How to Maintain a Green Roof? [Best Practices to Follow]

Green roofs are vegetated roof systems that absorb rainwater and help to reduce the heat island effect. They also provide a habitat for local wildlife and improve a building’s overall aesthetics.

Despite these benefits, green roofs like any other roof need regular maintenance to ensure that they last for a long time. Because if not properly maintained, green roofs can do more harm than good for a building.

An improperly or insufficiently maintained green roof can result in costly repairs as well as safety hazards for the surrounding environment.

Therefore, it’s important for building owners to properly maintain their green roofs. Fortunately, you don’t need to reinvent the wheel when it comes to maintaining green roofs.

There are already tested and proven best practices that you can follow to ensure the longevity of your green roof. In this article, we’ll discuss some of those best practices as well as how to detect and prevent certain water leakage issues on green roofs.

What type of maintenance would a green roof need?

All roofs require regular maintenance. However, green roofs need to be maintained carefully than traditional roofs. It is because of the different components that make up green roofs.

Typical green roof maintenance should include performing regular inspections to identify any potential problems, clearing debris from the roof, checking that the drainage system is working properly, and maintaining or replacing plants.

Obviously, there are very different types of green roofs that differ in their maintenance requirements. But for the most part, we can group them into three categories: intensive, semi-intensive, and extensive green roofs.

Maintenance for different types of green roofs

Intensive green roofs are roofs that have a deeper soil depth and larger plants. While semi-intensive and extensive green roofs are more shallow soil depth and less plant material.

Therefore, having an intensive roof will require more time and budget for maintenance than semi-intensive or extensive roofs.

Most intensive green roofs will have trees and larger-sized plant material and may also require their owner to get help from an arborist or landscaper.

Because depending on the selected plant type maintenance requirements can greatly vary. Also, some plant types require frequent irrigation while others will survive with little to no irrigation at all.

Maintenance after the initial installation

No matter what plants you choose to plant on your green roof, you will need to regularly water and fertilize them until they are established.

Since the initial installation is the most crucial time for your green roof, it is always a good idea to hire a professional who has experience designing and installing such roofs.

During this period, you should regularly inspect your green roof for plant growth, soil moisture, and drainage.

After several months, when your green roof is fully established you can follow the recommendations of your green roof professional for regular maintenance.

How often you should maintain your green roof?

After your initial installation, you should perform regular inspections. You can do the maintenance yourself or hire a professional to inspect the roof for you.

Regular inspections will help monitor the health of your green roof and identify any potential problems, which can then be addressed before they become bigger issues.

The frequency of regular inspections varies depending on the type of green roof that you have installed, its location (climate conditions), plant types selected for the roof, and other factors.

In general, a green roof should be visually inspected once a month and immediately after a storm event. A visual inspection will provide a quick overview of the overall health and condition of your green roof.

In addition to visual inspections, you should also perform regular maintenance tasks. This includes regular weeding and cleaning of the roof, checking that the drainage system is working properly. Also, it’s important to check for any signs of pest infestation, which can occur if vegetation is not healthy.

What types of problems can green roofs have?

There are different types of problems that can occur on a green roof. Some of them are related to the selected vegetation and soil types while others are related to the design, mechanical failures, and water leakage.

But leaking is probably the biggest problem that can occur with a green roof. Because it can damage the structural integrity of the roof and cause mold and other moisture-related issues.

Why do Green Roofs Leak Water?

Green roofs can often face water leakage issues due to the following reasons: 

Poor waterproofing

All roofs need to be waterproofed carefully and green roofs are no exception. In any case, you will need to work with a competent waterproofing contractor to verify that your roof is watertight.

Because your roof membrane must be thoroughly inspected before installing a green roof to determine whether it needs to be repaired or replaced.

Most green roof manufacturers will not provide a warranty for their green roofs if they are installed on a membrane that is not new and/or has not been verified by a trusted contractor as watertight.

Therefore, the best time to install a green roof is immediately after you replace your roof membrane. You shouldn’t install a green roof if you didn’t verify that your roof membrane is watertight.

Another good reason for fixing or replacing the roof membrane before a green roof installation is a need for elevating the roof’s waterproofing layer.

Typically, a roofing contractor would waterproof up a wall adjoining a roof to 200 mm (8 in.) above the roof surface, followed by metal counter-flashing to prevent moisture from melting snow from seeping behind the façade.

When installing a green roof this distance should instead be measured from the green roof surface (i.e. growing media surface). For example, if the green roof has a 150-mm (6-in.) deep growing media, the waterproofing should extend at least 350 mm (14 in.) up the wall.

