Victoria Ramwell from Kemper System explains the key considerations and advantages of specifying cold-applied liquid waterproofing for historical buildings
M any older properties feature different roof shapes with flat roofs – typically seen on extensions, or over porches and dormers. Although a flat roof may be less visible from the ground, it can still contribute to the character of a historic building, requiring specialist materials and workmanship.
When waterproofing a flat roof as part of a heritage refurbishment, a liquid-applied membrane may not always be front of mind for specifiers and contractors. However, the versatility of this modern technology means it can emulate traditional roof coverings, providing a cost-effective and durable solution.
Going green
As liquid-applied membranes can be manufactured in bespoke colours, this makes them ideal for heritage projects featuring aged copper roofs. Over time, the weathering process and exposure to moisture will change the chemical composition of the metal, turning the copper into a distinctive light green colour also referred to as ‘patina.’
By mixing different pigments during the manufacturing process, a liquid can be matched to roofs’ patina, providing the exact shade of green needed to achieve a consistent colour for both refurbishments and extensions.
In London, a building located in the heart of an historic 11-acre estate is one example of a property to benefit from liquid waterproofing. Property and construction consultancy Ingleton Wood specified a cold-applied liquid as part of the wider refurbishment of the building, which has been transformed into Grade A office space.
To emulate the appearance of the existing copper roof, the polyurethane liquid was manufactured to create the exact RAL 6034 colour code specified for this project. In this instance, the same liquid already featured on the roof, so it was overlaid with the new membrane to refresh the green colour. The refurbishment also required new roof areas to be waterproofed with the specially manufactured liquid.
As well as meeting specific design requirements, the liquid waterproofing generated further benefits for this project. It was quick and easy to install around the roof’s extensive detailing, including numerous pipe and ventilation penetrations.
Sandwiched between two other properties on a main road in London, meaning very limited access for the roofing contractor. As the liquid-applied system eliminated the need for extensive equipment or large sheets of material, this helped to minimise logistical challenges.
A lead alternative
Another benefit of liquid technology is it can be used as an alternative to lead, providing a more cost-effective solution that avoids the risk of theft. A liquid can be used to waterproof entire roofs or for smaller and more specific design requirements.
For example, architects responsible for the refurbishment of North Western Hall in Liverpool, specified a liquid membrane to waterproof 40 chimneys that run around the perimeter of the Grade II listed building and its slate roof.
The architects wanted to emulate a lead appearance, which saw a trial carried out on one of the chimneys. This then had to be approved by the local council before the rest of the work could begin.
The waterproofing process required a timber frame and cement board to be constructed around the top of each chimney, including the existing pots. To create a standing seam effect, timber battens were installed onto the frame prior to applying the liquid waterproofing around the structure. Combined with the seamless grey membrane, this installation process achieved the desired lead appearance.
Specification considerations
As with any roof refurbishment or renovation, it is essential that a liquid membrane is correctly specified and installed for a heritage project to ensure it performs to the required standard and that historic buildings are protected for the long term.
With such a large number of liquid roofing products now available, specifiers must ensure they thoroughly research which one is most suitable for the application. As well as complying with building regulations, and in some cases the requirements of bodies such as Historic England, there are other important considerations; such as resistance to fire of the proposed roof build-up, the compatibility of the surfaces to be waterproofed, ability to withstand substrate movement, and resistance to damage from anticipated load levels or trafficking.
Independent product accreditation is used to establish conformity and suitability, so it is advisable to research the manufacturer’s latest product certification, which is usually provided by the British Board of Agrément (BBA).
With the right specification and installation, a liquid membrane can not only meet bespoke design requirements, but also ensure a historic building remains watertight for many more years to come.
Project Focus: St. John the Baptist RC Church, Rochdale
This Grade II listed building required a comprehensive overhaul of its roof to address issues with leaks. A tapered insulation solution was specified for the first phase which saw the refurbishment of the west transept roof.
The second phase of the church roof’s overhaul saw the building’s east transept roofs refurbished, which required the use of cut-to-falls and ‘lamella’ insulation boards to fit over the barrelled roof sections. A polyester resin-based fully bonded waterproofing system was used for both these phases.
The final phase saw the refurbishment of the central dome roof. After being treated with the solvent free, epoxy-based penetrative primer, a waterproofing system was installed.
Victoria Ramwell is commercial manager from Kemper System UK