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Cross-laminated timber: a versatile material
Cross-laminated timber: a versatile material

Video: Cross-laminated timber: a versatile material

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Video: What is Cross Laminated Timber (CLT)? 2023, January

Cross-laminated timber is particularly strong, dimensionally stable and dimensionally stable. Prefabricated elements for exterior and interior walls, ceilings and roofs can be quickly assembled on site.

Wooden materials consist of layers, chips or fibers of the same or different thickness or size, they are glued or pressed with binders. This is why wood-based materials are more evenly constructed than solid wood and more stable, making them suitable for particularly large-scale wooden structures. If individual layers of veneer or lamella are glued into panels, layered materials are created. The most important for builders and renovators are plywood, plywood and cross-laminated timber.

  • Laminated wood: The grain of all wood layers in glulam points in the same direction, in the longitudinal direction the material is particularly resistant to bending and tensile.
  • Plywood: The layers are laid one on top of the other along the wood fiber direction and rotated by 90 degrees - experts call them cross-glued or cross-glued (KLH - cross-laminated timber). The fibers always run parallel on the visible surfaces, resulting in an odd number of veneer layers. Cross gluing locks the individual layers against each other and prevents them from “working”. Plywood is particularly dimensionally stable.
  • Cross-laminated timber is multi-layered and made entirely of solid wood. It is a solid, prefabricated part made of wood that insulates heat and can simultaneously carry loads, is fire-proof and good sound-absorbing, can be installed dry quickly and has a positive impact on people's well-being. The flat, seamless surfaces and the special structure guarantee precisely defined building physics, fire technology and mechanical properties. Cross-laminated timber can be used universally and can be easily combined with other materials. The surfaces can be left natural or color treated. The board layers lie flat on top of each other, which is a significant difference to the glulam mentioned above.

Cross-laminated timber is a solid prefabricated part made of wood that insulates heat and can also carry loads.

Photo: Brüninghoff

Cross-laminated timber: simple and proven

If you want to move into your own home quickly, you save on rent - unfinished buildings made of prefabricated solid wood elements in wooden panel construction are ready within a few days.

Components made from only one material are called monolithic, the cross-laminated timber elements consist of 99.4 percent wood and 0.6 percent adhesive. Many planners prefer monolithic components over multi-layered constructions, foils and complex connection details - simply planned and built houses can also be easily checked.

The solid components made of cross-laminated timber are made in strips, their dimensions are used for economical constructions - 125 centimeters wide to 24 meters long, and the thicknesses are between 60 to 280 millimeters. The wood is dried to twelve percent (+/- 2) residual moisture. Cross-laminated timber is made from Central European spruce wood, the surfaces are planed on both sides, optionally sanded on one side, each smoothly and seamlessly glued. For the top layers in visible quality, the wood types spruce, larch, silver fir, Douglas fir and Swiss stone pine are available in the qualities "residential view" on one or both sides and "industry" on both sides. The adhesive is formaldehyde-free, transparent, weather-resistant and open to diffusion. All longitudinal edges are chamfered about three millimeters and have standard profiles such as rebate or groove on both sides. The cross laminated timber strips have the European Technical Approval ETA, CE marking and the German building inspectorate approval.

Areas of application for cross laminated timber

Basement walls, exterior walls, interior walls and partitions can be built from cross-laminated timber. The wall elements meet all requirements of statics, stiffening, fire protection and building physics safely and solidly. If the wall elements are used vertically, they are installed at floor level or in one piece over several floors - each individual element acts as a stiffening disc. Installed horizontally, the production length of 24 meters can be used economically. The combination of vertical elements as supports with horizontal elements as stiffening panes optimizes the statics.

Natural heat protection through cross-laminated timber

The Energy Saving Ordinance (EnEV) requires effective thermal insulation and absolute windproofness for new buildings. Houses made of solid wooden components meet all requirements - without building foils.

Each longitudinal layer of cross-laminated timber consists of glued single-layer panels (BSP - cross-laminated timber panel), the elements have smooth, seamless surfaces on both sides and a completely dense and compact cross-section. In this way, low-energy and passive houses can also be built, the constructions achieve all the required thermal insulation values ​​of the Energy Saving Ordinance and are windproof as required - provided that they are properly executed.

