
| Continuous platform | yes | possible with extras | no |
| Fitting to the floor plan | very good | limited | not needed |
| Erection time | high, but once | medium | low, frequent moves |
| Passage underneath | can be planned | difficult | not relevant |
Example: painting a 7 × 6 m living room ceiling at 4.2 m is usually quicker from an aluminium mobile tower moved two or three times; compare facade scaffold or mobile tower. Fitting an acoustic ceiling in a 30 × 18 m sports hall at 8 m over several weeks justifies a birdcage, or several large islands moved section by section.
Getting the deck height right
Under a ceiling, deck height is the key dimension. Too low and the operative works with arms stretched on tiptoe; too high and they stoop. A distance of about 1.8–2.0 m from deck to ceiling works for most people. Long-handled tools or spray equipment allow a little more, fine restoration work a little less, and beams and services need extra headroom.
Example: a hall has 7.20 m clear height to the soffit. At 1.90 m clearance the deck sits at 5.30 m. On a modular scaffold with nodes every 0.5 m, the deck height is set via standard lengths and base jacks. Where ducts hang down to 6.40 m, the clearance there drops to 1.10 m, so either a second, lower platform is built locally or the whole deck is lowered.
Stability without wall ties
A facade scaffold is narrow and held by the wall. A birdcage is wide and often stands free. Its stability comes from three things:
- Geometry: the wider relative to its height, the more stable. A birdcage 12 m wide and 5 m high is uncritical in this respect; a strip 2.5 m wide and 8 m high is not.
- Bracing in both directions: vertical diagonals lengthways and crossways stop the grid racking; horizontal diagonals in the deck level and often at the base keep bays square. How many bays one diagonal braces is set by the manufacturer's instructions.
- Connection to the building: where possible, hold the scaffold to walls, columns or beams with tubes and couplers or ties, even at a few points.
Indoors, wind is largely absent as long as doors and large openings stay closed. Horizontal forces still arise from overhead drilling, moving material and small out-of-plumb errors. In open halls with large doors, wind is very much a factor. Not every manual covers birdcages; if it does not, or the structure is tall, irregular or multi-level, an individual design is needed.
Floor loads
Indoors, the floor is often underestimated: screed, tiles, parquet, floorboards or a slab over a basement all have limits. A grid of 3.07 × 2.07 m gives about 6.4 m² per bay. Load class 3 stands for 2.00 kN/m², so a fully loaded bay carries roughly 12.7 kN. An inner standard collects a quarter of each of four bays, so again about one bay's worth, plus the scaffold's own weight above. Well over a tonne can arrive at the foot of one standard, on a small base plate.
- Spread the load with boards or timbers under every base jack; see sole board.
- Have someone with structural knowledge confirm the capacity of timber floors, raised floors, basement slabs and car parks.
- Protect parquet, stone and historic floors with fleece and boards before the sole boards go down.
- Choose the load class to suit the work; painting needs less than plastering with material on the deck. See load classes and width classes.
Decking, edges, access and the build sequence
The platform should be fully decked and locked; a missing board is a hole. Keep the gap to the wall at about 30 cm or less, otherwise fit edge protection there. Every free edge, including stairwells, galleries and openings in the deck, needs full edge protection: two rails and a toe board. Large areas are better served by a stair than a ladder, and very large ones by two accesses. Where people pass underneath, close-board the deck or add a fan. Keep emergency exits, extinguishers and smoke vents clear and agree this with the building operator.
- Survey plan, clear heights, beams, lights, services, columns and openings.
- Set the grid so columns fall between standards and make-up bays at the edges stay small.
- Protect the floor, confirm capacity, lay out sole boards.
- Build the base level with ledgers in both directions and level it precisely; errors here carry upwards.
- Take standards and ledgers up lift by lift, bracing both ways.
- Deck, lock, close make-up bays, fit edge protection.
- Install the access, inspect, tag and hand over.
The scaffolding calculator gives a rough parts list, to which you add braces and edge protection. Among new systems, CETRAC's modular MODUX will be available from 2027, with the approval procedure not yet completed; details on new CETRAC scaffolding.