Civil Engineering Reference
In-Depth Information
Ordinary grass turf is used for building. It should preferably be taken from old
mounds or fields to ensure that it is well bound with grass roots. If the grass is
relatively newly planted (three to four years old), the root system will be unde-
veloped, so the turf may break up when removed. Turf should not be taken from
a marsh.
Modern turf roofs often start as loose earth that is then sown with grass seed.
The recommended grasses are 70 per cent sheep's-fescue ( Festuca ovina ), 10 per
cent timothy grass ( Phleum pratense ) and 20 per cent creeping bent grass ( Agrostis
stolonifera ). In dry areas, generous amounts of house leek ( Semper vivum ) and rose
root ( Sedum roseum ), which are very resistant during dry periods, should be
added. The sedum can be sown when the Semper vivum is planted, because it will
spread through the root system. Semper vivum contains a lot of sap and therefore
has a certain degree of fire resistance. When turf roofs were common in towns,
laws ensured the use of Semper vivum on the roof.
Redcurrants, gooseberries and blackcurrants thrive in roof gardens and on flat
roofs with a deep layer of earth. Trees planted on roofs should have a very shal-
low root system, e.g. birch.
Climbing plants and hedges
Climbing plants and hedges are not used very much in building despite their
interesting characteristics. They can reduce the effect of wind, increase warmth
and sound insulation, and protect wall materials.
There are two main types of climbing plant: those that climb without support,
and those that need support.
Self-climbers
Self-climbers need no help to climb up and cover a wall. They climb by means of
small shoots that have small roots or sticky tentacles. The smallest unevenness
on the wall gives them the opportunity to fasten. Over a period of time an even
green screen will form, requiring a minimum of care. These types of plants are
best suited for high, inaccessible façades.
The most important climber in the northern European climate is ivy. It grows
slowly, but can spread out to a height of 30 m, and is evergreen.
Trellis climbers
Trellis climbers are dependent upon some form of support to be able to climb a
wall. There are three types:
• Twining plants need to twist around something to climb. They do not grow
well on horizontal planes. Wisteria, honeysuckle and hops are the most com-
mon examples.
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