Wooden Houses of Anatolia
Wood as a Building Material; It's Benefits and Disadvantages
For the long term durability of historical wooden buildings, constructors and
users who deal with this subject have to know wood properties exactly.
Wood is an organic, hygroscopic and anisotropic material. Its thermal,
acoustic, electrical, mechanical, aesthetic, working, etc. properties are very
suitable to use it is possible to build a comfortable house using only wooden
products. With other materials, it is almost impossible. But wood has some
disadvantages too. Following is some very short information about this subject.
BENEFITS OF WOOD
As we know, many, materials change in size and volume as the temperature
changes. They expand with increasing of the temperature. This means linear and
volumetric expansion. The expansion. The expansion causes decrease in the
strength of materials. Steel, which is inorganic and non-combustible and
therefore has an advantage against fire, but when used in buildings, it expands
and collapses as a result of increase in heat.
Wood does not practically expand against heat. On the contrary, by the effect
of heat, it dries out and gains strength. The only time wood expands a little is
when the humidity level is below 0%, and this is only scientifically
significant. In practice, the humidity level of wood does not drop under 5% even
in the driest climate.
The coefficient of thermal conductivity of the wood is very low. Aluminium
transmits heat 7000 times, steal 1650 times, marble 90 times and glass 23 times
faster than wood. For this reason, wood is used for making matches, handles of
hardware equipment, ceilings and wall coverings.
Specific heat of wood is high. That means high amount of energy is needed to
increase and decrease the temperature of one-kilogram of wood. Wood requires
almost twice amount of heat energy than stones and concrete; similarly, three
times of energy is needed for heating or cooling steel.
Sound isolation is based on the mass of the surface. Wood, as a light
material, is not very perfect for sound isolation; But it is ideal for sound
absorption. Wood prevents echo and noise by absorbing sound. For this reason it
is extensively used in concert halls.
Sound velocity is faster in woods than gases and liquids, and it is close to
that of metals. Sound energy loss as a result of friction is also significantly
low in woods due to its lightness and structure. Because of such properties,
wood is extensively used in musical instruments.
Resistance to electrical current of a completely dry wood is equal to that of
phenol formaldehyde. An oven dried wood is a very good electrical insulator. To
some extent air dried wood is the same. Unfortunately electrical resistance of
wood is lowered by increasing the moisture content. The resistance of wood
saturated with water. Static electricity that is dangerous for human health is
not observed in wood unlike metal, plastic and other materials. For this reason
wood is preferred as a healthy material.
Although wood is a light material, its strength is quite high. For instance,
while the tensile strength of wood with 0,6/cm3 specific gravity is 100 N/mm2,
the tensile strength of steel with 7,89/cm3 specific gravity is 500 N/mm2.
Dividing tensile strength by specific gravity gives the breaking length and
quality of material. This figure means the breaking length of the material, when
hung as a result of its own weight. While the breaking length of steel is used
for construction is 5.4 km, chrome mobile steel is 6.8 km, hardened bow steel is
17.5 km, breaking length of spruce wood is 19.8 km, and laminated wood made of
beech is 28.3 km. For this kind of properties, wood and laminated wood is used
in wide-gap constructions like health centers and sport halls.
Wood is a decorative material when considered as an aesthetic material. Each
tree has its own color, design and smell the design of a tree does change
according to the way it is sliced. It is possible to find different wooden
materials according to color and design preference. It can be painted to darker
colors of varnished, and can be given bright or mat touches.
Although wood has oxidation characteristics in some way, it is not the kind
of oxidation seen in metals. Metals get rust, wood doesn’t. For such
characteristics, use of wood is preferred to avoid rust when necessary.
It is easy to repair and maintain wood. While old woods can be renewed by
special touches other materials are highly difficult and costly to maintain and
to repair. Therefore they are usually disposed of.
There are more than 5000 kinds of woods in the world. Their specific gravity,
macroscopic and microscopic structures are different. Accordingly, their
physical, thermal, acoustic, electrical and mechanical properties are also
different. Because of this variety, it is possible to find wood suitable for
needs. For instance, for heat isolation and sound absorption woods in
lightweight are used. Similarly, heavy ones are used for construction purposes.
DISADVANTAGES OF WOOD AND WAYS TO ELIMINATE THEM
There are some disadvantages of wood but they are easy to disregard, and
eliminate as long as the cause is known.
Shrinkage and Swelling of Wood:
Wood is a hygroscopic material. This means that it will adsorb surrounding
condensable vapors and loses moisture to air below the fiber saturation point.
