How to Construct a Green Roof

Green roofs are an attractive option for some residential and commercial buildings. These innovative roofs provide extra building insulation, which leads to lower energy costs and slower roof deterioration. Green roofs often facilitate storm water management, help reduce pollution and lower noise levels. Businesses can establish an outdoor lunch or recreation area on a nicely landscaped green roof. A hospital or rehabilitative setting can install a green roof to provide a garden environment that enhances patient recovery.

Things You'll Need

• Written information on your roof structure
• Written list of green roof greenery

Instructions

1. Design your green roof system. Select an intensive or extensive green roof design compatible with your roof's characteristics. An intensive roof system requires at least 1 foot of soil for large shrubs and mature trees. This system adds considerable weight to your roof. A lightweight extensive green roof requires only 1 to 5 inches of soil. Extensive green roofs often feature ground cover and ornamental grasses. Consult with a structural engineer to determine an optimum green roof system for your particular roof.

2. Purchase your roof system permits. Visit your local building inspector's office. Obtain written confirmation that your city or town allows green roof construction. Obtain necessary building permits, environmental permits and any other special permissions. Refrain from project expenditures or construction until you have all the required permits.

3. Install your green roof membrane system. Install a waterproof membrane between your roof's surface and your green roof structure. Waterproof membranes should be constructed of a dense, inert material that prevents water or wayward roots from compromising your green roof system. Make sure that the membrane is in excellent condition, with no rips or tears. Leak-test the membrane prior to installation.

4. Install an optional insulation system. Consider an insulation system that helps prevent green roof water from affecting your heating or cooling system's efficiency. Without optional insulation, water can divert your winter heat or summer cool air away from your building. Architects often decide if an existing building requires additional insulation before beginning green roof installation.

5. Install irrigation and drainage systems. Irrigation and drainage are critical parts of your green roof system. Although your vegetation requires water to keep it growing, it is undesirable for water to pool on the rooftop. This can cause a leak and add unnecessary roof weight. Install a drainage layer that efficiently drains surplus water through a filter system. The filters allow water to drain but prohibit soil from washing away.

6. Install your plant growth medium. The green roof's growing medium provides a root anchor and a barrier between the roof and the plant structures. An intensive roof should have a lightweight mineral medium mixed with sand or any organic material except flammable peat. An extensive roof requires only a small amount of organic material mixed with the mineral medium. This mixture should be hardy enough to withstand freeze/thaw cycles.

7. Install your plants and other vegetation. Select vegetation compatible with your chosen green roof structure and climate. Populate your intensive green roof with shrubs, trees and other greenery that grows naturally in your area. Look for fast-growing ground covers and low-maintenance plants for your extensive green roof. Visit a local garden center for product recommendations. Master Gardener volunteers, available through your local cooperative extension system office, can also contribute their expertise (see the Resources section).

References

• University of Wisconsin Milwaukee: Great Lakes Water Institute Green Roof Project: Green Roof Installation
• North Carolina State University Water Quality Group: Green Roof Synopsis: Overview
• District of Columbia: District Department of the Environment: Green Roof Toolkit: Waterproof Membrane
• Greenroofs.com: Insulation
• House-Energy: Green Roof Installation: Irrigation and Drainage Layer
• City of Indianapolis Stormwater Green Infrastructure Guidance: Green Roofs: Growing Medium

Resources

• National Institute of Food and Agriculture: Cooperative Extension System Offices: Master Gardeners