How Many Leed Credits Can I Receive
Green roofs can facilitate a significant improvement in the LEED rating of a building, contributing as many as 15 credits under the system, depending on design and level of integration with other building systems. In some instances, while green roofs may not contribute directly to achieving points under the system, they contribute to earning LEED credits when used with other sustainable building elements. For example, green roofs can earn direct credits under the following:
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Reducing Site Disturbance, Protect or Restore Open Space
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Landscape Design That Reduces Urban Heat Islands, Roof
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Storm Water Management
Future Green Roof Research Needs
The report outlines research needs , including:
- Stormwater and storm dynamics, field monitoring and computer simulation
- Long-term stormwater and energy performance
- Establishing native plants and creating habitat for endangered fauna on green roofs
- A thorough comparison between green and white roofs
- Interaction between green roofs and solar panels
- Economics of rooftop agriculture
- Air quality improvements associated with green roofs
Visit SFTool.gov for more information on green roofs.
What Is A Green Roof
Green roofs also called living roofs, eco-roofs and vegetative roofs feature plants growing on top of a man-made structure. They include a hefty waterproofing layer, soil or other growing medium, and usually a root barrier, plus drainage and irrigation systems.
What we build most is what I call an eco-roof, says Mumford. Its got four to six inches of soil and native plants, to use as little water as possible.
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Negatives Of Green Roofing
While green roofing can benefit you and the community, it is a costly process that can lead to some unforeseen expenses:
- Insurance for green roofs is important, due to the potential of droughts or unforeseen storms, but also is expensive.
- The weight of the green roof may result in liability issues if the pressure of it causes sagging.
- Any damage the plants might do to the building, such as the roots growing into the shingles, will result in costly repairs.
Have questions about how much it costs to repair or replace your roof? You may be interested in our roofing cost guide.
Intensive Vs Extensive Green Roof
It should be clear from the above which green roof type is best for you.
In summary:
If you are looking for a low maintenance, lightweight green roof that features simple and self-maintaining vegetation then the extensive green roof is for you. These can easily be installed on sheds and garages. You can still enjoy the benefits of better sound protection, improved thermal performance and a cooling effect in hotter months.
However, if variety is what youre after and you want your green roof to support larger, more diverse plants and bushes then you should opt for the intensive option. You will need to pay more attention to structural loading, irrigation, and long term ongoing maintenance.
With an intensive roof you get a more impressive and landscaped look to your rooftop garden that can attract wildlife as well as benefitting from warmer spaces in winter and cooler spaces in summer.
For more information on green roof maintenance read our guide.
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How Are Green Roofs Made
Modern green extensive roof systems are from 1 to 4 inches thick and are composed of manufactured layers that support a growing medium and vegetation. The five primary layers include a waterproof membrane, a root protection barrier, a drainage layer, a growing medium, and plants.
Above: A diagram of a green roof and its component layers. Image via Safeguard Store.
How Much Maintenance Does A Green Roof Require
At the minimum, an extensive 4-inch green roof system planted with mixed sedums in its first year requires watering and weeding every few months. In the second year, it only will need to be weeded three or four times and after that, just once a year. You will need to fertilize once a year.
At the other end of the spectrum, depending on what you plant, maintenance requirements can increase to the point where you might want to consider an irrigation system. See Hardscaping 101: Drip Irrigation for details.
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Green Roofs On Historic Buildings: Green Roof Benefits
Economic Benefits
Although installation of a green roof usually involves higher upfront costs than a traditional roof, there are many economic benefits that can make up for this. Increased Rvalue of the roofing system, along with reduced temperatures on the roof lessen HVAC loads, resulting in energy cost savings. A green roof may improve property values and marketability, especially in urban areas with little green space. The University of Michigan performed a valuation study comparing a 2,000 square meter conventional roof and a green roof. The study looked at a range of benefits of green roofs including stormwater management, improved health benefits due to reduced pollution, and energy savings. Over its estimated lifespan of 40 years a green roof would save about $200,000, of which, nearly twothirds would come from reduced energy costs. The economic benefits of any individual green roof will, however, depend on its design, geographic location, surroundings, and the building itself.
Improves Stormwater Management
Reduces Urban Heat Island Effect and Improves Air Quality
Insulates the Building
Improves Efficiency of Mechanical Equipment
Reduces Greenhouse Gas Emissions
Extends Roof Life
Courtesy of the City of Chicago
Provides Urban Amenities
Did you know?
A green roof can actually be installed at ground level. These types of green roofs are often installed as the roof of a parking garage or another underground building.
