Putting a biodiverse ‘living’ roof on top of a building transforms a flat elevated landscape devoid of life into a vibrant, flower-rich habitat buzzing with wildlife.
A ‘green roof’ or ‘living roof’ is a roof covered by vegetation.
Biodiverse roofs can be retro-fitted onto existing buildings or incorporated into new builds.
Living roofs use a thin growing medium on top of various layers that protect the underlying building or structure. The waterproofing layer and the root barrier are particularly important.
Low-nutrient soils provide an ideal growing medium for the wildflowers and plants that attract pollinators and other wildlife.
Benefits of Living Roofs
In addition to the benefits to pollinators and other native wildlife, living roofs can provide a host of other benefits, including:
- Improving building insulation and cooling.
- Providing drainage.
- Reducing CO2 emissions.
- Increasing the value of buildings and developments.
- Increasing the lifespan of roofs.
- Positive benefits to health and wellbeing.
- Improving air quality.
- Noise reduction.
- Enhancement of the Environment.
Biodiverse Living Roof Plant Species Mixes
Most off-the-shelf ‘green roof’ products consist solely of Sedum plant species. While such mixes will provide some benefit, including a broader range of native wildflowers (including up to 30% Sedum) will provide far more value to pollinators and other wildlife.
The following biodiverse living roof plant species mixes have been designed specifically for use in Jersey.
Careful consideration has been given to the potential impact on wild plant populations when developing these mixes and associated guidance.
Biodiverse Living Roof Plant Species Suitable For Jersey’s Urban Environments
The following green roof species mix is suitable for use within Jersey’s urban environment as defined by the ‘built-up area boundary’ of the bridging island plan.
Perennial Wildflowers
Yarrow Achillea millefolium
Common Knapweed Centaurea nigra
Wild Carrot Daucus carota
Oxeye Daisy Leucanthemum vulgare
Bird’s-foot Trefoil Lotus corniculatus
Self Heal Prunella vulgaris
Red Campion Silene dioica
Common Vetch Vicia sativa
Biting Stonecrop Sedum acre
English Stonecrop Sedum anglicum
Ribwort Plantain Plantago lanceolata
Annual Wildflowers
Cornflower Centaurea cyanus
Corn marigold Glebionis segetum
Common poppy Papaver rhoeas
Grasses
Common Bent Agrostis capillaris
Crested Dogstail Cyanosurus cristatus
Red Fescue Festuca rubra
Biodiverse Living Roof Plant Species Suitable For Jersey’s Wider Countryside
The following green roof species mix is suitable for use within Jersey’s wider countryside as defined by the ‘green zone’ and ‘green backdrop zone’ boundaries of the bridging island plan.
Perennial Wildflowers
Yarrow Achillea millefolium
Common Knapweed Centaurea nigra
Wild Carrot Daucus carota
Oxeye Daisy Leucanthemum vulgare
Bird’s-foot Trefoil Lotus corniculatus
Self Heal Prunella vulgaris
Red Campion Silene dioica
Common Vetch Vicia sativa
Biting Stonecrop Sedum acre
English Stonecrop Sedum anglicum
Ribwort Plantain Plantago lanceolata
Grasses
Common Bent Agrostis capillaris
Crested Dogstail Cyanosurus cristatus
Red Fescue Festuca rubra
Properties Adjacent to Sites of Special (Ecological) Interest
Please note that we do not recommend that the species mixes detailed above are used within 400 metres of a designated or proposed Site of Special (Ecological) Interest (SSI).
We recommend an approach based on natural colonisation or assisted colonisation using seeds harvested from the local area for sites within 400m of an SSI. Please bear in mind that it is against the law the collect seeds within an SSI without first obtaining a licence from the Government of Jersey.
Seeding and Planting
Other than natural colonisation, wildflowers are established on roofs using two main methods:
Seeding
The most cost-effective option. However, wildflower seeds can take some time to germinate and become established at roof level due to the extra stresses placed on the habitat, such as drought and wind. Including fast-germinating annual species will provide important resources for insects in the first year of establishment.
Plug Planting
Planting plug plants in conjunction with sowing seeds can help speed up the establishment of a living roof and provides resources for invertebrates during the first few years whilst the seeded plants are becoming established. Plug planting also gives greater control over initial plant coverage.
Designing a Biodiverse Living Roof
Important considerations when designing a living roof include:
- The weight (dead load capacity) that the roof will exert on to the building.
- The placement of drainage outlets enabling excess water to flow off the roof.
- Waterproofing.
- Root barriers.
- Substrate type and depth.
Maximising Biodiversity
Additional habitat features can maximise the potential of biodiverse living roofs to support invertebrates and other wildlife. Always consider the additional loading implications when adding habitat features to a roof.
Vegetation left uncut through the winter will provide over-wintering opportunities for a variety of invertebrates in seed heads, hollow stalks and stems.
Dry areas of open bare ground, stones, bricks, rocks and gravel can warm up quickly and will benefit a wide variety of species, including butterflies, bees, wasps, beetles and spiders.
Log piles and deadwood piles provide shelter and nesting sites for a wide range of invertebrates.
Bee banks provide nesting habitat for solitary bees and wasps and can easily be created by shaping sand into a mound. Bee banks should ideally be South facing to receive the most sunshine throughout the day. Bee banks should not be higher than the parapet wall (the barrier at the roof’s edge).
Water-bodies and wet areas provide essential habitat and resources for many species. They can be provided in the form of ponds, undulations or simply by placing a shallow plastic container on the roof.
Bug hotels and habitat walls provide places for invertebrates to shelter, over-winter and nest. They can be purchased or made using items such as pallets, bamboo canes, logs and recycled building materials.
Living Roof Management and Maintenance
Biodiverse living roofs require little ongoing management and maintenance. This is largely due to the exposed, low nutrient, shallow substrates and root barriers that slow ecological succession processes.
Living roofs should receive two maintenance visits each year to undertake essential tasks such as:
- Weeding.
- Mowing or cutting.
- Regular inspections of infrastructure such as drainage outlets.
Ecological Surveys and Monitoring
Monitoring is essential to determine which species are using the roof. The information gathered can be used to inform future management and to study how roof design and management influence biodiversity.