The parapet wall should be built at least 100 mm (4 in.) above the green roof surface, with the waterproofing membrane wrapping around the top and being topped with metal flashing.

Therefore, if you plan to install a green roof to your existing building, you must make sure the waterproofing membrane extends high enough to cover the additional height that the green roof creates.

Also, water leaks are more likely in difficult-to-waterproof areas, such as horizontal-vertical surface intersections around parapets, equipment, or penetrations (e.g., for drains and pipes).

Therefore, green roofs should be installed at least 300 mm away from these elements to make future membrane repairs easier.

Concrete pavers are commonly used on green roofs to create access paths. However, they should never sit directly on the roof membrane. Otherwise, the foot traffic can permanently damage the membrane.

If the membrane contains bitumen or other organic material, it must be kept separate from the plant layer to prevent root penetration and micro-organism activity.

There are newer membranes on the market for green roof applications that include a root-deterring chemical or metal foil between membrane layers and at junction/seam lines to prevent root damage. These products are more expensive than traditional roofing membranes, but they are well worth the extra cost.

Also, the membrane’s chemical composition must be compatible with the system components with which it will come into direct contact.

The fact that the green roof system entirely covers the waterproofing membrane can make maintenance and visual inspections difficult. Leaks at joints, penetrations, and flashings can occur owing to poor installation rather than material failure.

Poor Drainage

Roof drainage is critical, especially when vegetation is present. Ponding water on a traditional roof will dry up quickly on sunny days, but it will remain moist on a green roof.

If the drainage system is not properly designed or installed, water may pool on top of the roof.

Prolonged ponding water may reduce the service life of the membrane, so effective drainage is critical. To encourage water flow and avoid drainage barriers, roof drains should be installed at a slightly lower level than the roof membrane.

Also, drainages should have slotted coverings to catch leaves and block gravels. If possible, the roof should be constructed as separate waterproofing zones. Separating the drainage areas makes it easier to find potential leaks in the future.

Improper Plantation

Green roofs are vegetated roofs, and the vegetation is essential for absorbing the amount of water that flows through the roof.

If the selected green roof lacks sufficient vegetation or the plant selection is incorrect, it may not soak up enough water during a storm event.

There are many factors that affect a plant’s ability to absorb water, including its species, size, and root system. In the first two years of establishment, plant survival on a green roof is directly related to the amount of maintenance time and budget allocated.

To ensure the plants’ ability to adapt and flourish, it is critical to know where they were previously grown and if the growing conditions were equivalent to those on the roof. Therefore, it is important to research the plant species closely in order to establish the proper growing conditions.

Construction & Installation Issues

Installing a green roof requires the knowledge of various trades including waterproofing, drainage, insulation layers. If it is not incorrectly, it may lead to drainage issues and other problems.

When you hire a contractor to install a green roof, it is important to make sure the company has experience in the field. Ideally, you should work with a single company that can handle the entire project. It would be great if the company can handle re-roofing, planting, and establishment.

If you hire multiple contractors for different parts of the project, make sure to coordinate their work to avoid scheduling conflicts and damage claims between the various trades. 

Mechanical Damage

Mechanical damage is a reason for leakage and is typically caused by moving equipment, foot traffic, and strong winds.

When you plan your roofing project, you should plan with proper access paths to avoid foot on your green roof.

There should be a path to allow pedestrians to walk across the green roof without causing damage. Also, the maintenance team and occupants should be encouraged to use this path when they are on the roof.

Strong winds can damage vegetation by ripping out vegetation and moving the growth media through erosion.

To protect against strong winds, you can install a wind barrier behind the parapet. If the green roof is planted with delicate vegetation, it will be susceptible to mechanical damage.

Also, snowfall and freezing temperatures can damage vegetation. Therefore, green roofs should be protected from high winds and freezing temperatures during winter seasons.

Poor Maintenance

Green roofs are also susceptible to problems due to a lack of regular maintenance.

For example, many building owners fail to inspect their green roofs regularly for any signs of damage or wear and they only discover leaks and water damage when it’s too late to fix them.

Although the green roof will absorb a large amount of rain, adequate roof drainage is essential.

If the drainage layer is too thin or the routes to the roof drain become clogged, the membrane may leak due to constant contact with water or a wet medium.

On a roof with a slope more than 20 degrees, the green roof installer must ensure that the sod or plant layer does not slip or sag due to its own weight, particularly when wet.

This can be avoided by using horizontal strapping, either under the membrane or loosely laid on top, made of wood, plastic, or metal. Some green roof manufacturing companies have created support grid systems for green roofs, particularly for this application.

Lack of vegetated free zones around drains or scuppers

A lack of vegetated free zones around drains, scuppers, and roof penetrations will reduce the ability of water to flow away from roof drains. In turn, this can lead to pooling and leakage issues around roof drains.