Deterioration of Wood:
The agents causing the deterioration and destruction of wood fall into two
categories: Biotic (biological) and abiotic (non-biological).
Biotic agents include decay and mold fungi, bacteria and insects.
Abiotic agents include sun, wind, water, certain chemicals and fire.
Biotic Deterioration of Wood:
Woods are organic goods. Like any organic good, wood is a nutritional product
for some plants and animals. Humans can not digest cellulose and the other fiber
ingredients of wood, but some fungi and insects can digest it, and use it as a
nutritional product. Insects drill holes and drive lines into wood. Even more
dangerously, fungi cause the wood to decay partially and even completely.
Biological deterioration of wood due to attack by decay fungi, woodboring
insects and marine borers during its processing and in service has technical and
It is necessary to give some short information about fungi agents to take
measures against the wood deterioration.
Physiological requirements of wood destroying and wood inhabiting fungi:
A favorable temperature.
The temperature must be 25-30°C for optimum growth of most wood rotting
fungi. But some of them can tolerate temperature between 0-45°C.
An adequate supply of oxygen
Oxygen is essential for the growth of fungi. In the absence of oxygen no
fungi will grow. It is well known that storage of wood under water will protect
them against attacks by fungi.
Generally wood will not be attacked by the common fungi at moisture contents
below the fiber saturation point. The fiber saturation point (FSP) for different
wood lies between 20 to 35% but 30% is accepted generally.
It is recommended that wood in service must have a moisture content at least
3% less than FSP to provide desirable safety against fungi.
Wood is an organic compound and consists of 50% carbon. That means that wood
is a very suitable nutrient for fungi because fungi derive their energy from
oxidation of organic compounds. Decay fungi wood rotters can use polysaccharides
while stain fungi evidently require simple forms such as soluble carbohydrates,
proteins and other substances present in the parenchyma cell of sapwood.
Additionally, the presence of nitrogen in wood is necessary for the growth of
fungi in wood.
Insects are only second to decay fungi in the economic loss they cause to
lumber and wood in service. Insects can be separated into four categories:
Termites, powderpost beetles, carpenter ants and marine borers.
There are two types of termites: Subterranean termites damage wood that is
untreated, moist, in direct contact with standing water, soil, other sources of
Dry wood termites attack and inhabit wood that has been dried to moisture
contents as low as 5 to 10%. The damage by dry wood termites is less than
Powderpost beetles attack hardwood and softwood. At risk is well seasoned
wood as well as freshly harvested and undried wood.
Carpenter ants do not feed on wood. They tunnel through the wood and create
shelter. They attack most often wood in ground contact or wood that is
They cause damage primarily to unpainted wood by creating large tunnel in
order to lay eggs.
They attack and can rapidly destroy wood in salt water and brackish water.
Minimizing the Problems of Wood:
Most of the commonly employed strategies for protecting wood involve drying,
coating and or impregnation.
Careful selection of wood
Some species have naturally decay resistant heartwood. Such species include
sweet chestnut (Castanea sative Mill.), oak (Quercus spp.), juniper (Juniperus
spp.). Sapwood is never naturally durable species has little or no decay
resistance and must be treated if long-term durability is desired.
Coating provides protection to wood used both indoors and outdoors. Coating
prevents rapid uptake and loss of moisture and reduces shrinking and swelling
that can lead to surface cracking and other problems. But coating does not
totally prevent changes in moisture content. Coating slows, but does not halts
moisture level. Coating with solid color or pigmented stains protects wood
against ultraviolet rays.
The addition of fungicides to coating provides some protection against
development of decay and mold fungi.
Deteriorating paint film actually increases the decay hazard. Cracked paint
allows moisture to come into contact with wood surface, and poses a barrier to
rapid and complete redrying.
Generally wood will not be attacked by the common fungi at moisture content
below the fiber saturation point (FSP). FSP for different wood lie between
20-35%, but 30% is accepted generally: Fungi can not attack wood used indoor and
in heated rooms, since the equilibrium moisture content (EMC) is much more below
than FSP. e.g. 6%
If wood is soaked in water, wood absorbs water and is saturated with it.
Finally there will be no more oxygen in wood. In this situation fungi can not
grow in them. This is the main reason why woods are kept in water for a while.
Besides underwater constructions, it is impossible to use woods completely wet;
so when they are used out of water, they have to be completely dried out to EMC
in order to protect them against fungi attack. In heated rooms, where the EMC
lie between 5-10%, fungi can not survive on them.
