What Is a Living Roof?
Living roofs, also known as green roofs, are roofs that have plants growing on them. This includes potted and unpotted plants. Living roofs are layered constructions that take the place of bare roofs, and the plants can either completely or partially cover the roof structure.
Are There Different Kinds of Living Roofs?
The three types of living roofs are intensive, extensive, and semi-intensive, also referred to as semi-extensive. Intensive living roofs are essentially elevated parks, and they encourage human interaction with nature. Intensive living roofs tend to be built on top of industrial buildings because their heavy weight requires a strong, sturdy structure to hold them. On the other hand, extensive living roofs are lightweight and perfect for smaller structures like homes. Unlike intensive living roofs, extensive roofs usually exist solely for their environmental benefits and offer no human interaction except the light maintenance they require. Semi-intensive living roofs combined elements of both intensive and extensive roofs.
Living Roofs at the Nature Center
Straw Bale Bike Pavilion Living Roof
The PCEI Nature Center has two living roofs. The first was constructed along with and on top of our straw bale bike pavilion in 2005 with the help of architect student volunteers from the University of Idaho under the direction of Kurt Rathman. PCEI used a variety of geotextiles – absorbent fabrics which help separate, filter, reinforce, protect, and drain when used with soil to build the eight-layered extensive living roof and brought it to life in 2006. The plants chosen are hardy, drought-tolerant spreading stonecrops like Autumn Fire, Dragon’s Blood, Red Carpet, Rupestre Angelina, and Vera Jameson.
Artist Studio Living Roof
The second living roof was built on top of the Artist Studio in 2009. The project was one of three community workshops in correspondence with the completion of the Artist Studio. Like the bike pavilion’s living roof, the artist studio’s roof is extensive and holds drought-tolerant stonecrops that thrive with little maintenance.
Although both are extensive living roofs, each is layered slightly differently and built to fit its unique water-supping structure.
Why Build a Living Roof?
Living roofs have many environmental benefits. They:
- provide extra green space to help with the conversion of CO2 into oxygen;
- help to naturally cool the room below in hot weather and provide extra insulation in cold weather;
- extend the roof life by protecting against the effects of ultra-violet light (UV rays) and harsh weather
- create habitats for wildlife; and
- retain water before in evaporates into the atmosphere – during heavy rainfall this characteristic has the potential of reducing the likelihood of floods
How to Construct a Living Roof
Before beginning a living roof project, it is important to determine the strength of the structure that will hold it. If the structure is not strong enough, you will need to reinforce the roof with a sturdier framework. It is a good idea to consult a structural engineer to determine the safety of your living roof.
Once the safety of the roof is ensured, the living roof construction can begin. Depending on the type of living roof you choose to construct, you will need a variation of layers, however, all three types require a protective barrier, a water drainage layer, a growing medium, and plants. the root barrier stops roots from penetrating he structure below and is a crucial layer because it also stops the roof from leaking. the water drainage layer retains water for plants and directs excess water into gutters. The growing medium should be a mixture of clean soil (potting soils are better than top soil because they are lighter and cleaner), compost, and inorganic material, such as slate, shale. extruded clay, rock wool, lava or pumice. The plant selection will depend on the type of living roof, but for extensive living roofs, hardy, drought tolerant plants are best.