Wood – a step ahead
Wood is a modern building material, for several reasons.
“Ecologically speaking, wood is a step ahead of other building
materials,” according to Klaus Richter, Head of the
Empa’s Wood Laboratory. This natural raw material is
constantly replenished by growth and is locally produced from
indigenous forests. It is also CO2 neutral, and disposal is not a
problem. So, in times when substantial added value is placed on
sustainability, wood becomes an attractive alternative to
mineral-based construction materials.
A further advantage is that wood lends a comfortable atmosphere
indoors, and wooden floors and walls are always warm and dry to the
touch. Wood removes humidity from room air when it is damp and
returns it when it is dry, so that wooden houses do not suffer from
very dry atmospheres when heated in winter. In addition, Richter
adds “Wooden houses can be prefabricated and erected very
rapidly, leaving their competitors in brick and mortar or concrete
way behind. They also play a leading role in the field of energy
efficient buildings.”
New wood-based materials – from beam to
sheet
As a building material, wood also has its disadvantages. It is by
nature inhomogeneous, the grain of the fiber running along the
direction of growth of the tree trunk. Dryness and humidity cause
wood to shrink and swell respectively, but the magnitude of the
effect varies in different directions. The mechanical strength of
wood also depends on whether it is loaded across or along the
grain.
Today it is possible to produce wood-based materials with
predefined properties. This is achieved by first shredding the wood
to produce shavings or chips, then reconstituting these using
special techniques to give the required product. “Wood today
is not just available in the traditional form of beams and planks.
For a long time now it has been available as large area
boards,” reported the next speaker, Andrea Deplazes, Professor
of Architecture und Construction at the ETH Zurich. The new
wood-derived materials are in addition dry, crack-free, and
homogeneous, so that they retain their original shape and
size.
Using solid wood and wood-based products, it is possible today to
manufacture multifunctional assemblies on an industrial scale.
These are put together to create complete systems, like a sandwich
with many-layers of functions. Complete sets of walls can be
produced in a factory and transported to the buiding site, where
they are put together using a set of assembly instructions.
“Building a wooden house today is like assembling IKEA
furniture,” maintains Deplazes, putting his finger on the
nub!
Advances in production techniques have now made it possible to use
completely different construction methods. Whilst in the past
houses were constructed primarily using concrete block or
timber-framed methods, today prefabricated wooden assemblies are
becoming more and more common. Construction using wood-based
materials is beginning to establish itself as standard building
technique. Whereas in 1990 only 2% of all new houses were of wood,
in the year 2000 this figure had climbed to 16%. In addition, in
January this year new fire prevention ordinances came into force
which permit the construction of multi-storey wooden buildings.
This allows wood constructions techniques access for the first time
to a large new segment of the building market.
Safety and protection requirements
“In terms of thermal and acoustic insulation, dampness
resistance, and from the fire-safety aspect, wood has made
noteworthy progress,” explained Stefan Winter, Professor of
Wood Construction and Structural Design at the Technical
University, Munich. Wood intrinsically has good thermal insulation
characteristics, since it is by nature a cellular material. For
this reason wooden houses often have the qualities necessary to
achieve the “Minergie” label.
Modern wood buildings are also well sealed. Well thought-through
design and careful construction ensure that no dampness can
penetrate into the wooden structure. This means that the wood used
for modern buildings does not need to be chemically treated.
“Good design and construction obviates the need for chemical
treatment” according to Prof. Winter. The idea too that wooden
houses are noisy, with poor acoustic properties, is a thing of the
past. Today there is a large range of constructional measures which
can be taken to ensure that new buildings meet current acoustic
requirements.
Finally, the danger of fire is no longer a justified fear. Wooden
houses built with fire retardant components are astonishingly
resistant to fire damage. Whereas steel and concrete rapidly lose
strength when heated, wood burns through astoundingly slowly.
“The risk of a fire is not increased by the use of an
inflammable construction material, but through the age and contents
of the building and the carelessness of its inhabitants,”
emphasizes Winter.
Wood buildings last a long time
The conclusion the three speakers arrived at was that if building
concepts and constructional techniques were adapted appropriately,
and the quality of manufacture and assembly properly supervised,
then it would be possible to erect wooden houses which would have
long useful lifetimes – as long, in fact, as brick or concrete
buildings. They demonstrated the many different applications
available to wooden buildings by the following examples: office
buildings, swimming baths, churches, bridges, industrial buildings,
inhabited dwellings and even fire stations! In summarizing, Klaus
Richter hoped that it would be the owners of a wooden building who
had the last laugh – because they had chosen the right
construction technique – and not the woodworms!
Dr.
Bärbel Zierl
Contact:
Dr.
Klaus Richter, Section Wood, phone 044 823 41 15,
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