Living roofs or green roofs
Living roofs come in many colours, depending on the plants chosen. Foliage and flower colour change during the seasons, and they can be haven for butterflies and other wildlife.
I have been fascinated with living roofs since childhood. I never forgot how Laura Ingalls Wilder describes her father making a sod house, in her classic book "Little House on the Prairie". The roof was made with grass turves, which blended into the landscape, and it was shady and cool in summer. This form of turf roof, still used in scandinavian countries, has been adapted to other climates and is currently undergoing a revival of interest, compatible with new technologies and with contemporary lifestyle. Succulents thrive in the dry conditions of a living roof
Green or living roofs are, simply put, roofs with a layer of growing medium - soil and/or other material - sufficient to support vegetation. Living roofs are an ecological benefit in a city, bringing vegetation and wildlife into urban centers, and reducing pollution and dust levels. A New York City school testing green roof solutions
Green roofs can be built everywhere. Anyone who has observed vegetation flourishing on abandoned rooftops, dry-stone walls or gravel roadsides can testify that the right plant will find its way into the most inhospitable-looking place. Weeds colonize the roof in an abandoned chapel in Sorrento
In extensive green roofs, the layer of soil is comparatively thin, up to 20-25 cm in depth, and supports only herbaceous perennial plants and some grasses. By comparison, 'intensive' green roofs, with much greater planting depth, can support trees or large shrubs, but strictly speaking they fall under the gategory of roof gardens. Taking into account the weight of wet soil and plants, and other factors such as wind resistance and need for irrigation, a roof garden will require a much stronger building to support it, or considerable engineering work, than an extensive green roof.
Extensive green roofs are cheaper and far more adaptable than roof gardens, and are probably a more ecological solution. Some states offer incentives to companies who want to green their roofs, and there are several companies that offer green roof solutions on an industrial scale. It's possible to buy ready-made mats of plants that can be simply unrolled onto prepared roofs, many existing industrial buildings are already suitable for green roofs, with little modifications, while new industrial buildings and warehouses can have the load of a green roof easily integrated into their deisgn at a planning stage. The box frame of the roof sits on several layers of waterproofing and insulation
In central Italy, on a domestic scale, living roofs are still not standard practice. The benefits are obvious, because they reduce the ecological footprint of any existing or planned building, and integrate it into the surrounding landscape. They do however require careful planning, to consideration many variables. The load-bearing capacities of each roof, the local ecosystem, local planning regulations and building traditions, all have to be taken into account before a green roof can be designed. Once the box frame is in place, the roof is covered with a layer of expanded clay pellets, to provide drainage and a slow-release water reservoir The green roof is planted with varieties of Dianthus, Sedum, and Sempervivum placed in a planting mix over the drainage layer
A final layer of gravel tops off the planting, to hod down the lighter soil below, and provide a mulch. This protects the soil from drying out and a reduces self-sown weeds. Once established, the roof should not require additional watering, if the right balance of drought-tolerant plants is found. It takes teamwork to get everything onto the roof and in its place as the space gets tighter!
Initially upon planting, the roof still looks sparse.Over time the plants will knit together and cover the gravel mulch. This finished green roof, circa 12 metres square, is planted with over 140 plants.