The expression “Living Roof” has a slightly mystifying ring to it. The phrase conjures up an image of a protective, organic, evolving, maybe even breathing formation.
In truth, this idea isn’t too far off from the real thing. A living roof (sometimes called an eco-roof or green roof) is essentially comprised of a watertight substructure, layered with several necessary growth components and planted with the appropriate vegetation. It simultaneously grows, breathes, protects and beautifies.
Though the concept may stretch the imagination, the living roof is not a new invention. In fact, even North America was home to an early civilization that fabricated buildings out of sod … and this was over 1,000 years ago.
UNESCO designated L’Anse aux Meadows, a settlement in eastern Canada believed to be founded by Viking Leif Erikson, as a national historic site and archeologists recreated a number of the region’s turf houses.
Of course, ancient civilizations settled on dirt and grass roofs for good reasons. A living roof has a number of advantages over the traditional metal or asphalt roof construction. To name a few, living roof systems reduce rainwater runoff, maintain more consistent interior temperatures, provide noise insulation, decontaminate the air and can even last longer than conventional roofs.
Also, perhaps unlike the era of the Vikings, many of today’s governments offer financial incentives to invest in eco-friendly technologies like a living roof. Quite a few people also affirm that a living roof greatly enhances the appearance of a building’s exterior.
Urban centers have an extra set of advantages. In cities, green roofs help mitigate the heat island effect, can operate as a food source, and contribute pockets of green space where “nature” may be a little harder to come by. The aesthetic improvement afforded by green roofs is hard to deny in so-called concrete jungles.
With regard to contemporary applications, there are two types of living roofs: extensive and intensive. An “extensive” system requires little or no maintenance and typically includes the following layers: a rigid base (such as plywood), insulation, waterproofing (such as asphalt), root barrier, drainage channels, filter, soil mixture, and plant layer.
The “extensive” option is lighter, thus requiring less structural reinforcement and employs drought-tolerant plants eliminating seasonal irrigation. It’s recommended that an extensive living roof have a slope less than 26.5 degrees.
On the other hand, an “intensive” system is more like a garden terrace or yard and may require an equal amount of maintenance. Basically, it is a deluxe version of the simpler extensive systems and usually includes a greater variety of plant types as well as people-friendly infrastructure, such as walkways, exterior living spaces and ornamental features (e.g. sculptures or lighting elements).
The most notable drawback to the living roof is expense. They tend to be more costly than conventional roofing assemblies. Expect to pay between $10 and $25 per square foot for an extensive living roof system, whereas an intensive system starts at around $25 and the cost can climb from there.
If you are seriously considering new construction or retrofitting a building with a living roof, include the necessary professionals during the design development phase. Have an architect or structural engineer, landscaper and/or roofer on hand for consultation during the installation process.
Over the past several decades, European countries have widely accepted the green roof as a very desirable building method. North America (among other continents) caught the “green roof bug” soon after, recognizing the many advantages of the concept.
The popularity of living roofs is on the rise and as the technology improves, applications will continue to become more affordable and accessible.
By Emily Struzik