Temporary roof (weather protection roof)
A temporary roof of aluminium trusses and keder sheets carried by the scaffold, keeping rain off open roof structures and work areas.
Also called: weather protection roof, keder roof, scaffold roof, temporary roof system, encapsulation
When the old roof structure lies open during re-roofing, it must not rain in, not even at night or over the weekend. That is the job of a temporary roof: a provisional roof over the building or work area, carried by the scaffold. Work continues underneath regardless of the weather, materials stay dry and the building fabric is protected. Typical uses are roof refurbishment, heritage work, removal of hazardous materials and work on bridges or industrial plants.
The keder roof has become the common solution. Its name comes from the keder, a thickened bead along the edge of the sheet that is drawn into a rail and holds the sheet taut and storm-proof.
Components
- Roof trusses: aluminium trusses similar to a lattice girder, with keder rails in the top chord, assembled into duo-pitch or mono-pitch roofs.
- Ridge pieces and bearings: join the trusses at the ridge and transfer loads into the scaffold standards.
- Ledgers and bracing: longitudinal ledgers, diagonals and wind bracing keep the trusses spaced and stiffen the roof.
- Keder sheets: drawn in between two trusses and then tensioned.
Smaller jobs can use simpler solutions: weather posts on the top lift with sheets stretched over them, or extended standards on a modular scaffold carrying a flat sheeted roof. Large spans and rolling roofs that slide across the building always need their own design.
Erection
- Have the structure designed first: span, wind, snow where relevant and ties are calculated in advance. No design, no roof.
- Erect the supporting scaffold and tie the top lifts strongly, often far more than in the standard configuration, with tension-proof joints secured by drop-lock pins.
- Pre-assemble trusses with ledgers and diagonals into roof bays on the ground.
- Lift the bays in by crane or slide them across the scaffold bay by bay, seat them on the bearings and secure them.
- Draw in and tension the sheets, fix them at the eaves and close gables and sides.
On dismantling: sheets first, then trusses, extra ties last.
Risks and checks
- Wind suction: a roof is not only pressed down but lifted, so standards and ties below must take tension.
- Snow and water: many temporary roofs are not designed for snow load. Clear snow and avoid ponding with extra ledgers or better tension.
- Open sides let wind push the roof from inside; sheet the ends as well.
- Dented or bent keder rails stop the sheet running or release it in a storm.
On used systems, inspect chords for dents, welds for cracks and rails for damage, sheets for tears and frayed keders. A used roof system only makes sense with complete documentation and a matching design. A competent person inspects scaffold and roof together before handover and again after storms. Heritage projects are covered in our guide to renovating old and listed buildings.