Build without foils

Basically, cross-laminated timber constructions are carried out without vapor barriers and wind brakes; Walls, ceilings and roof are open to diffusion, including the adhesive joints. Experiments by the adhesive manufacturer prove that the usual adhesive joint has the same diffusion resistance as a 35 millimeter thick spruce board. The entire cross-laminated timber contributes with full thickness to the heat protection. Both surfaces are smooth, seamless and closed; warm air cannot penetrate into the interior of the element and thus into colder layers.


Cross-laminated timber is fire-proof, good soundproofing and can be dried and installed quickly.

Photo: Brüninghoff

Solid walls store the heat

Walls, floors and ceilings made of solid wood store heat and release it into the air when needed - this saves heating costs. The U-value of a component can be measured in a regulated heating box in accordance with EN ISO 8990. These are two boxes that are separated by a wall made of light insulation. A square meter element is built into this wall. Room one is constantly heated to about 20 degrees Celsius, room two is constantly cooled to about zero degrees Celsius. Heat flows from warm to cold, from room one to room two through the wall. The U-value is calculated from this heat flow - as soon as it has leveled off at a constant value.

It takes about six days for almost constant heat flow (loss) through a 21.1 centimeter thick wall made of cross-laminated timber - only from this point on the U-value may be determined, it does not take heat storage into account. However, the experiment shows that a large part of the heating energy for room one is stored on the warm side of the wall and is only slowly transported outside. Whoever chooses the building material for his house should not only ask how effectively the material insulates heat. But also how well the building material stores heat.

Low energy consumption thanks to cross-laminated timber

The required wall thickness is calculated according to the prescribed minimum U-value, depending on the location in Europe, either the standardized lambda value for wood of 0.13 W / mK (watts per meter x Kelvin) can be used for its calculation, or partially recognized and tested value of cross laminated timber of 0.10 W / mK. Only windows and doors with good U-values ​​are built into the walls, the roof is usually made of elements around ten centimeters thick - for summer thermal insulation with sufficiently high thermal insulation (U-values ​​below 0.1 W / mK). The heating load or the primary energy requirement is determined from the average U-value of all external components; In this way, cross-laminated timber structures achieve the desired low-energy standard. Experience shows that the calculated energy requirement is often higher than the actual one - especially after installing radiant heaters such as tiled stoves or wall heaters.

Windproof building envelope

Where there is no wind whistling through cracks, noise from outside is also blocked. A clever construction prevents sound transmission from one room to another.

The so-called blower door test is used to check the airtightness of a building. The measurement takes four to five hours. A fan in the door or window creates a pressure difference between inside and outside, so a flow meter locates leaks, i.e. leaks. One measures the volume flow, which is necessary for 50 Pa differential pressure - with the measure Pascal = Pa one designates the pressure on a square meter surface. The differential pressure of 50 Pa is divided by the air volume of the building examined. The so-called n50 value is obtained, which is used internationally for assessing the airtightness of buildings.

An n50 value of three per hour means: at 50 Pa differential pressure, the air volume in the building is exchanged three times per hour. The Passive House Institute Darmstadt specifies an n50 value of up to 0.6 per hour as a quality requirement for a passive house, the blower door measurement of a cross-laminated timber house resulted in an n50 value of 0.7.


Basement walls, exterior walls, interior walls and partitions can be built from cross-laminated timber.

Photo: Brüninghoff

Effective soundproofing with cross-laminated timber

Two-storey test buildings were built next to each other to measure the sound transmission, the values ​​for:

  • Bodyshell (connections and flank transmission),
  • Visible quality ceilings (raw and with floor structure),
  • Interior walls with visible quality on one and both sides.

    The test facility was built according to the recommended guidelines for buildings made of cross-laminated timber. Properly planned and carefully executed constructions meet all requirements for sound insulation.

On a cross-laminated timber with five layers or more, two layers can be removed for installation work, for example, a locally three-layer cross-laminated timber remains with surfaces closed on both sides - longitudinal sound lines in the element via open joints or cavities, so-called channel effects, are hardly possible.

Seamless components

The EN ISO 7730 standard defines the comfort temperature in a room as the average of the air and surface temperature - the "warm" building material wood actively contributes to the well-being of the residents.

