Building timber is
needed above all to erect a truss, i.e. a load-bearing roof structure, unless
we have decided on a skeleton house, all of which is wooden. Whether we want to build a roof, the
whole house or just a gazebo, we should choose lumber of the best quality.
Wooden skeleton of the
building
In addition to the
skeletal house and the above-mentioned roof truss, construction wood can be
used for the construction of property fences, internal stairs, a balcony or
terrace, and a whole variety of garden buildings - gazebos, cells, worlds.
It is considered good
construction timber from conifers - mainly pine. The most valuable is the larch,
however, due to the high price, it is used less frequently. In the mountainous surroundings pine
often replace fir and spruce. Deciduous
trees are made of constructions that are to be not only load-bearing, but also
nice. They are therefore usually
used inside buildings, and stairs, mezzanines or other exposed structures are
made of them, not to mention strictly finishing - floors, wood-paneling or window sills. For internal constructions we buy
mostly ash, but also oak or elm.
The quality of wood
The wood selected for
structural purposes must be dry. Its
moisture should not exceed 20% by weight. The
moisture level is measured with a moisture meter. If wet wood were to be used for
construction, it would soon become numerous deformations, because it would dry
up in improper conditions. In
sawmills, the wood is dried in the open air. Lumber
elements are laid on a carefully leveled substrate. There are spacers between its
individual layers. The elements
are also apart from each other.Everything so that the air could blow them from
every side. This process takes
many months. It dries wood faster
in chamber dryers. These are
buildings where the air temperature is raised to 75 ° C. In such conditions, drying takes
instantaneously, because only a few hours. In
addition, high temperature kills all microorganisms in the wood. As a result, it becomes resistant to
insects or fungi. The moisture
content of dried cell wood is not more than 16%.
The lumber should have
thick wood grains and can not have any defects. Such are considered primarily
numerous, deep and loosely connected with wood knots, which weaken the strength
of timber. The worst are knots
passing through the entire thickness of the element. In individual elements there can also
be too many stoppers, i.e. places where the bark was deep enough that it did
not remove it. Wood also
disqualifies deep cracks, twists or traces of the presence of the domestic
fungus (strange colorful spots, growths, cords). They are not dangerous discolorations
called blue stain or survival.
Wood class
Construction timber in a
sawmill is sorted by class. Class
IV wood is practically free of defects. The
lower the class, the more shortcomings. The
class is often marked with a color. I
- blue, II - green, III - red and the highest - IV - yellow. The second class of lumber is already
of sufficient quality.
There are also classes
characterizing the mechanical strength of timber at its moisture content of
12%: C18, C22, C27, C30, C35 and C40. The
digit informs about the bending strength. The
higher the class, the more durable the wood. For
building applications, this is suitable for class not less than C24.
Machining type
Construction timber is
created in a sawmill. There,
beams, logs, squares or boards are cut from the trunks. They have equal edges and are devoid
of bark. Such elements are
generally referred to as edged timber, unlike unedged timber, which has only
two surfaces cut, and the other two have bark. Precise machining is ensured by
planing. It is a process during
which the elements gain a smooth surface, and their edges are sometimes
slightly sheared, i.e. beveled. Lumber
prepared in this way is more resistant to fire than ordinary. It looks nicer, too. Unfortunately, it costs more. In the sawmill, we can also order
cutting elements to measure, based on the design.
Impregnation
It is a process of
chemical protection of wood, which is supposed to prevent attack by pests and
fungi, home and mold.Impregnating substances can also reduce the flammability
of wood. The most effective
method of impregnation is pressure impregnation. Normal lumber is impregnated. This four-sided planed and
chamber-dried is itself sufficiently immunized.
Construction wood from
the factory
In addition to typical
solid structural wood, the following elements are available:
- from KVH sawn timber -
these are elements made of wood dried in a chamber and four-sided planed in the
form of beams joined longitudinally by finger-joints. It thus arises from several shorter
elements. Thanks to such a
construction they have better torsional strength and can have larger spans;
- made of glued wood -
it is made of four-sided planed and chamber-dry timber. Elements are made by gluing wooden
strips together. The wood thus
made is resistant to moisture and can reach very large spans. It easily bends, so arched elements
are also created. There is no
tendency to deform. Glued wood is
expensive and for this reason rarely used in single-family housing;
- prefabricated elements
- these are beams with I-section. Their
narrow and high web is made of plywood or fiberboard with a small thickness. At the bottom and at the top there are
solid wood feet that provide adequate stiffness. These beams are light (3-6 kg / m), and at the same
time very durable.
