Civil Engineering Reference
In-Depth Information
the smoke must be filtered. Sheets that contain minerals cannot be burned. Waste
material left after demolition has to be dumped at special depots.
Living plant surfaces
Surfaces can be protected with living plants. These can be divided into two
groups: roof coverings of turf and wall coverings of climbing plants.
Very positive environmental qualities result from the use of plants as living
surface treatments. The exception is the waterproofing needed under a turf roof,
which is usually either a plastic or bituminous product. Trelliswork for climbing
plants should be made of high-quality non-impregnated timber.
Environmental advances with plant surfaces
Plant surfaces are an important factor in the environment of towns. Green plants bind and
break down gases such as nitrogen oxide, carbon dioxide and carbon monoxide and pro-
duce oxygen. A combined leaf surface of 150 m
2
produces the oxygen needed for one
person. A 150 m
2
roof that has 100 m
2
leaf surface per square metre supports the equiv-
alent of 100 people. A wild, overgrown grass roof produces about 20 times as much oxy-
gen as a well-looked-after lawn.
Planted surfaces bind dust, which is carried by rain to the ground. Well-planted areas
also reduce vertical air movement. Over a conventional roof, vertical air currents of up to
0.5 m/s can be caused by solar heating of the roof material. On metal roofs the tempera-
ture can be as high as 100°C. This air movement can pick up dirt and form clouds of dirt
over towns. A turf roof will reach no more than 30°C, almost totally eliminating the rising
air movement.
Planted surfaces can provide good thermal insulation. Pockets of still insulating air are
formed between the plants giving the same effect as a fluffy fur coat. Plants also reduce
the effects of wind and the infiltration of air into the underlay. A turf roof gives an insula-
tion of 46 dBA with 20 cm thickness and about 40 dBA with 12 cm thickness. This sort of
roof is therefore particularly suitable near airports.
A large part of the year, the planted surface acts as a solar panel - turf roofs have a
particularly high absorption coefficient. The plants develop their own warmth during the
cold part of the year and prevent freezing. During the summer, dew will form on the roof
in the morning. For every litre that condenses, an amount of warmth the equivalent of
0.65 kWh is emitted. The damp earth in the turf roof has a large capacity to store warmth.
This can give the building a stable, warm, indoor climate during the winter, and a cool
indoor climate in the summer. Walls covered in plants are cooled by their shade during the
summer.
Turf roofs
Turf can be used as a cladding material on mounds along walls, but is more
often used as a roof covering. Turf roofs are built up in several layers, the most
