What are green roofs?

Green roofs are systems that go on the top of your waterproofing membrane and typically include a root barrier, a drainage layer, growth medium and plants. Green roofs can be in the form of pre-grown modules or mats, planted or seeded on site. They can be either intensive, extensive or semi-intensive. Extensive systems are more affordable and are the easiest to accomodate on a retrofit project.

What is an extensive system?

As opposed to a much thicker and heavier intensive system, extensive green roofs have a growing media under 6” in depth, sometimes as low as 2” with vegetative mats. The fully saturated weight ranges from 10 to 50 lbs per square foot. Typical intensive systems range from 8-12” in thickness and as much as 80-120+ lbs per square foot in weight. They can accommodate frequent foot traffic and greater plant variety including trees and bushes, but require more maintenance and capital. The engineered soil media in extensive green roofs contains mostly inorganic or mineral material and is ideal for low growing ground covers. Extensive roof plants include sedums and other succulents, flowering herbs and certain grasses and mosses. Extensive systems add less load to the roof structure, are less expensive and require very low maintenance. They generally provide the same environmental benefits as intensive roofs, but are not intended to be walked on frequently or used for recreation. This is the main kind of green roofs we install because it is the most cost effective way to provide you with the benefits of having a green roof.

What benefits do green roofs have?

• Reduce runoff volume and rate of discharge by soaking up storm water that would otherwise run off, taxing city sewer systems and damaging receiving waterways;
• Lower ambient temperatures during the summer months, lowering cooling costs and helping to mitigate the so-called urban heat island effect;
• Provide habitat for wild life (and human beings)
• Increase life of roof membrane (by 200-500%) by blocking UV rays, protecting from mechanical damage and decreasing temperature fluctuation
• Decreases cooling expenses (up to 50%) and heating expenses (up to 20%)
• Reduces load on municipal sewer systems
Aesthetic and Social:
• Expands the usefulness of the building by providing additional green space
• Better looking than alternatives
• Reduces noise, improves livability, improves physical and mental health by additional exposure to nature

What plants can grow on green roofs?

Generally green roofs have low-growing, shallow-rooted sedums and ice plants. Both types are hardy succulents that are tolerant of tough weather conditions and poor soils. They are perfectly suited to deal with heat, sun, wind, drought, salt, and insects on roof tops in the urban environment. Other plant varieties can also grow, but soil design and maintenance requirements will vary.

Can I plant other plants on my roof?

Yes, and some people have vegetable gardens on their roofs, but please consult us or do some research first, because different plant varieties require different soil mix and maintenance AND some plants that have strong tap roots can damage waterproofing. If you have an existing green roof and want more plant variety, such as ornamental trees and vegetables, we recommend planting all other plants in pots and raised beds, but only after the supporting structure is checked out for additional load capacity.

Is an extensive green roof really maintenance-free?

No. Every roof needs to be checked periodically, and extensive green roofs are no different. It is important to consider maintenance with all installations, which we include for at least one year. After that we recommend that you either sign a maintenance agreement or learn to maintain your green roof yourself. We provide training on how to identify invasive weeds, disease, stray tree seedlings, etc.

Do I have to water my green roof?

After the plants are established, generally not. However, it may need to be watered during the first year of establishment if it has not rained for two weeks. If your roof was planted with drought tolerant plants, after the first year, watering should not be necessary except in extreme periods of heat and drought when you see the plants wilting substantially (Some plants go dormant during periods of extreme heat or frost). Let us know if the plants on your roof are looking diseased or brown and we will come for a check-up visit.

Do I have to worry about plants damaging the waterproofing membrane?

Sometimes, depending on circumstances. Just because plants on your green roof have tiny horizontal roots, it doesn’t mean you can’t get a surprise plant with deep strong roots looking for water however they can get it. The wind and the birds will bring seeds to your roof that will take root and should be removed. On all installations we perform we include a polyethylene root barrier between your waterproofing membrane and the green roof system, so it is highly unlikely that a weed will survive in the thin soil long enough to cause damage, but just to be sure it is a good idea to check on the weeds every month or two during spring and summer.

Green Roofs for Healthy Cities logo     USGBC logo    SBN Philadelphia logo

Remodeling and Home Design
© copyright 2014 Green Roof Works Inc. All rights reserved.