CMYA Finalist

Employer: BAM Construct UK

Project: Tamesis

It may seem counterintuitive, if not downright perverse, to deliberately decide to start later than planned on site, but John Rabey was playing the long game on this 100,000sqft office block.

Appreciating that the client’s pre-letting of the building meant that timely completion was crucial, John changed the structural frame from concrete to steel, trading off the slower site start involved (because of the longer lead in needed to design and manufacture the steel) to gain an earlier and more certain frame completion date. The longer preconstruction period he used to progress the design and procurement of the whole building.

Fresh from a previous project where he’d been splashing through water on each floor for many months, John was determined to get early watertightness. He therefore decided to change the original design of a concrete plantroom and a lightweight single-ply membrane for the remaining three-quarters of the roof in favour of a concrete roof throughout, topped by a hot liquid membrane. It made the building pretty much watertight once the concrete slab had been poured, simplified the interface details, and speeded up the start of internal works.

He also saw the danger of locating a 40,000-litre water storage tank at the site entrance. Not only would it restrict deliveries through the sole access road for a long period while the necessary temporary works were undertaken, but its installation nine metres below ground level would have required extensive dewatering on a site built on stilts to cope with historic flooding from the river just 200 metres away. Instead, he installed a longer, shallower tank at the rear of the project.

When he noticed some of the atrium’s installed upper glazing units exhibiting minor cracks, he immediately took action. Finding that the glass was cracking because it had to be installed in openings that changed shape as the frame was loaded out, he preloaded the frame with weights to create the final shape of the opening before the glass was installed, with the loads progressively released as the facade was built.