The hygroscopic insulation material
Since we are not living in the fifties, a handsome half-timbered structure can be shown. External insulation - possibly also clad - is therefore ruled out from the outset.
Interior insulation is available from a wide variety of raw materials and in a large range of qualities and construction methods. Either in old half-timbered houses or in modern timber frame constructions, the interior insulation must meet an important criterion in order to harmonize with the construction: it must be able to remove moisture from the room air, from driving rain and any leaks between the framework and infill and remove it so that it does not cause damage. The insulation materials used, like the entire wall structure, must be hygroscopic (i.e., thanks to their diffusion-open properties, they must be able to absorb moisture and pass it on by capillary action). All organic ecological insulation materials meet this criterion, but foam glass panels and foam glass gravel are mineral, they do not absorb water and are capillary-tight.
Clay in the house
Clay plays an important role in half-timbered houses, and so does the insulation. Loam has a number of properties that are extremely advantageous in terms of construction technology and building biology.
It is known that clay plaster regulates the humidity of the room air through absorption, storage and release. What is less well known is that earth building materials can also do this with wood: the earth is permanently able to remove moisture from the wood and thus protects it from decay over the long term. The beam should therefore - except on the visible facade side - be firmly covered with clay at every possible point. The contact between clay and wood is therefore by no means harmful for a half-timbered house, but rather necessary for its long service life.
If a panel material is to be used as interior insulation, the surface of the substrate must be prepared. This leveling should be done with a clay, for example with a light or heavy clay plaster.
Clay has been used in half-timbered construction for a long time; with an added lightweight aggregate, it is ideally suited as an insulation layer plastered on the inside. In such an application, it is also advisable to apply a homogeneous layer to the framework. This ensures that all joints are tight, especially against drafts, and that here too the wood is sufficiently encased in clay to protect it from decay.
Light-clay mixed by yourself
Light clay is offered as a ready-made mixture, but you are free to to mix it yourself. This makes it possible, for example, to reproduce historical building materials. However, when mixing your own light clay, you should ensure that there is a sufficiently high proportion of clay so that the dehumidifying effect remains. If the proportion of lightweight aggregate is too high, the clay cannot effectively dehumidify the wood.
Solid wood as a carrier
As with all insulation, when using stuffing materials (e.g. hemp), loose fill or blown cellulose, a wall structure that is open to diffusion is necessary in order to benefit from the climate-regulating properties of ecological building materials. Therefore, OSB panels and foils have no place as a finishing touch in the framework. Instead, solid wood is the material that can be used for the outermost layer of a completely diffusion-open wall structure. Finally, a plaster base made of reed and clay plaster or clay building boards can be attached to the wood.