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Green Roofs

A green roof is a rooftop partially or completely covered with a specifically designed soil and vegetation system. Green roofs create living gardens on top of buildings and structures that help to capture rainfall and reduce stormwater runoff. This captured water may be used by plants on the roof, released back to the atmosphere through evaporation, or it can be reused in other locations on the property.

Image of a green roof.

Green roofs are a roof system that includes a waterproof membrane, filter fabric, drainage layer, root barrier, growing medium (soil), and plants. Green roofs may be constructed using modular units that contain all components listed above, or the components may be installed step-by-step directly on the building’s roof deck.

 

Types of Green Roofs

The two main types of green roofs are extensive or intensive green roofs.

  • Intensive roofs are thicker, heavier, and are designed to support trees and larger shrubs

  • Extensive green roofs are typically lighter and thinner, and are designed to support plants like sedum.

Currently, only extensive green roofs constructed on existing buildings (retrofits), whether applied in an integrated approach (applying the layered components directly onto the roof’s surface) or in modular units (placed on top of the existing roof), are eligible for rebates under the  RainScapes Rewards Rebates program. Green roofs for new construction are not eligible for rebates at this time.

 

What are the Benefits of an Extensive Green Roof?

Extensive green roofs are designed to be lightweight and to maximize the performance and environmental benefits that a green roof can bring to a building. They feature a layer of growing media that is 6-inches deep or less and are planted with drought-tolerant plants. Extensive systems require less maintenance and have simpler irrigation and drainage systems, if they have any at all. Existing roofs on porches, garages, sheds, and sunrooms are excellent candidates for extensive green roof retrofits.

 

Why Should I Install a Green Roof?

Green roofs capture rainfall, and slow and reduce runoff. As stormwater filters through the soil and is taken in through plant root systems, pollutants are absorbed, reducing the volume of pollutants that enter nearby streams. Water (that is not used by the roof plants or released to the atmosphere) is filtered and can be directed to other facilities such as dry wells or rain gardens, which provide additional treatment and infiltration. Excess water may also be directed to and stored in rain barrels or cisterns and used for irrigation of the roof itself or other landscaped areas in times of little rainfall.

By doing things like this, the amount of runoff from your property is greatly reduced, which can help to protect nearby streams and rivers.

  • Green roofs provide building insulation, which often results in decreased heating and cooling costs.

  • The soil and plants of a green roof protect the building’s roof membrane from ultraviolet rays that break down conventional roofs. For this reason, green roofs have been shown to last up to twice as long as conventional roofs, reducing overall replacement and maintenance costs.

  • A green roof enables you to play a role in preserving the environment and conserving water resources.

  • This practice may also increase your property value through increased visual appeal and lower energy bills.

However, the most important reason to install a green roof may be that you are doing your part to help the environment and protect your local streams and the Chesapeake Bay. 

 

 

 

 

Is a Green Roof Right for Me?

If you are interested in installing a green roof on your property, you should contact a certified green roof contractor to make an assessment of your property.  A green roof is not recommended as a do-it-yourself project, and a contractor will be able to properly explain installation and maintenance issues, including:

  • Green roofs are expensive (the cost can be recouped if you plan to be in the building a long time, as they can provide a longer roof life and decrease building energy usage)

  • They must be properly designed and installed by a certified contractor

  • They have weight load restrictions (however, modular systems reduce this problem)

  • They need a maintenance plan, which includes seasonal roof drain inspection and weeding

Image of the front of the RainScapes Green Roof Guide
Need Help Determining If a Green Roof is Right for You? 
Download the Guide. (PDF, 334KB)
 

 

How to Assess Your Property

A qualified roofing contractor, who may be assisted by a landscape architect, is critical to the success of your system. A contractor who is experienced in green roof installations may assist with the selection of materials and placement of products, and help you assess your property.

When considering installing a green roof you should evaluate the condition of your current roof and have a licensed professional evaluate its structural capacity.

  • The amount of weight (load) your roof can sustain will determine the type of green roof product to select as well as whether you can cover the entire roof or only a portion of the roof.
  • The load capacity of your roof will also determine the maximum soil depth your system can have. The roof must be designed with a minimum of 4 inches of soil but no more than 6 inches, to qualify for the rebate.
  • You will also need to determine the slope and amount of drainage from your current roof. If your building has a flat roof, you will need an additional drainage layer and steeper roofs will require additional tools to hold soil in place. While it is possible to install a green roof on rooftops with slopes of up to 40 degrees, a 5 to 20 degree slope is optimal to ensure excess runoff can drain naturally.

If a green roof is feasible, assess the amount of sun and wind exposure your green roof is likely to experience. Green roofs are most successful with full or partial sunlight. Your plant selections will depend on these factors, as well as the amount of rainfall the roof is to receive and the soil depth your roof can support.

