When Make Architects needed a waterproofing solution for their latest project in the City of London, they turned to IKO PermaTEC hot melt. Here, SIG Design & Technology set out why this was a particularly challenging roofscape.
5 Broadgate is truly a “groundscraper”, a term coined by the FT as it announced the unveiling of the UBS new City of London headquarters in May 2006. Just 12 storeys of offices yield over 65,000m2 of high-spec office space, including four football pitch-size trading floors and 7,500m2 of concrete-decked roof and terraces.
Waterproofing such an expansive and complex roof has its particular challenges and required, a reliable detailing delivered by contractors who could work within the given timescales. The choice of waterproofing was to perform for a minimum of 30 years, be cost effective and also contribute towards the building’s design stage BREEAM Excellent rating.
The speed of the hot melt waterproofing application meant that Make was able to complete sequential quality inspections safe in the knowledge that the waterproofing would then be protected immediately following the installation of the insulation and subsequent pouring of the concrete slab.
Sustainable credentials of hot melt
As well as being cheaper, easily installed and having a longer lifespan, IKO PermaTEC also offered other advantages to the client. The product is manufactured in the UK at a factory in Derbyshire giving it efficient carbon delivery miles. It is produced with zero wrapper waste which reduces on-site waste, making a small contribution towards British Land’s ‘Zero Waste to Landfill’ commitment and towards BREEAM Excellent for the project at design stage.
Inverted roof build up at 5 Broadgate
The waterproofing is part of a 600mm roof over-cladding build-up consisting of a 200mm concrete slab, a 7.5mm hot-melt rubberised bitumen membrane, a 200mm thermal extruded insulation and drainage mat, and a 150mm floating slab.
The PermaTEC system consists of a high penetration primer, two coats of the 3mm PermaTEC waterproofing membrane with a PermaFLASH-R reinforcement layer in between, and the PermaGUARD-F protection sheet. These layers were all applied before the installation team began work on the next adjacent area. Unlike many cold applied liquids, there is no need with hot melt to wait until each layer hardens.
Electronic leak testing during construction
Fifteen minutes after the hot melt was applied to the roof, electronic leak testing was carried out to identify any problems and localised repairs made. This was followed by installation of an extruded polystyrene insulation board – Roofmate SL-A – then an IKO Plasdrain 6 loose-laid drainage mat. The build-up was topped by the overslab of 150mm poured concrete, with pavers and ballast used in areas of light traffic.
Vertical roof penetrations
One challenging aspect at 5 Broadgate was designing waterproofing solutions for around 100 vertical roof penetrations created by perimeter structural steel elements, posts and columns.
Cross brace waterproofing
For six tricky cross-brace connections, a special solution was required for the junction between columns and cross bracing, to avoid any potential pooling water, despite a pitch pocket detail. The solution was IKO’s Polimar EC/UV cold-applied liquid waterproofing around the connection plate, over the PermaTEC pitch pocket.
A team effort
5 Broadgate was awarded a BREEAM Excellent rating at design stage, with the roof achieving a U-value of 0.20. This helped contribute to the project’s energy conservation levels being nearly 50% better than regulations require. The project will be completed in the summer of 2016.