Scaffold Technical Guide • TG9:18 • Weather Protection
What Is a Temporary Roof Scaffold?
A temporary roof scaffold is a scaffold-supported roof structure used to protect an exposed building, work area or roof opening from weather while construction, refurbishment, re-roofing or structural work is carried out below. It is commonly formed from supporting scaffolds, roof beams, bracing, sheet rails, roof sheets and weather-protection sheeting.
Temporary roof scaffold layout
Definition
What is temporary roof scaffolding?
Temporary roof scaffolding is a temporary works structure that creates a protective roof over an exposed area. It is used when a building, roof structure, loft area, extension, heritage roof, chimney area or refurbishment zone needs protection from rain, wind exposure or weather-related delays.
The roof may be a mono-pitch, duo-pitch, span roof, rolling roof or temporary enclosure depending on the site. The structure is normally supported by scaffold towers, independent scaffolds or a surrounding support scaffold, with the roof formed from beams and sheeted roof covering above.
Technical Layout
How a temporary roof scaffold is built
A temporary roof scaffold is built around the span to be covered, the pitch needed for water run-off, the support scaffold arrangement and the weather exposure on the site. The roof must be supported, braced and restrained so it can deal with vertical loads, lateral loads and uplift forces.
The roof normally bears onto scaffold towers, independent scaffolds or support scaffolds set out to carry roof loads.
Lattice beams or proprietary roof beams form the main span and support the roof covering.
Sheet rails or purlins support the sheeting and help maintain the roof profile.
Sheeting may include keder sheets, corrugated sheets or other temporary roof coverings selected for the system.
Plan bracing, façade bracing and roof bracing help resist movement and keep the roof stable.
Ties, anchors, buttressing, kentledge or other restraints may be required depending on the design.
Types
Common temporary roof scaffold arrangements
Temporary roof scaffolds are not all the same. The correct arrangement depends on the building footprint, the opening to be protected, the available support points, the required access below and whether the roof needs to move during the works.
A one-way fall used where drainage can be directed to one side and the span allows it.
A two-sided pitched arrangement used where water needs to be shed towards both eaves.
Used where the temporary roof spans between scaffold supports or towers.
A rolling roof can allow phased access, lifting operations or staged work below the roof line.
Planning
What needs to be checked before installing a temporary roof?
A temporary roof should be planned around the building geometry, span, pitch, sheet type, roof loading, side sheeting, wind exposure, snow loading, restraint arrangement and the works taking place underneath. Small changes to sheeting or enclosure can change the forces acting on the scaffold.
- Span: the distance between supports determines the roof beam arrangement and loading.
- Pitch and fall: the roof needs enough fall to shed rainwater and reduce standing water risk.
- Wind uplift: roof sheets and side sheeting can create uplift and suction forces that must be considered.
- Snow loading: the roof may need to account for snow load depending on exposure, duration and design requirement.
- Support scaffold: the scaffold below must be able to carry vertical and horizontal forces from the roof.
- Restraint: ties, anchors, kentledge, buttressing or other restraint may be needed to control movement.
- Drainage: eaves, gutters, sheet laps and run-off direction should be considered before erection.
- Sequence: the erection method, lifting method, rolling arrangement or sheet installation sequence affects the temporary roof setup.
Technical References
TG9:18 temporary roof guidance
NASC TG9:18, also written as TG09:18, is the main technical guidance for the design and construction of temporary roofs and temporary buildings formed with scaffolding. It is relevant to the planning, design, construction and dismantling of temporary roof structures.
The principal NASC guide for temporary roof and temporary building structures formed with scaffolding.
Relevant to scaffold performance, working platforms and temporary access scaffold principles.
Relevant where snow loading must be considered by the temporary works designer.
Relevant where wind pressure, suction and uplift forces need to be calculated.
Relevant to temporary works management, coordination and design-control procedures.
Proprietary temporary roof systems, keder systems and roof sheets should follow the relevant manufacturer information.
Limitations
When is a temporary roof more technically demanding?
Temporary roofs become more demanding when the span is large, the roof is high, the building is exposed, the sides are sheeted, the scaffold is close to neighbouring structures or the works need phased access below. Wind uplift and internal pressure can be significant where sheeting encloses the scaffold.
- Large spans: longer spans increase roof beam demand and support reactions.
- High exposure: open sites, coastal areas and elevated roofs may increase wind effects.
- Sheeted elevations: side sheeting can change pressure and suction on the roof structure.
- Rolling roofs: moving components need careful sequencing and support planning.
- Complex support: cantilevers, bridging, weak ground or irregular buildings may require design input.
FAQ
Temporary roof scaffold questions
Is a temporary roof scaffold the same as a normal scaffold?
No. A temporary roof scaffold is specifically arranged to support a roof covering. It must account for roof span, pitch, sheeting, wind uplift, weather exposure, drainage and support reactions.
What is a tin hat scaffold?
“Tin hat” is a common trade term for a temporary roof scaffold. The phrase usually refers to a scaffold-supported roof cover used to protect an exposed building or work area.
Does every temporary roof need design input?
HSE identifies temporary roofs as normally requiring bespoke design. Outside recognised standard configurations, competent design and calculations are required.
Can a temporary roof be moved?
Some temporary roofs are arranged as rolling roofs, allowing sections to be moved for phased work, lifting operations or staged access. This needs to be planned into the roof arrangement.
Need a temporary roof scaffold assessed?
BlackFox Scaffolding can assess whether a temporary roof scaffold is suitable for re-roofing, loft works, structural openings, heritage roof works, extensions, weather-sensitive refurbishment and exposed building works.