This crassula is perfect to use for a green roof (Photo by Jane Gates)
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With all the new interest in ecological building, the green roof is coming into its own. A green roof is a method of building insulated roofing out of living materials.
Green roof technology has come a long way from its simple beginnings centuries ago. The concept is simply that the soil or medium in which shallow-rooted plants grow can be planted like flat ‘tiles’ on the roof of a structure. This creates an excellent form of insulation which is self-renewing as the low- growing plant material forms a living surface.
Parts needed are water membranes, forms for planting, irrigation and drainage systems, a planting medium and plants. Various styles of structural containment forms can be built or bought in kit form. Irrigation can be set up over or under the plants themselves, the moisture creating additional insulation. An efficient water-proof layer is laid on the surface of the building under the planting area before the planting tiles, irrigation, and drainage systems are put in place. No water should get through the waterproof membrane to the structure below. This same concept is also being used to create living walls or vertical gardens.
Green roofs have been used in one form or another over history, but the new form of green roof is highly efficient and designed to avoid rot, pests and to keep maintenance minimal.
Grass is popular for planting on green roofs since it is clean-looking and does well in many climates. In very hot and dry climates low-growing succulents like sedums are more successful as they dry out less readily, retain more of the water in the leaves (even better for insulation) and can be more resistant to hot sun. Many of these succulent plants are colorful in leaf and flower alike.
Roofing has to be built carefully and you might want to study the construction before trying it yourself. Or call in a professional. Either way, it is important that weight is well distributed and the container system is well integrated with irrigation and drainage systems. Smaller roofs are easiest to turn into green roofs and roofs with steep angles can be problematic. Look into building a green roof in the garden on sheds, enclosed patios, or outdoor rooms for an ecological way to extend your garden while providing cooling for the space beneath.
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