Planning a Green Roof
Green roofs are sprouting up in Toronto, and no wonder. They’re a great way to cool a building in the summer and manage water during a rain storm. Thumbs up on their aesthetic appeal too!
We caught up with Leslie Doyle of Restoration Gardens, which specializes in green roofs, to share her insights on the benefits of green roofs and her advice to homeowners who are considering this green and attractive alternative to asphalt.
GH – First, what exactly is a green or living roof?
LD – A green roof consists of a system of layers that work together to support plant life on a rooftop. They can be called green roofs, living roofs or vegetated roof assemblies. All of the green roof layers sit on top of a waterproof membrane that has been installed by a roofing contractor. The basic layers are as follows:
- Root Barrier: To protect the integrity of the membrane against aggressive roots that may grow in the system.
- Drainage: Eliminates the risk of waterlogging the system. Most drainage systems allow water to trickle through so the soil gets a chance to saturate.
- Filter Cloth: This layer is important so the drainage channels stay clear of debris and fine particles.
- Growing Media: This can be in the form of a light-weight engineered soil or a more traditional organic mix. Most roofs are built to hold about 4” of soil.
- Plants: The part that everyone gets to see!
These layers can be either laid separately or installed in a modular form. There are lots of options available!
GH – Why did you get involved in green roofs?
LD – I have a passion for the outdoors and working with my hands and was trying to look for a career that would allow me to create something that provided a lasting impression on people and the planet. Green roofs allow me to combine my previous landscaping and natural building experience. Before I started my business six years ago I found mentors, took industry classes, and did a lot of research.
GH – Why should homeowners in Toronto and the GTA consider building one?
LD – Toronto’s stormwater infrastructure is quite old and with all the new development going on, it puts increased pressure on our fragile systems. An increase of paved areas directs more water to storm drains and thus they become overwhelmed during storm events and as a result we experience flooding. Green roofs are a great way to mitigate this problem. The more permeable surfaces we create – which retain the peak flow during storms – will reduce this pressure. This is one of the reasons the City of Toronto created the green roof bylaw and started offering homeowners incentives to add green roofs on their homes.
Another benefit is the cooling effect. Green roofs help insulate a home in the summer months and as we increase the number of green surfaces, we can help reduce the overall ambient temperature of the city.
Finally, an obvious benefit would be the increase of biodiversity and aesthetically pleasing green spaces. Would you rather look out at a black surface – or a field of blooms or grasses swaying?
GH – Structurally what is required for a green roof? Are peaked roofs out of the question?
LD – The main consideration is ensuring that your house is structurally capable of the additional loading. For a basic 4” system using engineered growing media we typically request the loading to be 30psf. This loading must always be confirmed and stamped by a structural engineer. Peaked roofs are not out of the question, but require additional materials and considerations to keep the soil in place. There are lots of examples of beautiful sloped green roofs on houses.
GH – What should homeowners first consider when planning a green roof?
LD – Homeowners should consider the following:
- The purpose of the green roof. Are you doing it for aesthetic reasons? For additional insulation? To increase biodiversity? There are many reasons to install a green roof and this helps us narrow down the system we suggest.
- Their own level of involvement and interest in caring for the green roof. All green roofs require some level of maintenance. Knowing how involved you want to be in caring for your green roof will help us determine how the green roof should be built; i.e. for future access or for the level of maintenance the plants require. For example, if the homeowners like to garden and are familiar with seasonal maintenance, they may be more open to a wider diversity of species including grasses and native perennials. If they do not want to handle the maintenance, we might suggest a thin, low-growing, low-maintenance system with sedums. The depth of the system however will be determined by the structural loading.
- A budget. This will help again in determining the system that we choose and the plants we plan for. If the budget is lower we try to avoid complicated designs that require lots of seasonal maintenance and irrigation to keep the plants looking their best all year.
GH – What plant types should Torontonians consider and why?
LD – There are so many! First, I always like to have Torontonians consider native species. There are a lot of beautiful plants that are native to this region – that can survive in a shallow green roof environment – and a lot of these are drought tolerant. They also provide good sources of food for our native insects, bees and birds. After we consider native species, we consider drought tolerant species so we reduce the amount of water that is required to keep the system alive. Sedums are a type of plant you will hear every green roofer talk about. While the native sedums are more challenging to use, non-native sedums are great choices for green roofs. They come in a variety of colours and heights; they cover the roof quickly, and require very little water once established. You will also find bees swarming their blooms! But don’t worry about the bees, they don’t want you, they want the flowers.
GH – What is the typical price per square foot of green roof?
LD – This is always a hard question to answer. At Restoration Gardens we offer a variety of systems and therefore there is a HUGE range. It would be similar to asking a landscaper how much a garden costs. Factors that affect the system we suggest includes the purpose of your green roof, your aesthetics, the structural capacity of the roof, maintenance requirements, whether irrigation is to be included, the access to your roof for construction, and whether you want the roof to be accessible permanently. This is why we always start the conversation with a site visit.
GH – If homeowners are interested in learning more, how can they get in touch with you?
LD – We can be found online at www.restorationgardens.ca, or can be reached via email at email@example.com.