By laying gravel directly around the perimeter of a roof drain, you can keep these zones from clogging up with plants.

To prevent blockage by overgrown plants and dead biomass, keep the plants at least 300 mm (12 in.) away from roof drains. On top of a drainage mat, fill this non-vegetated border with washed round river stones.

Emergency overflows, such as scupper drains, should be constructed on roofs with a minimal structural load-bearing capacity to divert excess water off the roof if the main drains become clogged.

How to Prevent Water Leakage Issues on Green Roofs?

There are several steps building owners can take to prevent water leakage issues on green roofs. Here are some of them with no particular order of importance:

Regular Inspection & Maintenance

Regular inspections and maintenance of the green roof is essential to avoid any potential issues.

By conducting regular inspection and monitoring, you will be able to detect possible signs of water leakage such as:

  • Blistered/cracked membrane or growing medium
  • Loss of vegetation due to mechanical damage or lack of adequate irrigation
  • Browning/dying vegetation due to lack of irrigation or root damage
  • Staining on parapets, walls, and ceilings may indicate ponding water around the roof drain system.

These are just some signs you should be looking for when conducting your regular inspections. By being proactive with your maintenance plan, you will save yourself a lot of headaches and money in the future.

Building owners need to make sure their roof’s drainage system is in good working order, there aren’t any damages that have been caused by snowfall or strong winds, and they should regularly inspect growth media for compaction.

Plant maintenance, as well as waterproofing membrane upkeep, are also required. Plant maintenance will range from monthly checks to check for weeds or damage, to weekly visits for irrigation, pruning, and replanting, depending on the extent of the green roof.

If you plan to hire a green roof contractor to take care of your green roofs, make sure they will provide you with a maintenance plan and schedule. This way you can know what they will be doing for each visit and how often it should occur.

Use the Right Growing Media

Growing media is responsible for not only holding down the vegetation but also absorbing water and providing a suitable substrate.

Therefore, projects should choose the right growing media for each green roof based on the plant types, drainage rate, and soil stability.

When choosing a growing media, make sure it can hold up well against compaction and erosion, has an adequate drainage rate to prevent water accumulation, is compatible with the chosen vegetation.

Inspect your roof’s vegetation

You should regularly check the vegetation on your green roofs. If your plants appear damaged or are not growing properly, your growth media may be too compacted and not draining properly. This may lead to drainage issues and eventually water leakage on green roofs.

Install a Sediment Control System

A sediment control system can be installed underneath your green roof to catch sediment and slow down water runoff.

This will help to prevent clogging of your roof’s drainage system and eventual water leakage. There are a variety of different types of sediment control systems that can be used, so it is important to choose the right one for your specific project.

Install a Root Control System

A root control system can help green roofs avoid water leakage. In other words, it helps hold down your roof’s sedimentary layers and drainage material while still allowing for healthy vegetation and root growth.

Use perlite in growing media

Perlite is a type of volcanic glass that is naturally porous and lightweight. It can help improve your green roofs’ water retention soil structure by expanding up to 20 times its original size when it gets wet.

Perlite also promotes healthy root growth and reduces potential weed problems by allowing air circulation within the growing media. It can aid in the prevention of compaction problems, which can lead to drainage issues and eventually damage your green roof’s sedimentary layers and drainage material.

Use a Drip Emitter System

Drip emitters deliver water to the vegetation slowly, so they are a more efficient way of watering your green roofs.

This helps prevent runoff and reduces potential irrigation issues by not over-irrigating or under-watering your roof’s vegetation. This is also more environmentally friendly since you will be using less water for irrigation purposes with a drip emitter system.

Ensure Proper Drainage System & Vegetation Placement

The vegetation and drainage systems on green roofs should be designed with water runoff efficiency in mind.

You want to make sure that your roof’s sedimentary layers do not get damaged easily by heavy rainfall or snowfall so you need to ensure proper plant placement as well as a strong root system. You also need to make sure the growth media and the root system are not too compacted.

Use a Durable Green Roof Installation System

When installing a green roof, you want to use a system that is durable and can withstand the weight of the vegetation and growing media.

This will help reduce the chances of water leakage caused by damage to your roof’s drainage system or substrate layers. Make sure to ask your contractor what type of installation system they plan on using for your project.

Conduct Electric Field Vector Mapping (EFVM) Testing

EFVM®, or electric field vector mapping, is a sort of non-destructive testing that is used to find a crack or void in a waterproofing membrane.

This test is aligned with the requirements of ASTM D8231-19 (Standard Practice for the Use of a Low Voltage Electronic Scanning System for Detecting and Locating Breaches in Roofing and Waterproof Membranes).

