B. BIRD Whitby & Bird

The two tower blocks of Gelston Point and Winterton House built at the end of the 1960’s utilised alt the latest ideas for speedy construction: calcium chloride to speed up setting up of the concrete; sprayed asbestos protected steel frame; precision GRP cladding panels made weathertight by mastic joints. They have gone badly wrong and are deemed uninhabitable and abandoned except by squatters. The proposal is to demolish one and retain the other. To be socially acceptable the retained block must avoid the mistakes of the past and not only look solid and durable but actually be so. The proposal here is to use thick self supporting masonry. The extra load from the brickwork has to be carried on new piles and pile caps. The steelwork has to be protected by a simple waterproof system such as bitumastic paint but this will act as a debonding membrane. Lugs are therefore welded to the steel to ensure that the steel and brickwork are fully bonded together. Once the masonry and the steelwork are intimately bonded together, they move together and the need for movement joints disappears. The building needs insutation and so it is proposed to use a derivative of the SUM (Single Leaf Insulated Masonry) details developed by BCRA for low rise housing. There are, however, inevitable cold bridges where steel passes through the insulation and these details have not been used for high rise housing before so a programme of testing is required for this and for rain penetration under driving rain conditions. There is an enhanced loadbearing capacity so more floors may be added. Preliminary costing shows the thick self supporting masonry solution to be cheapest.