London spoils us for choice when it comes to museums and galleries. When one of the jewels in the capital’s crown needed a roof refurbishment, the task was not only to protect the museum’s priceless collection of artwork and artefacts but to extend the service life of the attraction’s Grade I Listed building too.
Maintaining the museum’s complex network of roofs is critical to protecting both the building and its valuable exhibits, as well as ensuring a safe and comfortable place for staff and visitors. As part of a wider programme of upgrade and maintenance works, a roof refurbishment was required for multiple roof areas of the museum, which were nearing the end of their service life.
Although the existing roof coverings were largely asphalt, the requirement was for a liquid-applied waterproofing membrane that could tackle the complex detailing requirements for the roofs while providing a high-performance retrofit solution compatible with the existing roof covering. A liquid system also had the advantage of overcoming the need for hot works, which, given the heritage and financial value of the building and its contents and the need for the museum to remain open to the public while the work was carried out, significantly reduced risk.
Specialist roofing supplies merchant, Chandlers Roofing Supplies, recommended the use of Carlisle’s Arboflex PU; a moisture-activated liquid waterproofing system that usually requires no primer, is compatible with most existing roof coverings and provides speed and ease of installation for flat roofs and semi-pitched roof areas. Roofing contractor, Martin’s Roofing, was appointed to carry out the project, leveraging the company’s experience in heritage refurbishment and liquid systems, and the team was trained in the installation of the Arboflex system by the Carlisle Academy.
The project was delivered in three phases, with phase one comprising an overlay of new Arboflex waterproofing onto seven gallery roofs, phase two an overlay of drainage outlets, walkways and gulleys on domed roof areas and phase three the installation of a warm roof build-up for the photographic gallery, following asbestos removal and installation of new steelwork and a new roof deck.
The first phase of the roof refurbishment involved seven roofs with a 45º pitch, totalling an area of around 600m2. Each roof has 30m-long glazed sections on one side with an asphalt roof covering on the other, leading to a drainage gulley.
The glazing was covered by boards to protect it during the roof refurbishment and the Martin’s Roofing team prepared the roof, using Carlisle’s Arboflex PU sealant to repair any cracks in the asphalt prior to installing the Arboflex liquid waterproofing as an overlay.
No primer or vapour control layer was required, but the contractor mixed Carlisle’s thickener with the Arboflex liquid and left it to stand for an hour to provide the viscosity required for the pitched areas. The Arboflex liquid was rollered onto the roof, and the system’s glass fibre matting was laid onto the wet membrane prior to the application of more liquid in a wet-on-wet installation process. This included complete encapsulation of all the gulleys, which lead to external drainage outlets. Once the membrane had cured, Carlisle’s U/V protection topcoat was applied, taking the installation from a 10-year system to a BBA-accredited, 20-year service life.
The domes on the roof areas involved in phase two of the installation do not require a waterproof covering, so this phase was entirely made up of complex detailing. The Arboflex liquid waterproofing system was an ideal solution for this because it can be applied accurately to the contours of the roof surface. This included taking the waterproofing 200mm up the vertical stonework, with no primer or vapour control layer, and applying it directly onto the roof surface. The Arboflex system was applied around the base of each dome, on the gulleys and to the upstands. The Martin’s Roofing team then dressed the upstands with traditional lead flashings, providing dual protection against water ingress, along with a heritage aesthetic.
Robust new roof
For the photographic gallery, the requirement was for a completely new warm roof build up, following the installation of new steelwork, sound-proof panels, and a ply roof deck by Quinn London.
The installation team began by applying Carlisle’s FG35 primer to the roof. Carlisle’s Alutrix 600 vapour control layer was then laid onto the wet primer, with its bituminous face down and aluminium face up, prior to the installation of 160mm PIR insulation board. The PIR boards were then primed, and the installation team laid an Arboflex carrier membrane onto the insulation, with 50mm laps, to create a smooth finish that avoids any joins between the boards from being noticeable through the waterproof membrane. Finally, the Arboflex PU liquid waterproofing system was installed in a wet-on-wet process, and Carlisle’s U/V protection topcoat was applied to the cured system to achieve the 20-year guarantee.
The photographic gallery phase included extensive detailing to accommodate the rooftop plant and equipment installed onto the completed roof, including around 50 stanchions rising through the roof as fixings for mechanical plant and screens. The detailing requirements also included adapting the drainage to improve resilience against standing water while working with the original building design, with channels cut into the brickwork at the gable ends to provide additional rainwater drainage to the existing gulley and four outlets.
Dean Martin from Martin’s Roofing comments: “The goal has been to protect the aesthetics and integrity of the building while delivering a robust defence against water ingress and delivering a low-maintenance solution. The Arboflex PU liquid waterproofing system has fulfilled all these goals. There have been zero issues with water ingress, despite subsequent storms and torrential rainfall.”