Can you put a green roof on an existing roof?

Despite the weight of living roofs, many are discovering that they can be installed in existing buildings much more easily than previously thought. Whether the structure is a historic landmark or a more recent commercial structure, there's a good chance that a green roof can be installed on the existing building. Due to weight limitations in most existing structures, extensive green roofs are more suitable for modernization. Intensive green roofs offer more options for a wider selection of plants, but they generally weigh much more than extensive roofs.

Usually, a green roof system behaves like a hat on a traditional roof. Typical roof membranes, roof drains and conical insulation are part of an ecological roofing system.

Green roofs can be installed using a series of planting trays or creating a bordered garden area on the roof.

These instructions are for installing a landscaped area on a flat surface using a multi-layer waterproof protective barrier between the floor and the roof covering, which could be plywood, for example. The various layers, easily available in landscapers or stores, will not only prevent water from penetrating the terrace and rotting, but will also prevent roots from reaching the terrace and weakening or rotting it.

Some of the most successful renovations, adding a green roof to an existing building, have been done on older concrete or masonry structures that support loads. They can be installed on low-sloped roofs with an elevation of up to three feet for every 12 feet of length without stabilizing them. Under the right conditions, I would say yes, it's possible to make the transition from a metal roof to a green roof, but it's not ideal and you're likely to face some challenges. As you would with any garden, early spring or early fall is the best time to install a roof garden so that plants have time to get established before the extremes of summer or winter.

The trays can be planted with the same plants as on a roof without pots or they can be purchased already grown commercially in a nursery. Green roofs generally need to be weeded two or three times a year to prevent overgrown vegetation from clogging drains. The roof itself is in very good condition, but I would like to transform it into a green roof, hopefully as a DIY project. Frame the sides of the roof with mesh guards for gutters, wood or other edges that allow drainage to keep soil in place.

Plants that stay green all year round are good options because the roof will stay green in winter, when many plants are dormant. With some creative solutions available on the market, modernizing an existing building to adapt it to an ecological roofing system may be a viable option. Be sure to create a roof that adapts to the width and length of the trays without leaving gaps. Your vegetated roof may not look vibrant during the harsh winter months, but if you're growing perennials that can withstand that climate, they should return in spring.

A green roof can add up to 30 pounds of load per square foot, so consult a structural engineer to see if you need to add reinforcements to your roof.