Solid wood construction

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Outer wall made of solid wood

The solid wood construction describes a construction method in wood construction and differs from other wood construction methods such as the skeleton construction or the timber frame construction by its consistently massive element structure.

Solid wood construction elements are produced as wall, roof and ceiling elements. In terms of construction, it is glued laminated timber or cross laminated timber . The individual board layers can be glued together or connected with wooden dowels or wire pins . Thanks to the large, usually prefabricated wall elements, short construction times are achieved and costs are reduced. The shell for a single-family house can be erected in around three days and closed in a weatherproof manner.

Building physical characteristics

Landsberg Castle surrounded by forest

CO ₂ storage

For more than 250 years, wood has been obtained from sustainable forestry in Germany, which means that no more wood is harvested than can grow back in the same period. With more than 3.4 billion m³, Germany has the largest usable wood stocks in Europe. If this wood is used specifically and used in the form of building materials in walls, ceilings, roofs and insulation over the long term, it serves as a CO ₂ store and thus has a positive effect on our climate. If wood does not rot but is used over the long term, it removes carbon dioxide from the atmosphere. In an average single-family house in solid wood construction with around 160 m² of usable space, around 90 m³ of wood are used. This amount of wood stores an amount of 74 t of CO ₂ over the life of the house , which corresponds to the amount emitted by around 52 average cars per year. Wood is the only building material that has a lasting positive effect on our climate.

Moisture protection

Canale in Venice

Solid wood construction uses the advantages of its large wood mass without having to accept the disadvantages of shrinkage and the release of building moisture, for example .

Wood has the property of swelling and shrinking mainly in width. The cross-laminated timber structure ensures that the elements are dimensionally stable. Possible damage caused by slow, constant and therefore often unnoticed water ingress at seepage points of water connections or pipes is a major problem with all building materials. If water comes out of damaged water pipes for months or even years before this is noticed, the renovation of the affected components is usually expensive and laborious. Since wood begins to be too modern in the event of permanent soaking and thus naturally loses its strength and structure, this represents a serious damage pattern. Permanent moisture penetration is used if the wood moisture content is more than 25% over a period of more than twelve months.

Due to the high structural strength of solid wood construction elements, damaged areas can be cut out and replaced with new components. The millimeter-accurate production with CNC-controlled systems that is common today makes this possible. There is no risk of structural damage from fungus formation as a result of the formation of condensation or condensation. Air that is not completely saturated with moisture has a relative humidity of less than 100% and can - if the temperature remains unchanged - absorb further water vapor. If the temperature decreases, the absorption capacity of the air for water vapor also decreases, that is, the relative humidity increases. At the dew point, a relative humidity of 100% is reached, and condensation occurs. Due to the hygroscopic properties of the wood, the dew point is normally always outside the structure. This means that the moisture absorbed by the wood means that the air diffusing through the wall is so dry that water can no longer knock out. If, however, a leak is so large that condensation occurs within the wall structure, the surrounding wood mass is large enough to deal with the moisture that occurs.

A volume flow of 228 m³ / h air would be necessary to achieve a wood moisture content at which mold can form.

Wet areas are among the most damaging areas in all areas of building construction, regardless of the type of construction. Damage can occur in the shower area in particular, which is extremely costly to repair, but which could have been avoided with proper planning and execution. The DIN 68 800 series of standards states: " For wooden components that are directly ... stressed by the effects of moisture in the installed state, a surface coating (coating) is not a sufficient measure ." A corresponding preventive measure may therefore be necessary to prevent fungal growth due to excessive wood moisture Treatment with suitable wood preservatives is recommended. However, to avoid the use of chemicals in your own four walls, simple, preventive structural measures should be taken. Here it says: "... wooden components in wet areas of rooms with a normal living climate can be assigned to hazard class GK 0 if an unsuitable moisture load on the wooden parts is permanently prevented, for example through waterproof surfaces, also in the area of ​​penetrations and connections ...". These waterproof surfaces can be achieved, for example, by cladding with plasterboard with a tile covering using sealants for gluing and grouting. Regardless of this, protective measures against "accidents" with washing machines or bathtubs must be provided for floors. This means that the undersides of the ceiling should be made diffusion-open, no moisture-storing bulk materials should be used in the ceiling cross-section, and a floor covering structure that is as waterproof as possible should be provided.

