Straw-bale construction

A straw bale construction is a building, straw bales are used for the wall construction. In this construction, mainly locally or regionally available resources are used ( wood, straw, clay, reed, etc. ) can occur. Compared with traditional methods of construction of straw bale construction is labor intensive, but cost-saving.

History

The straw bale construction (or straw bale architecture ) has been around since the late 19th century. In Nebraska, the bales of migrant workers like bricks were used for wall construction. Later, the post and beam construction developed in the USA with timber framework. While originally the bales were used for lack of wood for building houses, are the physical properties of straw bales in the foreground today. According to the trade association straw bale building in Germany there are around 80 bales of straw - houses and some small commercial buildings, almost exclusively in post and beam construction. The load -bearing structure has been established from building regulations only in Switzerland. So-called " hybrid structures " have prevailed in recent years and have also been built in Germany (Haus " Schmid- Hermanutz " Langenau at Ulm). In Nax Mont- Noble, in the Swiss Alps, was started in October 2011 with the construction of the first hotel made ​​entirely of straw bales. The Maya Guesthouse was opened in October 2012. It is remarkable as the shower water is heated by excess heat is stored. For the buildings, is a hybrid structure.

Construction

A distinction is made between bearing and non-load bearing construction. When bearing straw bale construction, the walls are made entirely of straw bales and the roof load is carried on the straw bales. In the non-load bearing construction, a timber framework forms the supporting structure and the spaces ( partitions ) to be filled with straw. This type of construction is largely the timber frame or the traditional half-timbered house. In addition, numerous mixed forms were tried. Straw houses in concrete frame construction, which should be cheaper and more flexible than the timber frame construction, are listed in Switzerland in planning There are also so-called " hybrid structures ": Part of the load is transferred via the straw, the other part of a supportive wooden structure (about 50 / 50). This design combines the advantages of both design principles: Strong compression of straw bales for high insulation and controlled setting behavior. This design principle developed by architect Werner Schmidt since 2001 in Switzerland and is now very mature ( in 2011: 20 existing buildings ).

In the construction of a straw bale building must pay particular attention to effective structural protection against moisture, become as damp straw bale lose their insulating properties and biological degradation ( rotting ) begins. At a sufficient roof overhang as well as a moisture barrier to the ground, for example by a point foundation, it must be in any case.

The ideal plaster a straw bale house consists of a base coat of lime with an abrasion from clay, as it can absorb moisture penetrating quickly and release it again later.

The exterior walls are performed either as a ventilated façade, such as wood or plaster facade. The ventilation causes a chimney effect, which ensures a durable dehydration and counteracts direct sunlight in summer overheating. The straw must be in many countries directly covered with a material which corresponds to a fire resistance EI30. In these countries there is no gap between straw and façade may be, that is, no direct ventilation space above the straw.

Building materials, straw

Straw as a building material is very suitable for the ecological construction. It helps the environment, because the growth of the crop, the greenhouse gas carbon dioxide is bound, the material can be procured without great effort and transport energy- intensive processing is omitted.

Straw is a good natural insulation. The measured thermal conductivity ( Lambda10, tr) is from 0.038 to 0.067 W / mK, so that the heat insulating effect similar to that of conventional insulating materials. Straw has an equilibrium moisture content of 8-18%. Expertly built of straw bales have a great mold resistance. The density of the bales can be 80-210 kg / m³ set. The optimum density with respect to insulation effect is about 100-120 kg / m³. With increasing density, the thermal conductivity increases, ie the thermal insulation effect decreases.

The manufacture of straw bales for building houses is done with agricultural balers. The bales contain only straw and required for the cohesion of tie cords, no other additives.

Legal classification

In Germany have defined criteria Baustrohballen produced a general building approval as a heat insulating material and can therefore be processed in non -supporting construction.

Fire protection

Straw bales meet the requirements for fire protection, because - in the highly compressed state - " normal flammability " fall into the category. This corresponds to the minimum requirement in construction law. Both sides with 5 cm clay plaster meet modern straw bale building fire protection class F90 (fire resistance duration 90 min ), which corresponds to a 20 cm thick concrete wall.