One of the most effective ways to prevent degradation of wood is to
thoroughly dry it and keep it dry. The last case is very important since even
wood that has been kiln dried will readily regain moisture if placed in a humid
Wood can be dried in air or in some type of dry kiln. Air drying alone is not
sufficient for wood items which are used in heated rooms. Therefore kiln drying
is necessary. Kiln drying has many advantages: One of them is the killing of
staining or wood destroying fungi or insects that may be attack the wood and
lower its grade.
Wood that will be used indoor need only be dried to provide for long term
protection against rot.
Treating With Wood Preservatives
We can prevent decaying of wood by treating it with wood preservatives. But
some of the wood preservatives may harm humans and other creatures. For this
reason if wood is used outdoor in situations where it is often wet or in close
proximitly to liquid water, then wood must be treated with wood preserving
chemicals to achieve long term durability.
Wood preservatives are divided into two groups: Waterborne and oilborne
About %75 of wood that is commercially treated today is treated with
waterborne salts, and CCA is the compound used in treating for the greatest
volume of wood.
Only creosote and pentachlorophenol are effective protecting wood in direct
ground contact. These are also the only two oilborne preservatives that provide
general protection against decay causing fungi, termites, marine borer and other
Oil based or oilborne preservatives are generally used for treating of wood
used outdoors in industrial applications; such as ties, piling and poles.
In a serious situation, wood is treated with waterborne preservatives for
example chromated copper arsenate and, after thorough seasoning, is retreated
Wood in service must be periodically retreated by brushing or a variety of
Retreatment of wood window frames, door frames and wood timber and beams is
sometimes carried out by drilling holes in areas where decay has begun and
filling these holes with a suitable treating compound. Treating compound in the
form of solid rods are mostly preferred since it provides a slow release of
Retreatment of wood used in ground contact must be realized by application of
pastes and wrapping with preservative impregnate bandages.
Abiotic Deterioration of wood:
Another disadvantage of wood is that it easily catches fire. Wood consists of
organic compounds which are composed mainly of carbon and hydrogen. They can
combine with oxygen and burns. Because of these properties, wood is classified
as a combustible material.
If the temperature of a inflammable gas is between 225°-260°C, it burns with
a touch of flame. After the withdrawal of flame it will stop burning. If the
temperature increases to 250°-270°C, it burns with a touch of flame and goes on
to burn without a flame. If the temperature increases to 330°-520°C, wood begins
to burn spontaneously. Chemical materials, especially extractives in woods
structure cause the burning point to change. For example, a resinous piece of
pinewood can catch fire in lower temperatures. In addition to this, specific
gravity and surface mass (m2/kg) affect the duration of flame. Wood burns harder
when the specific gravity and surface mass and moisture content increase, and
Using thick wood as a structure element is another way of extension of
burning point. Outer surface burns and turns into charcoal. Charcoal, which
forms on the surface of wood as it burns is a very effective heat insulator.
Therefore large timbers burn very slowly. In addition to this, wood is very good
heat insulator too. The outer surface of the wood is 1000°C and the interior
part is still 40°C when a piece of thick wood is burning. For this reason,
buildings with thick structure elements such as beams and columns do not
collapse easily on fire. On the other hand, in steel constructions, as heat
increases, steel faces deformation, and their resistance decreases and
collapses, where wood is used preventive measures must be taken for safety
against fire. In this case wood is not a dangerous material.
It is impossible to make wood noncombustible like inorganic materials. In
order to prevent potential dangers, wood can be processed in some fire
Fire retardants may be divided into two categories: Coating and
chemicals-water soluble salts-that are impregnated into the wood structure.
Coatings are used to reduce the formation of volatile, flammable gases by
promoting rapid decomposition of the wood surface to charcoal and water. They
also protect wood surface against high temperature water soluble salts e.g.
diammonium phosphate, ammonium tetraborate, sodium acetate, alkali silicates,
borax are used against fire hazards in wood. Wood can be impregnated by these
chemicals. This type of process can contribute to the increase of the burning
point and retard spread and penetration of flame.
Fire retardants only reduce the flammability of wood and slow or eliminate
progressive combustion. They do not prevent burning totally in the presence of an
external source of fire. In this case, wood does not go on burning once an
external source of flames is removed.
Prof. Dr. Ramazan ÖZEN
President, Zonguldak Karaelmas University