Soundproofing

As already described in other areas, the resident of a house not only places demands on the building that have an impact on the fabric of the building, but also has additional needs. One of them is sound insulation . Protection against external noise and internal noise sources has become an essential part of our quality of life . This development was recognized at an early stage, particularly in timber construction, and was incorporated into the development of high-performance building materials. If the standards do not yet place very high demands on sound insulation for single-family houses, this is different for multi-family houses and commercial buildings. Due to the high, acoustically inert wood mass, multilayer structures and different wall thicknesses and cladding, the increased requirements, for example in school buildings, can now be met with little effort. When it comes to soundproofing against outside noise, it is not only the good sound insulation of the wall construction itself that is decisive, the interaction between the wall and the windows in the respective areas also determine the quality of the construction. As with all single-material building materials, when connecting ceiling components made of solid wood to equally solid wooden walls, great care must be taken to ensure that the following floor structure is "floating", i.e. decoupled. Sound is transmitted from the floors via the ceiling into the wall construction and the resulting acoustic amplification of the impact noise avoided.

heat protection

The high bulk density of wood ensures a long phase shift . In civil engineering, phase shift describes the period between the occurrence of the highest temperature on the outer surface of a component and the reaching of the highest temperature on its inner surface. This is especially important for thermal insulation in summer, since with a long phase shift it remains cool inside the house even at high outside temperatures. Obviously, this principle works the other way around at low outside temperatures. The U-value (formerly K-value) used to calculate the heating energy demand of a house only states how much heat is permanently lost, but not how long it takes for these losses to occur.

The phase shift is calculated from:

1. Bulk density
2. Specific heat storage capacity
3. Temperature penetration coefficient
4. Thermal conductivity

Buildings made of solid wooden elements with their high bulk density and high specific heat storage capacity, but with a low temperature penetration coefficient and low thermal conductivity and the resulting long phase shift, only have a low heating energy requirement.

Fire protection

Contrary to popular belief, a solid wooden element can withstand fire for a very long time. The wood used contains up to 15% water, which must first evaporate in the event of a fire (one ton of wood corresponds to 150 liters of water). When burning, the top layer of wood charred and acts like a kind of protective coat. Oxygen can no longer penetrate the wood and the burn slows down considerably. Due to the low thermal conductivity of wood, there is also no risk of spontaneous combustion, e.g. wallpaper or curtains on the other side of the wall. The fire resistance for load-bearing and space-enclosing components, walls and ceilings is currently specified or examined in two different formats in Germany and Europe:

Germany: for example F 90 B; where F = fire resistance duration 90 = tested minimum duration until the construction collapses in the event of fire. B = Flammable Europe: In Europe, the assessment of fire resistance is somewhat different.

Instead of “fire resistance of components” one has to get used to the term “fire resistance of building products”, and thus to much more and new codes and much more time spans than before. The possible time periods are 15, 20, 30, 45, 60, 90, 120, 180, 240, 360 minutes. If criteria are combined, the specified "performance time" corresponds to the criterion with the shortest duration. for load-bearing components:

REI [performance time] Minimum time during which all criteria (load-bearing capacity, room closure and thermal insulation) are met; RE [performance time] Minimum time during which the two criteria (load-bearing capacity and space closure) are met; R [performance time] Minimum time during which the load-bearing capacity criterion is met.

Indoor climate

Solid wood construction systems are usually constructed so that they are permeable to diffusion and can therefore absorb, store and also release vaporous moisture. This property has a balancing effect on the room air humidity, so that there is a seasonally dependent, relatively even air humidity in the house .

This property is particularly useful in humid weather or when there are many people in a room. Usually a wooden house is completely built with natural building materials that can easily reach room temperature. This means that there is no unpleasant cold radiation, which can also lead to drafts.

The handling of volatile organic compounds (VOC) is an important issue, especially for the increasing number of allergy sufferers. We spend more than 90% of our time indoors. The sensitivity of many people to possible or suspected impairment of the living environment by pollutants is correspondingly high.

In addition to furniture, floor coverings and the like, building materials and finishing materials also emit various substances into the indoor air. Terpenes and formaldehyde, which occur naturally as a metabolic product of the tree in low concentrations in all wooden components, are the substances most examined here.

Terpenes are organic compounds that occur naturally in flowers, leaves, fruits, bark and roots and in the essential oils that can be extracted from them.

Important terpenes are, for example, delta-3-carene and limonene. Limonene occurs in the peel of citrus fruits and is used as a citrus scent substitute in many kitchen products (detergents and dishwashing detergents, etc.). Often products with terpenes are declared as "organic" paints, varnishes, oils and waxes because of their natural occurrence and thus suggest a particularly good environmental compatibility. However, this is wrong. Terpenes are a serious pollutant in living areas. However, the concentrations of terpenes usually found indoors are orders of magnitude below the level at which acute toxic effects are to be feared. But they can also be used as environmentally friendly insecticides by acting as pheromones to lure insects into traps.

