The basic wall thickness is 97 mm, to which 16 to 20 cm of insulation is added. The U value at 16 cm of insulation amounts to 0.20 W/m2K (composition of exterior wall with ventilated prefabricated façade made of, for example, timber, is stated below). It is also possible to use the contact façade, depending on the type of thermal insulation and the chosen façade system. Since the solid CLT panels simply replace the traditional construction of brick or concrete, any type of finishing can be chosen with this system, but is must not contain any cement adhesive – not only from the ecological aspect, but also because cement does not bond to the timber base.
The Purbond adhesive is one of the eco-friendliest adhesives and is also used in other products such as kitchen counters, or in medicine. It was developed by Bayer. The timber logs cut into thinner lamellas can dry thoroughly in a short period of time, which stabilizes the timber structure, provides it with greater solidity and, above all, durability. Lamellas are then glued back to form laminated beams used in all types of timber structures. These adhesives are mostly based on other solvents and may contain formaldehyde, which accounts for their low price and the fact that they are applied only on small surfaces. With regard to cross-laminated panels, the development collaboration with Bayer and the decision to use Purbond has resulted in a product that is completely harmless to health as the second component in the bonding process is moisture contained in the timber. It can safely be said that Xlam structures are much more welcoming and environmentally friendly than other prefabricated timber structure systems where the timber frames are mostly closed by means of OSB panels which have an epoxy-based matrix. What is more, chipboards that are part of apartment furniture contain a lot more harmful adhesives, solvents and matrixes than Xlam structures.
The article describing the adhesive summarizes this as follows:
"Xlam components are glued into a cross-laminated structure by means of the one-component polyurethane adhesive Purbond which utilizes the natural moisture in timber to bond components. Since the adhesive contains no formaldehyde or solvents, it is completely harmless to human health. Due to its high bonding ability, this odourless adhesive enables spare consumption. In its solid form, it is completely inert and toxicologically safe as proven by decades of experience in its application on residential, medical and other surfaces (upholstered furniture, beds, sports textile, and medical implants). Since none of the adhesives used contain formaldehyde, Xlam structures are entirely comparable with natural solid timber."
An Xlam wall weighs around 40kg/m2, i.e. exactly the same as a timber frame structure with a 15 mm OSB panel which has twice as higher dry bulk density in comparison with timber. This means that, weight-wise, the OSB panel is equivalent to the 3 cm thick Xlam wall, while the weight of the timber frame, usually 16 to 18 cm thick in prefabricated construction, is equivalent to the remaining part of the 6.4 cm thick Xlam panel. In calculating structures, we thus take the same weight of walls into account in both cases. In such cases, however, Xlam structures have a significant advantage before all other traditional masonry and prefabricated systems. The connected system of panels and walls represents a system connected to form a stiff box which is a much more levelled load on the entire foundation plate. From the aspect of building on grounds with poorer load-bearing capacity, it is our expert estimate that this is currently the most recommendable system of construction. The foundation structure is executed as a RC panel with external rib element (due to frost), into which piles can partially be driven if necessary and if suggested by the calculation of tension in swampy foundation ground with poor load-bearing capacity.