What Are The Benefits Of A Green Roof System
The great thing about green roofs is that they tick so many boxes for sustainability, technology and aesthetics. If youre investing in a green roof, its important to know exactly what the benefits are so that you get a great return on investment:
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Roof membrane protection – vegetation on a roof deck protects the roof surface from the extremes of weather, temperature and UV radiation, which can significantly prolong its life
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Reduced storm water run-off – water is stored by the green roof substrate and then taken up by the plants, where it is returned through transpiration and evaporation into the atmosphere. The drainage layer in green roofs also delay the rate at which water run-off occurs, resulting in decreased stress on drains and sewers during periods of heavy rainfall
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Reduced energy costs – The layers of a green roof system are able to improve the thermal performance of the roof, helping to keep the rooms below cool in summer and warm in winter, although this effect is generally not included in any uValue calculations
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How Much Does A Green Roof Cost
The cost of a green roof varies considerably depending on the type and factors such as the depth of growing medium, selected plants, size of installation, use of irrigation, and whether they are to be accessible on inaccessible – intensive, semi-intensive, or extensive. Intensive green roofs typically require greater investment but confer the benefits of accessibility. An installed extensive green roof with root repellent/waterproof membranes may be installed for $10-$24 per square foot. While green roofs typically require a greater initial investment, it is important to keep in mind that they can extend the life of the roof membrane and reduce the heating and cooling costs of your building. Speak to a qualified Green Roof Professional about the range of costs and benefits for different green roof systems and designs.
Operation & Maintenance Costs
Its important that you understand how green roof maintenance is carried out.
Consider the following:
- Is your maintenance performed by you or by a 3rd party?
- What materials need to be replaced?
- How is the climate in your area?
- What plant species do you have?
- How much irrigation do you need to perform?
Although there is no data related to maintenance cost reduction over the years, usually extensive green roofs require less maintenance than intensive green roofs.
In the first years, green roofs usually have more irrigation needs and re-planting may be needed due to plant inadaptation.
The below figure shows the operation and maintenance costs of extensive, semi-intensive, and intensive green roofs obtained from the following .
The average maintenance costs vary significantly from country to country and are as follows:
- Extensive green roof -4,28 /m2/year
- Semi-intensive green roof 7,77 /m2/year
- Intensive green roof 5,64 /m2/year
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Benefits Of Green Roofs
Green roofs can be placed on both old and new buildings. The green roof system can either be modular, with drainage layers, guttering, filter cloth, growing media and plants already prepared in movable, often interlocking grids, or loose laid/ built-up where each component of the system may be installed separately.
Reports vary on installation costs but on average extensive green roof range between $8 and $20 per square foot and intensive green roofs range between $15 and $50 per square foot. This compared to a traditional roof installation which averages about $16 dollars per square foot the green roof installation costs tend to be much higher. Although a higher installation cost is required, the green roof undoubtedly offers more benefits than a traditional roof may offer.
Green roofs have the potential to reduce energy demands two ways: absorbing heat and acting as insulators for buildings. Adding a layer of soil and plants to a roof adds insulation to the building it covers. Since roofs are the site of the greatest heat loss in the winter and the hottest temperatures in the summer, the greater insulation offered by green roofs can decrease the amount of energy required to moderate the temperature of a building.
Chongqing Taoyuanju Community Center Chongqing China
A continuous green roof connects the three separate structures of the Chongqing Taoyuanju Community Center, including cultural, athletics, and public health facilities, to each other as well as to the surrounding landscape. Vector Architects created a ring-shaped layout for the sprawling complex, which follows the existing topography of its site in the mountains of Taoyuan Park.
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Green Roof Waterproof Drainage Membranes
The drainage layer of a green roof system is vitally important. It deals with rain and storm water, allowing it to drain safely away from the roof and into guttering and downpipes. By dealing with excess water, it prevents damage to the structure as well as to the plants from saturation and root damage. These green roof drainage membranes feature a stud profile that helps ensure adequate drainage.
Our PermaSEAL 8 Green Roof Membrane is suitable as a drainage membrane for extensive and intensive green roofs. Membranes like our PermaSEAL 20P Green Roof Membrane combine drainage and water storage to help ensure the long term health of your living roof.
We cover green roof drainage in more detail later on.
Where Can I Learn More About Green Roofs
GRHC’s Education Program is the source for the most comprehensive information on green roofs and walls in North America.
For general information on green roofs and walls, please check out the rest of our website and the Living Architecture Monitor magazine. More information can also be found on some of our Members’ web sites.
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Green Roofs Are Sprouting Up Everywhere Thanks To Their Aesthetics Sustainability And Long
Green roofs have been around at least since the time of the Vikings, who laid birch bark and sod on top of wooden boards to make their homes more draft-proof. Their modern incarnation began in 1960s Europe.
Germany started looking at green roofs as a way to cut down on the spread of wildfires, says Jim Mumford, president and resident horticulturist at Good Earth Plant Company in San Diego. And then it came across the Atlantic.