With standard concentrations of less than 0.03 ppm (parts per million), however, the values ​​are well below the limit values ​​of 0.1 ppm, which are regarded as harmless to health.

flexibility

Due to the CNC-controlled production, the components have a high accuracy of fit and allow an individual composition of the floor plan. The facade can be made of wood, plaster, clinker or other materials.

Due to the high structural strength, it is possible to add window or door openings later, often years later. In addition, multi-storey buildings can be carried out without the support of reinforced concrete elements. In Germany, the construction heights for wooden buildings are usually limited to six full storeys, in other parts of the world, such as London, it is permissible to erect buildings with up to nine full storeys.

Pests

Larva of the shotgun

Insects are important links in nature's nutrient cycle. They keep the earth from suffocating on the abundant growing plant material. Some insect species are already trying to get close to living trees, especially the "defenseless" leaves and needles. A healthy tree produces antibodies in various forms. Food poisons (e.g. tannin, robinin) or volatile odorous substances (e.g. essential oils, terpenes) that keep the insects away and spoil their taste. As soon as a tree has a bark damage, is ailing or felled, things really get going: little animals come from all sides and lay their eggs under the bark and in the wood. The hatching larvae then eat their way through the wood and sometimes only reappear when the wood is processed. If fresh wood insects are now still contained in the wood after processing the felled wood, these are normally killed during the drying process. When the wood is heated to around 70 ° C, the structure of the protein contained in the wood is changed and is no longer usable for pests. Any further development on the wood used can therefore be ruled out. In construction, it is mainly the built-in wood that is of interest, i.e. the dry wood and its pests. Fresh wood insects are bound to fresh wood. This simple truth answers one of the most frequently asked questions: Are fresh wood insects in firewood a threat to the wood used in the house? As a rule: no!

The classic representatives of dry wood insects in our regions are the wood worm and the wood tick . The larva of the woodworm needs a minimum wood humidity of more than 10% and prefers cooler places - therefore it rarely occurs in heated rooms. Critical areas are permanently damp rooms or where floor cool / damp can occur. The construction method without thermal bridges and the good insulation properties of solid wooden structures generally do not allow this. The development of the larvae is not only dependent on the moisture content of the wood, but also on the protein content, as in the house buck. Due to the structural change in the protein when the wood dries, it can no longer be used by dry wood pests, and an infestation by the woodworm is unlikely or even impossible.

The female billy-goats, which are in and of themselves very happy to lay, lay their eggs only in crevices, for example dry cracks in wood, of a certain width. For artificial columns with parallel walls, widths of 0.3–0.6 cm are almost exclusively chosen. The time it takes for the larva to develop depends heavily on various factors (such as protein content, moisture, temperature, type of wood) and is around 4-18 years. The house goat larva requires a minimum wood moisture content of approx. 12%, with the ideal development moisture being approx. 30%. That is why an infestation by house buck larvae hardly ever occurs in the exposed wooden components of heated rooms. Due to the gaps that can occur in cross-laminated timber of this size, and the necessary moisture development, which is not achieved according to the provisions of DIN 1072 , the risk of infestation by the house buck is practically excluded.

A threat somewhat different kind are involuntarily on vacation souvenirs or even from Asia imported furniture entrained insects. Insects travel aimlessly and rampantly around the world - the globalized economy and mass tourism make it possible! In order to be able to continue living in someone else's home, the wood destroyers have to eat the wood. Since these little animals are very busy, damage done quickly catches the eye and can be fought. The forcibly brought in are not really at home in our latitudes. Usually it is, for example, the climate or the opposite seasons in the northern and southern hemispheres that do not fit. That is why the risk to timber construction is very low from this side as well.

Life cycle assessments

The good insulating effect of wood is due to the high proportion of air in the intercellular tissue. Timber houses therefore require less heating energy in the winter half-year, which reduces CO ₂ emissions and heating costs. In summer, the interiors stay cool even in high temperatures without air conditioning . The requirements of the Energy Saving Ordinance (EnEV) can therefore be complied with. In some cases, the building material exceeds the applicable building guidelines. It is therefore suitable for the construction of low-energy or passive houses . Wood also saves a lot of energy when modernizing existing buildings. Combined with special glazing, heat losses and thus energy consumption can be reduced to a large extent.

Every building material has a different energetic behavior. In the energy calculation according to EnEV, however, there is no differentiation between glass, concrete, brick or wood. The heating energy requirement is not only calculated according to the U-value , the phase shift or surface structure also play an important role here.

