1. What is a green roof?
2. Benefits of green roofs
3. How are green roofs built?
4. What should I consider when designing a green roof?
5. How much does a green roof cost and how much can it save me?
6. Are there any direct financial incentives for me to build a green roof?
7. Who can help?
1. What is a Green Roof?
A green roof is a specially designed roof that supports plant growth, reduces a building’s environmental impact and contributes to the health of people, ecosystems, and wildlife in the surrounding area.
With proper planning and design, a green roof can be installed on almost any building, regardless of climate, size, and use. There a several different types of green roofs. Designing the best green roof for your building will help the project succeed. Green roofs can be extensive or intensive.
Extensive Green Roof
2”-6” of soil depth
Supports small plants and hardy grasses
Low maintenance
Typical plantings, such as grasses and cacti are capable of surviving in draughts, high winds, and other harsh conditions
Can be installed at slopes up to 30 degrees (or higher with additional reinforcement)
Can function as a “brown” roof (where plants are allowed to arrive naturally) or full green roof where species are selected for planting
Intensive Green Roof
>6” of soil depth
Supports large plants and small trees
High maintenance
Typical plantings, such as flowers and small trees are unlikely to withstand extreme climatic conditions.
Must be installed on a relatively flat surface
Usually designed to support specific plant species, often in a designated pattern or arrangement.
2. Benefits of Green Roofs
a. Help municipalities with stormwater management by absorbing up to 70% of annual rainfall that would otherwise carry chemicals to waterways and overburden sewage treatment facilities.
b. Improve sound insulation, lowering a building’s ambient noise by up to 50 decibels.
c. Improves temperature insulation by radiating heat away from a building on hot days and providing an extra layer of protection in the cold.
d. Reduce the urban heat island effect caused by high concentrations of asphalt and concrete, keeping cities cooler by reflecting heat and cooling the air with plants.
e. Help to mitigate climate change by reducing the amount of energy needed to heat and cool a building and absorbing carbon dioxide through its plants.
f. Are more durable and cost effective than traditional roofs because the roof membrane is protected from the elements and can last two to three times as long as a conventional membrane.
g. Function as wildlife habitat by creating a green space where plants, insects, and birds can make a home in an urban environment.
h. Provide people with a green space to gather, relax, or grow a garden.
i. Allows a building to function as a healthy part of the surrounding ecosystem.
j. Contributes to a beautiful cityscape.
3. How are Green Roofs built?
Green roof designs vary, but components often include:
1. Waterproofing layer protects building from moisture.
2. Root Barrier ensures that roots do not damage the other layers.
3. Insulation helps to regulate the temperature of the building.
4. Drainage and Retention layer helps to manage water on the roof.
5. Filter fabric keeps the growing medium in place.
6. Growing medium (acts as soil) provides the support and nutrition for plants to grow.
7. Plantings, the final and most visible layer, are what make roofs green!
4. What should I consider when designing a Green Roof?
a. Many companies will help you to select components that complement each other and result in an effective roof system. Components can be purchased and installed separately or manufactured as blocks that contain multiple layers for easy installation.
b. Selecting proper plantings for your roof is crucial to the success of your project. The types of plants you should select will vary based on the climate and the specific goals of your project. Depending on the type of plants you select, there are several planting methods which vary in their effectiveness, cost, and the time it takes for plants to mature.
c. If you are adding a green roof to an existing building, be sure that you have calculated and accounted for the slope limitations and weight of your green roof. If you are doing new construction, design with a green roof in mind.
5. How much does a green roof cost and how much can it save me?
The cost of a green roof will vary widely depending on the type of roof you install; they can cost as little as $1.50 per square foot or as much as $800. Average costs in the US run between $10-$25 per sq ft . If you design your roof well, it can pay for itself in energy cost savings in as little as 10-15 years. The city of Chicago calculated that it would save $100 million dollars in energy costs annually if all the city’s roofs were green. A green roof can reduce the air conditioning costs of a single story building by up to 30%.
6. Are there any direct financial incentives for me to build a green roof?
a. Local Government Incentives
i. The cities of Chicago, IL and Portland, OR have been leaders in green roofs. These cities give grants to promote green roofs and offer stormwater management fee reductions for building with green roofs. As of October 2007, Boston did not offer incentives for green roofs.
b. Property Value
i. A study of real estate trends in Japan show that people are willing to spend more on properties with access to a green roof. As more green roofs are constructed in the US, this trend will likely continue here as well.
ii. LEED (Leadership in Energy and Environmental Design) Certification
iii. A green roof can help to earn several credits towards LEED certification, a rating system for green buildings.
7. Who can help?
General Information
Green Roofs for Healthy Cities - www.greenroofs.org
Detailed Calculator for Life Cycle cost analysis greenroofs.org/lcc_calculator/lcc_calculator.php -
Information on Products and Professionals
www.nesea.org/syp - Sustainable Green Pages
www.greenbuildingblocks.com
www.roofscapes.com/FLL.htm
http://www.greenroofs.com/directory.php
http://www.coolroofs.org/productratingprogram.html
Related books available for use at the NEXUS Resource Library
Earth Pledge. Green Roofs: Ecological Design and Construction. Atglen, PA: Schiffer Publishing Ltd., 2005.
Dunnett, Nigel and Noel Kingsbury. Planting Green Roofs and Living Walls. Portland, OR: Timber Press, Inc., 2004
Dunnet, Nigel and Andy Clayton. Rain Gardens: Managing Water Sustainably in the Garden and Designed Landscape. Portland, OR: Timber Press, Inc., 2007.
Snodgrass, Edmund C. and Lucie L. Snodgress. Green Roof Plants: A Resource and Planting Guide. Portland, OR: Timber Press, Inc., 2006.
Footnotes
1. Green Roofs: Using Roofs for More Than Keeping Dry. Environmental Building News, November 2001. Date of Access: 20 September 2007. <http://www.buildinggreen.com/auth/article.cfm?fileName=101101a.xml>
2. FAQ’s. Date of Access: 20 September 2007. http://www.greenroofs.com/Greenroofs101/faqs.htm
3. Earth Pledge. Green Roofs: Ecological Design and Construction.Atglen, PA: Schiffer Publishing Ltd, 2005., 16.
4. Green Roofs: Using Roofs for More Than Keeping Dry.
5. About Green Roofs. 31 May 2005. Green Roofs for Healthy Cities. Date of Access: 20 September 2007. < http://www.greenroofs.org/index.php?option=com_content&task=view&id=26&Itemid=40>
6. The outline of this section was borrowed from: Earth Pledge, 134-135.
7. Earth Pledge, 142
8. Green Roofs at Harvard. Harvard Green Campus Initiative. Date of Access: 20 September 2007. <http://www.greencampus.harvard.edu/hpbs/green_roofs.php#LEED>
9. Earth Pledge, 20.
10. Green Roofs: Using Roofs for More Than Keeping Dry
11. Green Roofs: Using Roofs for More Than Keeping Dry
12. Green Roofs: Ecological Design and Construction, 20.
13. http://www.greencampus.harvard.edu/hpbs/green_roofs.php#LEED