Today, Europe is still the leader in green roofs. But a number of U.S. cities are embracing the benefits, giving incentives to homeowners to install them. New York, Portland, Denver and Nashville require them in new construction of a certain size. Today, even the McDonalds world headquarters in Chicago sports a fuzzy, green top.
One of the things I really like about it is the addition of biodiversity, says Mumford. Ive got milkweed all over mine, so I see butterflies all the time, and birds and bees. Its a nice little wild spot.
Whether youve been dreaming of a green roof for years or are just a little curious, heres how to decide if a living roof is right for your home.
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Minimizing Green Roof Leaks
So how do you go about reducing the chances of a leak occurring?
Firstly, a walk-through inspection usually takes place with a roofing consultant and general contractor prior to installing the membrane layer of the roof.
But before you install your membrane layer, its vital that you prepare your deck surface adequately.
After you install your membrane layer, you then need to conduct a membrane leak detection test. This will ensure that your membrane doesnt have any leaks before you go about adding any further green roof layers to your system.
You must not skip this step. Without it, you wont be able to identify design and construction errors and as such, you cant protect yourself under the terms of your roofing contract and warranty.
If youre concerned about leaks occurring throughout the lifespan of your room, there are automatic leak detection systems out there. These will notify you of any leaks after the installation of your green roof.
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How Much Does It Cost To Install A Green Roof
The good news is that with an extensive green roof on a flat roof you can do the install yourself at no additional cost. If you want to get someone else to install the green roof, then the cost of green roof installation will depend on the contractor. Be sure to ask lots of questions around the design and how long it will take. Its best to get a few different quotes to compare before opting for one contractor.
Green Roof Growing Substrate
To successfully grow vegetation on your green roof, you need to choose the right substrate or growing medium. It is a common mistake to think that you can only use soil. This is not the case and is frequently not the best option.
It is also a common mistake that sedum mats and sedum blankets dont require an additional growing medium and can be laid upon the drainage and filter layers. Although the roots of a sedum blanket are relatively shallow, we would always advise that additional growing medium is provided. A depth of 50mm works best but a minimum depth of 20mm is acceptable in some cases.
For other types of vegetation, you want a growing substrate that is light-weight, aids with drainage but is absorbent enough to retain water to adequately support your plant growth. Its a fine balance and will depend on what you plan on growing.
Many green roof growing mediums are specially designed, being a custom blend of aggregate and organic materials based on your needs.
There are various green roof substrates on the market. These often include a few different materials blended together to create the characteristics needed for good vegetation growth. These include bricks and aggregates, compost, medium clay soils and even volcanic rocks like lava and pumice .
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Green Roof Cost Benefit Analysis
The report includes the cost benefit analysis for green roofs as well, and offers data including:
- GSA green roof report estimated that green roofs on commercial and public buildings provide a payback, based on 50 year average annual savings, of about 6.2 years nationally, internal rate of return of 5.2%, and an ROI of 224%, based on a net present value of $2.7/square foot.
- Primary green roof costs are related to installation and maintenance.
- Primary economic benefits of installing green roofs are lower energy costs, less frequent roof replacement due to greater durability, reduced stormwater management costs, and creation of job opportunities.
Why Germany Is At The Forefront Of Green Roofing
In 1998, after visiting Germany and seeing their green roof developments, the Mayor of Chicago directed municipal funds towards creating them in his own city. Germany has been working to green its technologies for the last 40 years or more, long before it became a necessity for the rest of us. The country now retains a dominant share of the renewables market and a large proportion of its working population are employed within the industry.
Most of the guidelines that have been developed for creating and sustaining a green roof have come from Germany and by 2001 43% of cities in the country were providing incentives for installing one on their roofs.
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Costs Of Installing And Maintaining Green Roofs
The estimated costs of installing and maintaining a green roof vary by the type of green roof. For example, a simple extensive roof without public access could be as little as one-tenth to one-third of the cost to construct an intensive green roof intended for public access.8 While the initial costs of green roofs can be higher than those of conventional materials, building owners can help offset some of the differences in these costs through reduced energy costs and stormwater management fees, and potentially by the longer lifespan of green roofs compared with conventional roofing materials. Typical maintenance includes fertilization, irrigation, weed control, and replanting when necessary. Intensive green roofs might require maintenance exceeding that required for extensive roofs to maintain their aesthetic and public access uses.
Researchers at Lawrence Berkeley National Laboratory conducted a lifecycle cost analysis of green roofs, cool roofs, and conventional roofs.8 They found that while green roofs are more expensive than cool or conventional roofs, they provide significantly higher relative benefits per square foot over a 50-year lifecycle . Compared to conventional roofs, the benefits of extensive green roofs are $14 more per square foot, while cool roofs provide benefits of $2 more per square foot relative to conventional roofs.