The energy balance of a house results in very different values ​​due to the material, manufacturing processes and type of construction, which will play an increasingly important role in future closer consideration not only of the "consumption", but of the energy balance over the entire life of a building.

As a renewable raw material, wood is a building material that binds carbon dioxide and consumes little energy to provide it. Around 90 cubic meters of wood are used in an average single-family home. This amount relieves the environment of around 125 tons of carbon dioxide. To produce one m³ of solid wood elements, including prefabrication values, 1,529.8 MJ (425 kWh) are required, for fired bricks the value is 5,600 MJ (1,555 kWh). Approx. 676 MJ (188 kWh) are required to produce one m³ of soft wood fiber insulation, and 2,700 MJ (750 kWh) for plasterboard . This means that the complete construction of a massive wooden house, including wood extraction, requires around 38,000 kWh of energy. The same building in conventional solid construction requires around 170,000 kWh.

Dismantling or recycling of wooden structures is relatively easy. A large proportion of the waste generated can be thermally recycled.

lifespan

Pharmacy in Dinan / Brittany

With a share of almost 15% in residential construction , timber construction is significantly underrepresented in Germany compared to that in other nations in Europe. Almost half of these buildings, namely 45%, are in the traditional timber construction regions of Bavaria and Baden-Württemberg. So far, only a few towns and municipalities can boast of municipal buildings made of wood. In many cases, the architectural possibilities and economic advantages are not known to the building authorities responsible for urban development . Through quality improvements in all areas, the lifespan of wooden buildings has been raised to the level of solid buildings in conventional design in recent years. The technical service life, i.e. the period in which a building can be used economically with normal maintenance, is 80 to 100 years according to today's standards. The total useful life , i.e. the period from construction to demolition of a building, can be several centuries with appropriate maintenance. Correspondingly old temple buildings, even in the earthquake regions of Japan, or half-timbered buildings in our historic old towns prove this. With regard to the valuation of buildings and their insurance, wooden buildings from a construction date of 1985 onwards are equated with conventional solid buildings.

Good structural wood protection is the life insurance of every wooden structure. The further development of technical processes in the processing of wood and new findings in terms of construction have contributed to the fact that chemical treatment of the outer facade can largely be dispensed with.

Value retention

The building materials and processes predominantly used in the construction industry are generally of relatively high quality due to the high technical requirements imposed by the standards . A differentiation with regard to the effectiveness and ecological classification of these building materials is nevertheless appropriate.

A sometimes considerable price difference between a prefabricated house from the hardware store and the manual production in carpentry is quite justified on closer inspection of the individual components. The massive timber construction can keep up with the "normal" construction methods in terms of price due to the millimeter-precise production using CNC-controlled beam machines and the simple construction with a few different materials without quality restrictions.

Since massive wooden structures can be converted or dismantled just as easily as they were once built and due to the almost continuous use of natural materials in the walls and insulation - combined with the good reusability of these materials - it has a significantly higher value retention than when using synthetic insulation materials to be expected. This is now recognized by most banks and insurance companies.

literature

• Information service wood (Hrsg.): Timber construction manual. ( Information online )
• H. Frey, H. August: Structural engineering - specialist knowledge of construction . Europa Verlag, Haan-Gruiten 2003, ISBN 3-8085-4460-0 , p. 394 .

Web links

• Primary energy consumption. ( Memento from August 30, 2009 in the Internet Archive ) of wood building materials compared to other solid building materials
• Magazine of the Federal Guild of Timber Construction in Austria
• Building supervision test certificate for a solid wood wall ( Memento from July 14, 2010 in the Internet Archive ) (PDF file; 0.9 MB)
• Forest and Wood Products Research and Development Corporation (PDF file; 19.5 MB)
• Appraisal of wooden houses

Individual evidence

1. ↑ Bernhard Leiße: Wooden components properly protected. DRW-Verlag, 2002, ISBN 3-87181-356-7 , p. 25.
2. ↑ Bernhard Leiße: Wooden components properly protected. 2002, p. 43.
3. ↑ Bernhard Leiße: Wooden components properly protected. 2002, p. 44 ff.
4. ↑ S. Winter, D. Kehl: Investigation to objectify the evaluation of the market value of buildings in timber construction in comparison to other construction methods . Final report. 1st edition. Leipzig, 2002.
5. ↑ S. Winter, D. Kehl: Timber construction manual, information service wood, R3 / T1 / F2, timber houses - value retention and durability. Ed .: DGfH Innovations- und Service GmbH, Munich and Holzabsatzfonds, Bonn 2002, OCLC 177238929 .
6. ↑ A. Ohler: Influence of the construction method on the evaluation of residential buildings. Buxtehude 1998.