Extraordinary Roof - The project they said could not be done

Proteus Waterproofing has completed one of its most challenging projects – a contract which some experts said could never be done - at the Cromwell Galleries, located in the heart of South Kensington’s Museum district and housed within five Grade II listed buildings, stretching across 35,000sqft.

They were originally designed in 1858 by Sir Charles James Freake and through delicate restoration, these Georgian townhouses have been individually renovated to create permanent and shared offices, temporary exhibition space, viewing rooms, art storage, technician hire, working facilities and a Club Room where some of the most established collectors, dealers, curators, and arts professionals can collaborate and flourish.

The Cromwell Galleries is an extraordinarily elaborate roof which features a unique trapezoid shape, made up of seven welded frames held together with over 1,500 weather screen metal support brackets, a massive challenge for the Proteus Approved Contractors, Infallible Systems Ltd and one which other manufacturers and contractors said could not be delivered.

The design also incorporated a major new build section which delivered its own particular challenges, requiring just the right level of insulation below the timber roof deck as well as above to meet U value requirements and overcome any condensation risk.

An Insulated Built Up Roof system was chosen as the perfect waterproofing solution to ensure that all of the complex detailing and shapes could be easily and effectively protected.

At every stage, Proteus Waterproofing worked closely with the roofing contractor, the main contractor and the architect to assist with the design and installation of the waterproofing. Prior to work commencement, Proteus also conducted a roof survey, once the timber roof deck was installed, providing a comprehensive condition report and bespoke specification for the proposed roof system.

This was supported with detailed drawings showing how to install the system to and around the 1,500 metal fixing brackets for the rain screen cladding giving the client a full understanding of all of the issues such as the critical gaps between the roof deck and the bracket fixings for the rainscreen to ensure the right levels of protection and insulation were achieved.

Design meetings were carried out with the Proteus Technical Department to ensure that all applications, thermal performance and regulations were achieved, taking into consideration the insulation thickness and the limited heights of the weather screen bracket fixing holes.

Detailed drawings and work installation plans were afterwards put in place to run alongside the weather screen contractors to ensure a complete understanding from all trades involved on these complex roofing works.

This was a major consideration as the project potentially offered several design and installation hurdles, in particular, the Gallery’s trapezoid shaped main roof which consisted of standing pitched roof lights and vertical walls, leading to ground level.

The first step was to prime all 1,500 metal rain screen cladding fixings by dipping them in metal primer. These fixings were then dipped again to ensure a seamless finish, while effectively encapsulating both the roof and the fixings.

The north light designed roofs were individually waterproofed and a Self-Adhesive membrane was installed over the primed, plywood roof deck, and cut into individual pieces to allow installation around the fixing brackets and the challenging detail areas. Thermal pads were installed under each metal fixing bracket to hold the weathering screens.

A vital part of the works was to ensure that every stage of the process was well organised and remained on schedule to allow the screens to be installed. This included PIR Insulation boards which were measured and cut around the fixing brackets, then dry laid to ensure correct positioning. They were then adhered to the AVCL with Foaming adhesive, removing gaps that could result in cold bridging. To prevent the insulation board bonding incorrectly to the AVCL, and the insulation build up from sliding down the roof, a stop end was fixed at the bottom of the pitched roof.

A Carrier Membrane was cut into individual sections to allow installation around the fixing brackets and window frame details. Once the built-up insulated installations were complete, the fully reinforced waterproofing system could be installed.

Firstly, an embedment coat was applied to the upstand underneath the window openings, terminating under the windowsill. This had to be applied around the window openings first to ensure that the EDPM window membrane could be adhered to achieve termination. Each individual roof section was embedded, followed by a final application of Top Coat, leading into the central and perimeter box gutters.

High level link bridge roofs above living spaces were designed with a Cut to Fall Insulation Scheme to ensure sufficient rainwater drainage into central channels, incorporating the metal fixing brackets.

These brackets were encapsulated with a Vapour Control SA before Tapered Insulation PIR was installed in conjunction with detail/bracket heights. Each individual tapered insulation board was carefully measured and cut to accommodate the fixing brackets, while ensuring the fixings holes in the brackets were above the insulation/waterproofing surfaces.

Tapered scheme finishes were then overlaid with the Carrier Membrane SA and adhered with primer, before being fully encapsulated with the waterproofing. All metal fixing brackets were coated with Epoxy Primer before dressing with the waterproofing. A Top Coat was applied to all areas of the flat roofs and detail areas.

A concrete lift overrun roof located in the lower basement area was overlaid with a Carrier Membrane SA and adhered with primer to provide a reinforced, waterproofing layer. Cold Melt® waterproofing was applied to these tight accessible areas because of its cold applied, odourless properties and ease of application. These areas are used for M&E and required a buried waterproofing system that can withstand the weight of concrete slabs on pads and machinery. A Low-K Water Reducing Layer was installed under the slabs to protect the waterproofing. All waterproofing was leak tested to eliminate any damages and penetrations.

To ensure the project was completed to the highest standard, it was crucial that the main contractor, Infallible Systems Ltd, Proteus Waterproofing, and all design/installation teams maintained regular contact. Weekly site inspections were carried out by Proteus Waterproofing to inspect the progress and installation of the works, offering product and application advice where necessary. Photographs were taken throughout each stage to evidence the high-quality installation of the BUR/waterproofing layer.

On completion, all sections of the roof were leak tested to eliminate any breaches in the waterproofing. A sign off report which included details and photographs of the finished works was issued, enabling the contractor to apply for a guarantee on behalf of the client.

Proteus Waterproofing only supplies products to contractors whose operatives are of a suitable skill level and have demonstrated their competence at product training events. Installation guidance, product datasheets and material safety datasheets are provided to all contractors who have attended these programmes and, as a result, been issued with a Proteus Approved Installer card.