Green roofs have received a thumbs-up since construction of the mythical Hanging Gardens of Babylon, one of the Seven Wonders of the Ancient World. As centuries passed, roofs using natural cover surged in popularity when home-builders discovered that coating their roof top with sod could keep their structure cool in summer and warm in winter. And a pioneering early adopter on the commercial side was Rockefeller Center, which installed its roof gardens back in the 1930s.
Fast forward to the 21st century, where architects and builders of industrial, commercial and municipal buildings―mindful of their buildings’ role within the environment―now acknowledge that vegetated roofing is a smart way to help address environmental issues such as urban heat island effect and storm-water management.
The result? Millions of square feet of eco-friendly vegetated roofing and walls are sprouting on commercial structures across North America, including 50 United Nations Plaza in San Francisco and the U.S. Coast Guard Headquarters in Washington, D.C.
How green roofs work
Green roofs effectively utilize plants in their natural habitat to filter water and treat air.
An effective green roof employs a layering system to partially or completely cover the roof with vegetation and a lightweight growing medium, planted over a waterproofing membrane. Additional layers provide a root barrier, drainage, and irrigation.
A vegetated system can be installed on any size roof, and is suited to both new construction and retrofit/redevelopment projects.
The green advantage
Once installed, green roofs offer impactful environmental gains:
- They retain, filter and cool rainwater, benefiting areas with a failing storm-water management infrastructure, and can mitigate seasonal flooding events, sewer overflow or other scenarios where environmental contaminants in storm-water runoff pose a threat.
- They provide insulation and help reduce energy use. Depending on climate zone, a dark-surfaced roof might register as hot as 180°F on a sunny summer day, compared to 75°F or cooler for a vegetated roof. Green cover allows a building to reflect and absorb radiation from the sun during the summer, and to better retain its heat during cooler months―all significantly reducing heating and cooling needs.
- They help lower air temperatures and mitigate urban heat island effect, which occurs when dark roofs, parking lots and concrete absorb and amplify heat from sunlight, causing an urban or metro area to grow measurably warmer than surrounding locales. A concentration of green roofs can literally reduce an urban area’s average temperatures during the summer, lessening urban heat island effect. Thanks to its environmental pluses, many jurisdictions (including Portland, Toronto, and San Francisco) now mandate green roofing on new commercial construction.
Vegetated roofing contributes to a healthier environment in more personal ways as well. The aesthetics of green roofs have proven to decrease stress levels and increase feelings of contentment and enjoyment for people able to view or access hospital healing gardens, lunchtime parks, and vegetable gardens. Not surprisingly, multi-tenant buildings with vegetated roofing achieve full capacity faster, retain tenants longer, and lease for more per unit than buildings without a green roof.
Green roof technologies offer practical benefits for builders as well. By shielding the roof’s membrane from ultra-violet radiation and physical damage, use of vegetation can double, or even triple, the life of the roof. And because the materials used in most green-roofing systems are salvageable, replacing a green roof costs only about 1/3 of its initial installation cost.
As a strong advocate of green building practices, Henry® Company develops and offers products that support beneficial end-results in building sustainability, maintainability, health factors, and environmental quality. Henry offers vegetated roofing systems that can be specifically tailored to each building scenario and that qualify for LEED credits. Complete systems are covered with a full system warranty.
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