Cross-laminated timber slows down steam, but does not block it. Each individual longitudinal layer consists of a glued single-layer board, as a rule construction is carried out without vapor-retarding or vapor-barrier foils - this means price advantages and environmental protection. Both surfaces of the cross laminated timber are smooth, seamless and closed, moisture from outside cannot find its way into the element. As a rule, if the element joints are carried out correctly, partial sealing (except in the joint area) or the entire surface can be dispensed with moisture sealing sheets. The moisture only penetrates a few millimeters into the surface of the element and quickly diffuses out.

Constant room humidity thanks to cross-laminated timber

Many people find fluctuations in room temperature and room humidity uncomfortable. If it quickly gets cold in a room when the heating switches off, or if it gets unbearably warm when it gets hot outside, then one speaks of a barrack climate. Cross-laminated timber protects against such processes - in summer and winter.

On the inside of the house, the wood allows the room air water vapor to move through external components and absorbs excess without damage. This sorption property promotes a comfortable and balanced living climate. The material reacts to changes in the indoor climate and dampens peak levels of indoor air humidity. For example, if the relative humidity in a room at 20 degrees Celsius increases from 55 to 65 percent, one cubic meter of cross-laminated timber stores around seven liters of water. If the relative humidity changes from 80 percent to 55 percent, one cubic meter of the material releases around nine liters of water into the room air.

Cross-laminated wood surfaces are warm


The cross-laminated wood surfaces can be used natural or color-treated.

Photo: Brüninghoff

The EN ISO 7730 standard defines the comfort temperature in a room as the average of the air and surface temperature. The temperature of wall surfaces made of cross-laminated timber is always close to the air temperature: in a room that is 21 degrees Celsius, you measure 20.1 degrees Celsius on the surface of a 24 centimeter thick component, while the outside temperature is minus 1.1 degrees Celsius. If you build or plank with “cold” materials, the surface temperatures will be lower: In order to reach the comfort temperature, you have to increase the air temperature - turning the heating costs energy and money.

Robust larch

Construction elements made of cross-laminated timber are available as fixed and finished external walls; the top layer on the room side consists of a wood of your choice in visible quality, on the outside of larch. Their wood is particularly resistant and is suitable as a facade without additional chemical wood protection - wood professionals sometimes refer to the larch as the oak among the conifers. Larch wood weighs 25 percent more than spruce, cross-laminated timber with top layers made of larch achieve higher sound insulation values. Particularly sensitive builders choose basement ceilings made of larch wood to shield various types of impulses such as earth radiation and water veins from geological interference zones, electrical and electromagnetic radiation.

Healthy Swiss pine

Scientists from the research company Joanneum Research in Graz compared the relaxation quality of a pine wood room and a wood decor room as a test. The subjects in the stone pine room showed a lower heart rate under physical and mental stress, in the subsequent resting phases the vegetative recovery process was faster. Stone pine is also considered to be insect-repellent and antibacterial - in a damp environment, a significantly higher bacteria-inhibiting effect of stone pine can be seen compared to other types of wood such as beech, maple and poplar.

Cross-laminated timber in decorative colors

Many planners and builders appreciate the constructive advantages of cross-laminated timber elements, but do not want a natural wood tone. Surfaces outside and inside can be adapted to regional architectural style or personal taste with planking, plaster or:

  • Top coat - covering coat hides wood tone and grain, you get a homogeneous, continuously colored surface;
  • Glaze - glazing of the elements reveals the grain of the wood, the natural wood color influences the brightness and tint of the color pigments;
  • Lye - Lye is mainly used to treat larch outdoors so that the wood surface turns gray and even in advance.

Reliable fire protection with cross-laminated timber

Cross-laminated timber houses do not burn more often than conventionally constructed buildings - but they are predictable and without harmful substances that are harmful to health and the environment. In a test with 1, 200 degrees Celsius heat on the inside of a ten centimeter thick building element, the temperature on the outside increased by only 9.5 degrees Celsius - an effect that also has the other advantages: if the summer sun glows on a roof element, for example, it stays in Room pleasantly cool. Fire eats through a component at 0.67 millimeters per minute, which provides information about the duration of a fire. The connections of the solid components are gas and smoke-tight and prevent burn-through - every room cell functions like a capsule in the event of a fire. In the event of a fire, for example, with a five-layer structure, two layers can burn away completely, leaving a three-layer cross-laminated timber with surfaces that are closed on both sides.

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