It wasn’t easy being green 10 years ago when Richard Meyer and Martie Goebel of Annandale, wanted to put a living roof on the garden shed they were building. It took months of resourceful research to find the information they needed to build the small-scale roof successfully.
Today the idea for small-scale green or living roofs has taken off. Information and resources abound, making it easy for homeowners to enjoy the benefits of a beautiful living roof in their own backyard.
Green or living roofs have their roots in ancient times when sod roofs were used as insulation for cottages. It was in Germany in the 1960s that the ancient concept was reintroduced. Today a large percentage of commercial buildings in Germany — and in many other European countries — have living roofs. For example, Munich has more than 3 million square meters of green roofs, approximately the same size as Munich’s famous park known as the Englische Garten, one of the largest urban parks in the world. Stuttgart has 1.21 million square meters and Hamburg 1.25 million square meters of green roofs. In 2016, San Francisco was the first U.S. city to require that certain new buildings, including bus stop shelters, be built with green roofs.
Green roofs are beautiful, replacing a hard surface roof with a raised garden bed. Environmentally, they are wonder workers. The insulation they provide reduces energy costs, a fact that will save significantly on heating and cooling for say an in-garden man cave, she shed or enclosed pavilion.
While they are saving energy, the plants also are cleaning the air as they gather and absorb carbon dioxide, work their chemical magic and release it back into the air as pure oxygen. Meanwhile, the plant roots are filtering air pollution particles and sponging up rainwater. Thus, they perform remarkable stormwater management, reducing the demand on sewer systems by as much as 50 to 70 percent of annual rainfall on the roof and cleaning the water that does run off. When rainwater runs off solid surfaces, pollutants such as oil, pesticides, sediments, bacteria and other chemicals are deposited into the waterways.
In highly paved urban and suburban areas, green roofs also reduce the heat island effect caused by hard surfaces such as roofs and pavements that absorb heat and re-radiate it. In contrast, the surface of a vegetated rooftop can be cooler than the air temperature, while the surface of a traditional rooftop can be as much as 80 degrees hotter.
A green roof contributes to biodiversity and benefits wildlife, attracting butterflies, birds and pollinators.
Finally, while more expensive up front to build than a traditional hard-surface roof, a green roof will last longer since the materials that sun and weather can degrade are underground. A typical roof will last about 20 years; a green roof is expected to last two to three times longer. Accountants calculate that homeowners will recoup their green roof investment within eight to 21 years.
Two Types of Living Roofs
There are two kinds of living roofs: extensive systems and intensive.
Extensive roof systems typically have a 6-inch deep growing medium that can support a range of shallow-rooted plants such as sedum, chives and meadow grasses. These roofs can be either modular, where the vegetation and planting medium are contained in special trays covering all or most of the roof, or non-modular, where the planting medium is a continuous layer over the entire space.
This is the type that most homeowners would choose for a garden structure or even the roof of their house. The installation and maintenance costs are relatively low, and the prices are dropping as more people are building them.
Intensive green roofs are deeper and can sustain a complex landscape of small trees, shrubs, ponds and fountains. Buildings crowned with intensive systems must be built to support much more weight than an extensive system and are much more expensive to install. This type of system is suitable for commercial buildings and apartments.
Building Your Own Living Roof
There are books and manuals on the market with detailed instructions for building a living roof.
Briefly, the roof is built with a series of layers that insures the system performs properly. The layers will vary slightly depending on the builder, but typically are as follows:
1. Roof platform. Be sure the structure can support the added weight, including the roof structure itself.
2. Roofing membrane seal. A seamless pond liner made of heavy-duty EPDM (ethylene propylene diene monomer rubber) works well.
3. Root barrier membrane. It keeps the underneath layers from being penetrated by roots.
4. Insulation barrier, required by most building codes, despite insulation provided by plants.
5. Water retention mat. Reduces effects of drought cycles.
6. Water drainage and aeration. Layer through which water flows off the building.
7. Filter. Allows water to flow without washing away the planting medium.
8. Ultra-lightweight planting medium. Generally, this is a synthetically produced expanded clay that is less dense and more absorbent than natural minerals.
9. Plants, usually ground covers that can thrive in shallow soils with little to no maintenance.
Join the worldwide trend by incorporating a living roof in an outbuilding structure such as a garden shed or gazebo — or even on the roof of your house.