The roof- the fifth façade- plays an important, but nevertheless
often neglected, roll in the energy housekeeping of a building. 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 which is directed the most
to the sun. A much-used technique in the ecological building is applying
a planted roof. Besides the technical characteristics it seems that with
this choice the 'natural' character plays a roll. Since is there a better
way to integrate the building with the nature than by letting it overgrow?
 Overgrowth of mosses, spices and plants |
 Not a dyke - a roof! |
 A grass roof |
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 and technical characteristics 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 the overgrowth adds to the necessary CO2 reduction.
Planted roofs can contain up to 50% of the rainwater that is returned
to the natural cycle by evaporation. The sewerage is therefore less strained.
-Even though the structural characteristics are strongly depending on
the chosen construction and the overgrowth, in general a planted roof
has a better heat insulation. 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
as well as by noise muffling from outside to inside the building. -planted
roofs are generally heavy and therefor require a heavier carry-construction.
jv