The testing procedure is quite simple. The tester creates an electrical potential between a non-conductive membrane and a grounded conductive deck or substrate by using a low-voltage electrical current.

If there is a leak, the electric current will follow the path of least resistance to find the crack or void.

In turn, this will indicate where the crack or void is located. EFMV testing is particularly useful before the roof is sealed or a green roof is planted. Because it can pinpoint smaller pinhole leaks that might otherwise go undetected.

Conduct Infrared Thermography Testing

Infrared thermography testing is a very useful tool that can help building owners detect and prevent water leakage issues on green roofs.

With infrared thermography testing, a camera captures the heat emitted by objects. It can detect changes in temperature around the roof that could indicate where there are potential leaks.

If there is a leak existing in the waterproof membrane, water can enter the roof system through the waterproof membrane and saturate underlying layers. Since wet roofs take longer to cool down than dry roofs, the leaky membrane will be cooler than the rest of the roofing system.

Conduct Electrical Impedance Testing

Electrical impedance testing is a non-destructive testing method that can be used to detect and map water leakage issues on green roofs. It involves an electronic charge being applied to a membrane.

If there is a leak, the electrical impedance will be lower in that area since water has entered into or short-circuited the membrane. With this type of testing, you can get a clear visual representation of where there are any leaks on your roof.

Nuclear Moisture Testing

Nuclear moisture testing is an advanced water leakage issue detection method that can help building owners detect and prevent possible leaks in green roofs. This type of test involves detecting hydrogen ions in a roof system since they often signal the water’s existence.

With this testing, a nuclear gauge is used to detect water by measuring the speed of neutrons. When assessing data from this highly sensitive nuclear detection approach, the original hydrogen level of a roof must be taken into account as well.

Hydrogen measurements for dry materials are obtained by the use of minimally invasive testing procedures. After establishing dry material baselines, increased hydrogen counts indicate roof system moisture degradation.

Invest in an intensive green roof system

One of the most important objectives of using green roof systems is to slow down and hold water runoff.

Because we want to minimize the chances of water passing through the roofing membrane. Therefore, it is important to pick an infill that will help keep the water retention characteristics.

Intensive green roofs have more soil depth and an increased amount of vegetation. This contributes to a higher water retention ability than extensive roofs.

Intensive roofs can significantly extend the water’s path from the soil to the root zone and enable a greater infiltration capacity of the roof. This means intensive roofs generally better handle extreme storm events and heavy rainfalls than extensive roofs.

This is because extensive green roofs typically have a few inches of soil and vegetation while intensive roofs have several inches of soil.

Install water leak detection systems

When building owners install water leak detection systems on green roofs, it can help detect any leaks in the roofing membrane.

If there are no problems detected with the waterproofing system, you will receive an all-clear signal that indicates everything is working well and your rooftop garden is safe for planting vegetation.

Once a problem has been identified, you can take the necessary steps to repair the leak and prevent it from happening again.

Insurance & Warranties

Building owners should always consult with their insurance company and green roof installer to see if the installation of a green roof system is covered under their policy.

If the green roof system is covered under your insurance, you should also check to see if there are any other restrictions or limitations that may be associated with it.

It’s important for building owners to work with their installer and receive a warranty on the installation of a green roof so they know what will happen in case something goes wrong after installation.

If you ever have to file a claim under your warranty, it’s important that the building owner has proper documentation of all work done and measurements taken. They will need this information in order to receive compensation for any repairs needed.

When is the best time of the year to install a green roof?

There is never a bad time to install a green roof. However, there are certain times that work better than others depending on the region you live in and plant type.

If you’re living in an area where winters get extremely cold and experience heavy snowfall, it’s best for building owners to wait until after winter has ended before installing their rooftop garden so they don’t have to deal with any plant damage due to the cold weather.

If you’re living in an area that only experiences mild winters, then you can install your rooftop garden during the winter months.

On the other hand, if you’re living in an area where summers are extremely hot and experience drought-like conditions, it’s best for building owners to wait until after the summer has ended before installing their rooftop garden so they don’t have to deal with any plant damage due to the harsh weather conditions.

Building owners can also look at their local government websites, community development offices, and gardening centers to see when the best time of year is for planting in their area.

Also, if you prepare everything in the fall for spring planting, the growing medium may be eroded by winter wind and runoff.

This problem could be mitigated by covering the roof with burlap or another material. The partitioning of the green roof into sections may allow for easier inspection and maintenance of the membrane and roof drains without having to pull up the entire installation.

There you have it! These are some of the best practices to follow in order to maintain your green roofs and prevent water leakage.