Green roof at Leeds Skelton Lake wins BALI Award
The new Leeds Skelton Lake Motorway Services at Junction 45 of the M1 sits adjacent to a 40,000m2 area of country park. To ensure the development blends in to the surrounding lakeside and to minimise the visual impact of the development, the main 5,277m2 amenity building features an over-arching, undulating green roof. The green roof is configured in eleven separate sections in a unique ‘ribbon’ pattern and the successful realisation of the design has just been recognised with a prestigious British Association of Landscape Industries award.
The wildflower roof system was delivered by green roof designers ABG Geosynthetics and their BALI affiliated installation partners Geogreen Solutions. A member of the Association's judging team visited the site at the beginning of July, and then convened with other members of the panel over 3 days in August to assess the entries and determine the winning schemes. Following a record number of entries this year, Geogreen were announced as winners in the Category of Roof Garden project with a value over £500K.
Geogreen’s work encompassed all aspects of the installation for the 11 separate ribbon areas and the judges recognised the contribution the roof design makes to enhancing the biodiversity of the site, providing a significant area of native grassland for local insect and bird species. The green roof also plays an important function as part of the development’s overall sustainable drainage strategy, absorbing rainwater and minimising surface water run-off, with as much as 95% of rainfall naturally absorbed into the vegetated surface. The vegetation, growing media and filtration fabrics within the green roof construction also helps filter dust and pollution from the air and rainfall, thus reducing the amount of chemicals and pollutants that reach the surrounding river networks.
Incorporating a green roof also significantly reduces the carbon emissions from the amenity building by allowing the heat generated to be drawn into the cool roof construction and then dissipated more readily to the environment than with traditional roof constructions. In summer months this reduces the air conditioning requirement whilst providing a level of insulation against heat loss in winter. The green roof is also very good at reducing low frequency sounds from the nearby motorway, with the extensive build up insulating up to 40dB.
The green roof build-up
The underlying structure for the extensive wildflower meadow roof is constructed from a series of interconnected glulam beams, manufactured by fixing timber boards together and forming them into the curved sections. The beams are then spanned using structural deck cassette panels of 20mm thick in 3 layers.
A Kemperol cold applied liquid membrane is applied to the timber panels to give a fully adhered, monolithic waterproofing to encapsulate the surface and preserve the deck from weathering. A 180 mm thick XPS insulation board plus a water control layer, is installed directly onto the waterproofing to complete the inverted warm roof build up.
For the base of the living roof structure, a combination of 20mm and 40mm deep Roofdrain geocomposite reservoir boards were used. The main core of the reservoir board features a grid of storage cups to attenuate rainwater and provide irrigation for planting during dry spells. Small holes in-between the cuspates allow excess rainwater to channel to the nearest drainage outlets, preventing the root growing media from becoming waterlogged and stopping water pressure build-up on the water control layer.
During the next phase of the green roof construction, a biodiverse growing media mix was deposited onto the geocomposite layer and levelled to a depth of 100mm. The material is lightweight to minimise loading on the roof structure and contains organic content to retain moisture and nutrients for growing the wildflower and sedum plants.
To complete the living roof installation a total of 4,622m2 of meadow planting was provided by Wildflower Turf, in a ratio of 20% grass / 80% flowers including a mixture of 34 different flower species. The roof turf was grown at a local nursery especially for the project and designed to thrive in the exposed conditions. The turf was supplemented with 14,200m2 of Wildflower seed to boost the density of the meadow and encourage it to spread over the wider landscape.
The green roof is subject to an annual maintenance cut in late August/early September, once flowering plants have set seed and arisings are removed from the roof to avoid nutrient build-up. Cutting the plants back to 1 to 2 inches in length ensures that re-growth and species diversity continues year on year.
Insulation, water control membrane, the green roof and irrigation system were project managed by Geogreen Solutions and a five man team worked to complete the install. This was Geogreen’s largest install programme to date and in total 5,000m2 of green roof sedum and wildflower matting, over 6,000m2 of insulation board, geocomposite drainage and waterproof membrane, 28 tonnes of 20mm pea gravel for fire break borders and 12 arctic loads of 1m3 growing media bags were delivered and installed for the new services.
The National Landscape Awards event and winners’ presentations are being held at the JW Marriott, Grosvenor House Park Lane Hotel on 3 December.