An SG4:10 compliant erection method is a vital to the safe and successful erection of any temporary roof. The days of scaffolders sliding out along the top chord of beams 'should' be long gone! There are three main erection methods which the scaffold design engineer must consider and discuss with the scaffolding contractor when designing a temporary roof:
1. Erect in-situ. This method is usually employed where there is another structure underneath the roof to stand on and work from safely whilst erecting the temporary roof above. Sometimes the 'other structure' may be an access birdcage erected by the scaffolding contractor for the sole purpose of erecting the roof, however this is totally dependent upon the site.
2. Roll-out erection. This method utilises an access scaffold at a gable end which follows the profile of the roof, allowing the scaffolders to work safely whilst erecting each frame of the roof. Complete bays are formed and then rolled out down the length of the roof on castors. The components vary depending on which roof system is being used, but the principle remains the same with each. One advantage of this temporary roof type is that the roof doesn't have to provide full coverage the entire time, a phased work plan means the roof can follow accordingly, meaning a smaller scaffold is required which could be more cost effective.
3. Craned-in. Sometimes seen as the safest method of temporary roof erection, as time spent working at height is minimised by constructing most of the roof at ground level. It is often the fastest method of erection, complete roof bays can be erected on the ground or even off-site and then lifted and fixed one after another - minimising the crane hire period. However it doesn't give the flexibility in access that the other two methods provide, and it also requires more bracing between the roof beams to maintain rigidity during the crane lift.
The final build-ability consideration is the sheeting method. The safest and fastest method is a Keder sheet system. Erected from an eave level platform and pulled through rails either within, or connected to, the top chord of the beam. It allows the scaffolders to work from a platform with edge protection and does not require them to traverse out along the beam. The installation of the Keder sheet can be tricky at first, but experienced and skilled scaffolders can do this relatively quickly. Other sheeting methods include fixing monarflex to wooden laths, clear or translucent plastic panels and probably the most popular for small scale mono-pitch roofs is corrugated iron sheets fixed with roofing couplers.
Part 3 will follow shortly covering 'Environmental' considerations.