The roofs of our commercial and institutional buildings not only transform the buildings themselves but the surrounding environment as well. Today, many architects include green roofs, also known as vegetative roofs or living roofs, in their designs.
These vegetative or green roofs can significantly reduce urban flooding, improve water quality, and protect watersheds because they reduce the volume and rate of runoff.
The United States General Services Administration (GSA) published an extensive report titled “The Benefits and Challenges of Green Roofs on Public and Commercial Buildings.”
While this most current report is a decade old, much of its information is still very relevant to plumbing engineers and architects today.
Green roofs can form a vital part of a site-level stormwater management plan, reducing peak flow rates by up to 65% and increasing the amount of time it takes for water to flow from a site into the sewer by up to three hours.
Stormwater management is so critical for municipalities that many offer tax credits and grants for the installation of green roofs and other green infrastructure. But there are plenty of benefits for the building owner as well. According to the Whole Building Design Guide, additional benefits of green roofs include:
- Improving water quality
- Reducing urban heat-island effects
- Energy conservation
- Prolonging the service life of roofing materials
- Conserving energy
- Reducing sound reflection and transmission
- Improving the aesthetic environment in both work and home settings
- Mitigation of wildlife
Much of this will depend on the type of plants grown, whether they need an irrigation system, the type of drainage layer used to eliminate excess water, and the growth medium or soil in which the plants are grown.
The drainage layers will carry the excess stormwater runoff to the roof drains and, ultimately, off the roof.
Getting excess water off a green roof surface is very important. The drainage layers, along with your additional roof drains, will prevent erosion and ponding of water. It will also ensure the sound engineering and structural integrity of the roof.
Another essential aspect of green roof design is irrigation. This is especially true for intensive and multi-use roof areas. By capturing rainwater, you can use it to irrigate either the green roof and surrounding landscaping. This practice also helps to reduce excess stormwater runoff and maintenance costs.
The Whole Building Design Guide (WBDG) points out that cities such as Seattle, Portland, and Philadelphia “advocate for a combination of LID (low impact development) practices including vegetative roofs.”
The article also mentions that some municipalities, such as Chicago, “have taken the approach of mandating vegetative roofs on new building projects because of the host of benefits it brings to built-out urban areas.”
However, some Western states’ water rights laws restrict how property owners may use rainwater, claiming it as water-of-the-state. So be advised to check with your local municipality when planning your roof design.
You can also download our Green Roof Brochure here.