Smaller track cranes are usually used at roof level of the boiler house to complete the lighter steelwork for the roof and intermediate floors, and also to assist in dismantling the main derricks on completion.

Use is now being made of very long-reach mobile cranes, both crawler and lorry mounted, for erection of both main and infill steel members and for the annexes and auxiliary buildings. Jib lengths exceed 60 m and loads of 1001 are possible.

The manufacture and erection of the steel frame for the turbine hall is governed by conditions very similar to those applicable to the boiler house steelwork, except that it is not usual to use track cranes at roof level due to there being very little, if any, intermediate steelwork apart from the roof purlins which are easily placed by the main derrick.

19.4 ''Cladding

It would be extremely difficult to use an in-situ concrete roof and brick walls for the cladding of a modern 2000 MW power station and also conform with the present programme requirements. This, together with other factors including the higher loadings which would result from the use of concrete and brickwork, has led to the adoption of metal deck roof construction and light­ weight metal wall cladding.

For architectural reasons, and also to provide walls at a lower level which are more resistant to mechanical damage, it is usual to build the bottom 6 m to 12 m of the boiler house and turbine hall walls using brickwork, exposed aggregate concrete slabs or other similar material.