Victoria Ramwell from Kemper System, the cold-applied liquid waterproofing specialist, discusses liquid best practice for green roof specification.
Liquid waterproofing systems provide one of the most long-term and cost-effective solutions for any green roof project. Correctly installed and maintained, they can provide a durable and robust solution, often in excess of 20 years.
Because of their seamless nature, root resistant grades of liquid applied waterproofing systems are ideally suited for use in green roofs without the need for an additional root resistant layer.
Suitable for both warm and inverted roof installations, liquid waterproofing systems should be British Board of Agrément (BBA) Certified for green roof applications, with the installer ensuring the correct grade of product is being applied.
Design stage considerations
Plants within the green roof must be agreed from the outset, as the roof will need to be designed accordingly. Wildflower meadows, for example, are a popular choice for large roof surfaces, but they need plenty of moisture, which means designing the roof to accommodate the load and providing a deeper reservoir core. Alpine planting however, needs much less water to thrive so this will have less of an effect on the roof’s load bearing requirements.
Is it also vital that location and prevailing climatic conditions are considered as these govern the amount of light, heat, shade and moisture the roof will receive.
A watertight solution
The effectiveness of the waterproofing membrane between the roof substrate and the green roof system is the most important element of the specification. The membrane should be flexible enough to manage with any post-build settlement, durable enough to cope with the planting’s load bearing requirements and have a sufficiently long service life to make the green roof viable.
A common green roof design would typically consist of an inverted warm roof build-up with the waterproofing system applied to the roof substrate, followed by the insulation, and then the green roof elements. This can add an extra layer of protection for the waterproofing membrane as it is cushioned underneath the insulation.
However, a liquid waterproofing solution such as Kemperol V210 or Kemperol 2K-PUR can be cold applied either below or above the insulation, depending on the type of insulation used. These systems are FLL certified as root resistant, so there is no risk of damage even as plants mature.
Liquids in the spotlight
One recent green roof project saw Kemper System’s Kemperol V210M cold-applied liquid membrane used at the new, £64M Leeds Skelton Lake Motorway Services.
Located at Junction 45 of the M1, the service station is adjacent to Skelton Lake – a 40,000 sq. m area of ecologically diverse country park, two miles south east of Leeds city centre.
The new building includes a food court, shops, businesses as well as leisure and community facilities within attractive and relaxing surroundings.
To minimise the visual impact of the development on the natural landscape and local wildlife, the main amenity building features a 5,277 sq. m over-sailing, undulating green roof.
The roof is configured in a unique ‘ribbon’ pattern with eleven separate sections, adjoining a new 100 room Ramada hotel. The extensive wildflower meadow green roof – designed by ABG Geosynthetics and installed by Geogreen Solutions – forms the main feature of the building.
The roof structure is made up of a series of interconnected glulam beams, constructed from layers of timber boards glued together. The curved beams are spanned using structural deck cassette panels of 20mm thickness, in three layers.
Kemper System’s Kemperol V210M was installed by contractors, Cawston Specialist Roofing, to the timber panels. The cold-applied resin was poured onto the roof and a reinforcement fleece was laid directly into the wet resin, immediately followed by more resin to completely saturate the fleece.
Once cured, the resin formed a seamless, elastomeric waterproof membrane that cannot delaminate, is UV stable and bonds directly to the substrate. The fully adhered, monolithic waterproofing is root resistant and encapsulates the surface to preserve the timber deck and protect it from weathering.
Contractors then installed 180mm Polyfoam XPS (extruded polystyrene) insulation board and a water flow reducing control layer directly onto the waterproofing to complete the inverted warm roof build-up. The insulation was ballasted during the install to prevent uplift prior to the green roof installation.
To complete the roof structure, a total of 4,622 sq. m of meadow planting was provided by Wildflower Turf Ltd, which included 34 different wildflower species. The turf was locally grown to be compatible with the local region, enhancing the biodiversity and ecological value of the area, while providing native grassland for birds and insects.
The project has been shortlisted in the Liquid Roofing and Waterproofing Association (LRWA) Awards 2022 in the Liquid Roofing Project of the Year in a Buried Application category.
Stephen Humberstone at ABG said: “The green roof plays an important function as part of the site’s overall sustainable drainage strategy, by absorbing rainwater and minimising surface water run-off. As much as 95 per cent of rainfall is captured within the green roof build-up to minimise the risk of localised flooding.
“We needed a reliable and versatile waterproofing solution to ensure we could specify a warm roof build-up which would offer durability. The ease of application was also a deciding factor due to the sloping ribbon design of the building.”