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FAQ



Below are some of the more commonly asked questions. If you have a questions that you don't see below please feel free to contact us at info@greenrooftechnology.com and we may even add it to the list!

How much does a green roof cost?

Counting all the material above the waterproofing, the cost of a green roof on a flat roof typically starts around $15 a square foot. This covers a basic 4” system with sedums and hearty herbs. Growing media depth, desired water storage, and plant material, and slope determine the increase in cost from there. Green roofs generally become up to 50% cheaper by the square foot as the square footage exceeds 10,000 feet.

Can you put a green roof on an existing building?

Yes. Many of our green roof projects involve existing buildings. The building must first be check by a structural engineer to determine the weight bearing capacity. Waterproofing must be in excellent condition, typically no older than 5 years, though having a green roof installed when you need to redo your roof is the best option. Having the waterproofing replaced right before the green roof is installed ensures maximum protection for the waterproofing and a more compatible system.  This is also the best time to set up a leak detection system.

What is the difference between a modular system and a traditional built up system?

Most modular systems basically function as planters. They are laid directly on the waterproofing membrane and can cause leaks if placed on debris or moved. Waterproofing damage from UV rays and roots can also be a problem. There are some with open sides to let the roots spread out.  These are better than the above mentioned modular planters however drainage is not as good as a traditional system and they are still typically more expensive. The advantage is that you can have instant green on your roof.  However, this can also be achieved on a traditional green roof through the use of vegetated mats similar to sod mats.

A traditional built up system has many names such as loose-laid, wall to wall, and continuous system. Whatever the name, it is a layered system that covers a defined area and is assembled on the roof. This system offers superior UV, debris, elements, and root protection. Drainage, water retention, and plant health are typically superior as well.

Can I have a green roof on my sloped roof?

Yes. There are many different ways to set up growing media and drainage supports to keep the green roof from moving. In terms of cost however the price will increase with the steepness of the slope.

Are there incentive programs or grants that can help with the cost?

Yes. We have worked with many groups that have found funding for their green roof through city incentive programs, government grants, and organization grants. Check your local environmental groups, municipalities, and federal grant websites for more info.

Can I grow food on my roof?

Yes. You can grow hearty drought tolerant herbs like rosemary, thyme, and chives on a green roof very successfully.

Traditional crops such as tomatoes and peppers require a deeper growing media depth with lots of irrigation and maintenance. Some of the more tender crops may find the location too harsh and the growing media unsuitable. If you are in an urban area be sure to check to see if the plants and parts you want to eat are air pollution sinks. Plants and or sections of the plant absorb and store pollutants differently and at different levels.

Your best bet would be to have a raised planter system for traditional crops. This requires less irrigation, maintenance, and the rich organic soils that the crops love is kept separate from the green roof and or roof drains. Rich organic soil is horrible for green roofs mainly because of the multitude of drainage problems they cause with a green roof system.

Can I use potting soil or any soil from the ground on a green roof?

NO! This is recipe for disaster. Growing media is used not because it sounds cool or is an accessory designed by manufacturers. Growing media is specially mixed and selected light weight materials composed mainly of mineral components with very little organic matter that has been sterilized. This allows for proper water retention and drainage which is key for a green roof's success. Low organic matter is good because the plants that grow normally in a green roof environment don't need lots of nutrients. In some cases too much nutrients can actually damage the green roof plants.  More importantly, the fine particles created from organic material breaking down can clog the drainage systems of the green roof causing it to fail.

What is the maintenance involved in a green roof?

That depends on the green roof. A typical extensive green roof composed of a 4 inch system with mixed sedums needs water sparingly for the first year and weeding every few months. The following year it shouldn't need any water and will only need to be weeded 3 to 4 times a year. After the second year it should only need to be weeded twice a year. Fertilize only once a year.

More garden like green roofs need more maintenance and will need to be maintained similar to their ground level counterparts. In general, avoid using mulch and similar materials that can break down.

Do I need to water my green roof?

During the first year, regardless of plants or system used, it is recommended that you water to aid establishment. In general, for a green roof to be “green” in terms of being ecologically friendly it shouldn't need to be watered after the first year. Irrigation wastes water and energy, both are what the green roof should be conserving.

How long will my roof last with a green roof?

A properly installed and maintained green roof should extend the life of the roof 2-3 times its normal life. 30 to 50 years is not an unusual lifespan for green roofs in Europe.

How do I check for a leak if I already have a green roof?

To avoid a needle in a haystack search the best thing that you can do for yourself and your green roof is to have your waterproofing checked for leaks prior to installation and to have a leak detection system installed.

Electro Field Vector Mapping (EFVM) is very accurate and able to find leaks that traditional flood testing wouldn't. EFVM testing can also be done anytime after the green roof is installed and is often cheaper than the cost of a waterproofing manufacturer's warranty. Roughly 80% of the green roofs we have specified contain this system.


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"This award winning project, completed in 2000, was among the first modern green roofs in the United States... Jorg's assistance was essential in their success."

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