It is also important to consider maintenance and accessibility of the system, and the amount of maintenance required for the plants you select. To receive a RainScapes Rewards Rebate you will also need to ensure that your green roof area is at least 300 square feet or one-quarter of the roof area (whichever is smaller). The green roof must also replace an existing roof area rather than expand the original roof footprint.

Graphic of a green roof

 

Installing Your Green Roof

Work with your certified green roof contractor and other professionals to install your green roof.  The RainScapes Green Roof Guide (below) has suggestions and useful information on the best questions to ask your contractor and tips for building the green roof, cost and maintenance.  

The RainScapes program has knowledgeable and helpful staff who can help you through the process as well as the RainScapes Rewards Rebates program with great financial incentives for installing the green roof.  

 

Download the RainScapes Green Roof Guide (PDF, 334KB)

 
 

Maintaining Green Roofs

As the property owner, you are responsible for all maintenance of your green roof. DEP recommends that a qualified roofing contractor perform regular inspections of your green roof. Maintenance contracts with the manufacturers of proprietary green roof systems are recommended. 

Green roofs require regular maintenance similar to other landscaped areas, including removing debris from drains and weeding. 

An unmaintained green roof may:

  • Be difficult or expensive to restore if left unmaintained

  • Allow water to pool on the surface long enough for insects to breed (longer than 3 days), if the drains are clogged

By maintaining your green roof, you are doing your part to help the environment and protect your local streams and the Chesapeake Bay.

 

Image of the front of the Green Roof Maintenance Fact Sheet.
Need Help with Maintaining Your Green Roof?  
Download the Fact Sheet 
(PDF, 483KB)
 

 

Actions You Can Take to Maintain Your Green Roof
Seasonal Actions Annually As Needed Actions

✔ Remove weeds and invasive plants regularly during the first 18 months and at least twice a year after plants are established.

✔ Check the entire system to ensure the green roof is functioning properly and is not ponding water in any location.
✔ Water the green roof’s soil and vegetation during the 
first 18 months and during extreme droughts.
✔ Inspect the drain inlets and outlets and remove any blockages.  ✔ Observe the health and coverage of vegetation to determine whether any plants need to be replaced. See the Vegetated Facility Maintenance Guidance Document for more information.
✔  Only if needed during the plant establishment period, use fertilizer 
sparingly. Since a green roof is a stormwater management practice, 
it is important to not have any excess nutrients leaving the roof. 
  ✔ Annually inspect the irrigation system (if present).  

 

DEP can answer your questions and provide additional guidance about maintaining your green roof.

Please email askdep@montgomerycountymd.gov or call the Montgomery County Customer Service Center at 3-1-1.

 

Green Roofs in the Stormwater Facilities Maintenance Program

The Stormwater Facilities Maintenance Program is responsible for maintaining all public stormwater facilities as well as all private facilities that transfered their maintenance to the County.  The program also maintains facilities that were required as part of the Department of Planning permits.

Not sure if your green roof is part of the Stormwater Facilities Maintenance Program? Check out online Facilities Map or email askdep@montgomerycountymd.gov

 

Can I remove my green roof after installation?

No, you cannot remove any facilities that were part of your building installation - these are permitted structures and DEP maintains a database of these facility locations as part of the Stormwater Facility Maintenance Program. DEP may perform a maintenance inspection of your practice if it is a permitted structure.  Property owners must contact DEP before any major changes can be performed to the structure. 

 

Rebates, Resources and Financial Incentives

Interested in installing a green roof?  The County offers incentives to help make the decision a little easier.

 

Logo of the RainScapes programThe RainScapes Rewards Rebates Program

The County offers technical and financial assistance (in the form of rebates) to encourage property owners to implement RainScapes Rewards Rebates techniques on their property, including green roofs.

  • Residential properties are eligible for up to a $2,500 rebate

  • Commercial, multi-family or institutional properties are eligible for up to a $10,000 rebates.

To participate, your property must be located in Montgomery County, outside of the municipal limits of the City of Rockville, City of Takoma Park, or City of Gaithersburg. Projects are not eligible if they are associated with permit approval requirements for new building construction, additions, or renovations.

​The program is funded each fiscal year (The fiscal year begins July 1 and ends June 30). Annual funds for the programs are limited, so rebates will be awarded on a first-come-first-served basis.

The RainScapes program also provides technical assistance to help with the installation of your green roof. They have a wealth of information, expertise and want to help!

Learn more on the RainScape Rewards Rebates webpage. 

 

Image of a green roof.

 

The Water Quality Protection Charge Credit Program

After you have installed your green roof, you are now eligible to receive a credit off your annual Water Quality Protection Charge (found on your yearly property tax bill).  The credit provides an incentive for maintaining your green roof and other stormwater management practices.

You must apply for the WQPC credit separately – the credit will not be provided to you automatically.

Residential property owners can receive up to 50% off their WQPC depending on the type and size of stormwater management practices on the property.

Non-residential and multi-family properties can receive up to 50-60% off their WQPC depending on the type and size of the stormwater management practices on the property. 

Learn more on the WQPC Credit webpage.