The roof is the fifth facade of a building and can play an important, but nevertheless often neglected, roll for the building and its surroundings. In many cases it takes account for a large part of the total outside area of a building and above that the roof is the part of the building directed the most to the sun. A possibility to make use of the roof instead of neglecting it is to make a planted roof. Besides the technical characteristics it seems that with this choice the 'natural' character plays a roll. Can you think of a better way to integrate the building with nature than by simply putting the nature that was replaced by the building on top of that building?
A planted roof mainly consists of the following parts:
- the overgrowth; seedlings, mosses, grasses, spices and other plants, and depending on the thickness of the substrate layer even larger scrubs and small trees.
- the substrate layer; organic material, sometimes complemented with inorganic or even artificial material in which the plants grow.
- a water passing filter-membrane that separates the substrate layer from the underlying layers.
- drainage-elements or -material
- sliding and protecting layers, a root stopping layer, and a water stopping layer, either by itself or combined.
- the carrying roof construction, possibly completed with an extra heat-insulating layer.
The environmental advantages of a planted roof are:
- with respect to the surroundings a planted roof provides a natural climate control because it has a stabilising function on changes in temperature and air humidity. A planted roof can filter air pollution from the surroundings and can add to the necessary CO2 reduction.
- planted roofs can store up to 50% of the rainwater. This water is returned to the natural cycle by evaporation. Also the the water that comes from the roof is slowed down in time by the planted roof. Both result in less pressure on the sewerage system.
- even though the structural characteristics are strongly depending on the chosen construction and planting, a planted roof can have a better heat insulation, mostly due to the insulation layers. In the winter however the streams of rainwater can create a detrimental effect.
- by the slow evaporation of the moisture in the overgrown layer the construction has an extra muffling function with respect to temperature fluctuations
- planted roofs have a noise muffling function for their surroundings because of their rough surface. There's also noise muffling from outside to inside the building because of the mass of the planted roof.
That a planted roof can also be a smart way to cut on the budget is illustrated by the following example:
In 1999 Architect William McDonough entered into an agreement with Ford Motor Company to redesign its 85-year-old Rouge River facility. The roof of the 100,000 m2 Dearborn truck assembly plant was covered with more than 40,000 m2 of sedum. The sedum retains and cleanses rain water, as well as moderating the internal temperature of the building, to save energy. The roof is part of an $18 million rainwater treatment system designed to clean 76 million m3 of rainwater annually, and sparing Ford from a $50 million mechanical treatment facility.
JV & DDL
Peter G. Teeuw, Christophe Ravesloot: Begroeide daken in Nederland, Delft, 1998 (NL)