A green roof is a layer of vegetation that entirely or partially covers a building rooftop, and compensates for the amount of vegetation removed from the ground in constructing the building. A waterproof membrane separates the vegetation from the rooftop, protecting it from damage. In fact, green roofs can significantly extend the lifespan of roofs not only by reducing stormwater runoff, but also by shielding against wind, frost, UV rays and debris. Further benefit includes temperature regulation of your home, maintaining warmth in winter and cooling in the summer.
A low-growing, dense, drought resistant vegetation style – categorized as “intensive” – is most common amongst single-family or multifamily residential buildings. Alternately, garden roofs – categorized as “extensive” – are composed of trees, flowers, bushes, shrubs and other taller, heavier vegetation.
- Familiarize yourself with municipal regulations regarding height restrictions in your area, which could affect your decision in choosing between an intensive or extensive roof.
- Arrange for an analysis of your roof by a structural engineer. It is important to know the load capacity and restrictions of your roof. Additionally, a structural engineer can provide design recommendations for roof reinforcement if necessary.
It is recommended to hire a professional roofing contractor or landscape contractor trained in green roof installation.
The green roof is installed in layers:
- A waterproof membrane that will prevent water damage to your roof.
- An impenetrable root barrier, such as concrete, asphalt, or cellular glass, to prevent plants from working their roots into your roof.
- A drainage layer, usually gravel, to allow excess water to drain into eaves troughs.
- Filter fabric, usually polyester or polypropylene, to prevent soil from clogging the gravel and to help hold the vegetation layer in place.
- Growing medium, such as soil (e.g. a mixture of clay, sand, topsoil, and humus) or an engineered substrate, with a depth of at least 3″.
- A layer of vegetation that is comprised of native plants, acclimatized to survive in all seasons. You can find a list of plants native to Atlantic Canada here.
- Biodegradable wind barrier – prevents wind erosion of the soil and is especially important during early plant establishment. A wind barrier can include compost, mulch, or straw.
- Drip irrigation system – simplifies watering and is more efficient than using a hose. This system keeps plants moist and helps them to establish during early growth; it can be removed later, if desired.
Maintenance should be considered in the design process. Light annual maintenance of the green roof will ensure optimal performance.
- Gutters and drains should be cleared, and debris should be removed.
- Extensive roofs may involve weeding up to three times per year, while intensive roofs will require the same level of maintenance as regular gardens.
- Dead vegetation should be replaced once it has surpassed 5% of total installed vegetation.