Straw bale construction
A straw bale building is a structure that uses straw bales to build its walls . This type of construction mainly uses locally or regionally available resources ( wood , straw , clay , reeds, etc.). Compared to conventional construction methods, building straw bales is more labor-intensive, but more cost-saving.
history
Straw bale construction (or straw bale architecture) has existed since the end of the 19th century. In Nebraska , migrant workers used the balls like bricks to build walls. Later on in the USA the post construction with wooden posts developed. While the bales were originally used to build houses due to the lack of wood, nowadays the physical properties of the straw bales are in the foreground. According to the professional association for straw bale construction, there are around 80 straw bale houses and a few smaller commercial buildings in Germany, almost all of them in stand construction. In 2005 a three- story apartment building with 500 m² of living space was built in the Sieben Linden eco-village .
The load-bearing construction method has so far only established itself in Switzerland for reasons of building law. Since the turn of the millennium, some hybrid structures have been built in which the straw bales only take on part of the static functions. In Germany, this includes the Schmid-Hermanutz company in Langenau near Ulm. In Nax Mont-Noble in the Swiss Alps, construction of the first hotel from straw bales as a hybrid construction began in October 2011. The Maya Boutique Hotel opened in October 2012.
construction
A distinction is made between load-bearing and non-load-bearing construction. With the load-bearing straw bale construction, the walls consist entirely of straw bales and the roof load is carried by the straw bales. In the non-load-bearing construction, a wooden frame structure forms the supporting structure and the spaces ( compartments ) are filled with straw . This type of construction largely corresponds to the timber frame construction or the classic half-timbered house . In addition, numerous hybrid forms were tried out.
In hybrid structures, part of the load is carried by the straw, the other part by a supporting wooden structure (approx. 50/50). The straw bales have at least a stiffening function. This construction combines the advantages of both construction principles: Strong compression of the straw bales for high insulation values and controlled settling behavior . This construction principle was developed by architect Werner Schmidt in Switzerland since 2001 and is now very mature (in 2011: 20 existing buildings).
When constructing a bale of straw, particular attention must be paid to effective structural moisture protection, as bales of straw that have become damp lose their insulating effect and biodegradation ( rotting ) begins. A sufficient roof overhang and a moisture barrier against the ground, for example by means of a point foundation , must be ensured in any case.
The ideal plaster of a straw bale house consists of a base plaster made of lime with abrasion from clay , as this can absorb moisture quickly and later release it again.
The outer walls are either designed as a rear-ventilated facade , for example as a wooden or plaster facade . The rear ventilation creates a chimney effect that ensures permanent dehydration and counteracts overheating due to solar radiation in summer. In many countries, the straw must be directly covered with a material that corresponds to an EI30 fire resistance . In these countries there must be no space between the straw and the facade, i.e. no direct ventilation level above the straw.
Building material straw
Straw as a building material is very suitable for ecological house building . It protects the environment because as the grain grows, the greenhouse gas carbon dioxide is bound, the material can be procured without major transport costs and energy-intensive processing is not necessary.
Straw is a good natural insulation material . The measured thermal conductivity (Lambda10, tr) is 0.038–0.067 W / (m K), so the thermal insulation effect is similar to that of conventional insulation materials. Straw has an equilibrium moisture content of 8–18%. Properly built bales of straw show a high level of mold resistance. The gross density of the bales can be set between 80 and 210 kg / m³. The optimum density in terms of insulation is around 100–120 kg / m³. With increasing density, the thermal conductivity increases, so the thermal insulation effect decreases.
The production of straw bales for house construction is done with agricultural baling presses . The bales contain only straw and apart from the binding cords required for cohesion, no other additives.
Legal classification
Germany
In Germany, bales of straw produced according to defined criteria have a general building authority approval as a thermal insulation material and can therefore be used in non-load-bearing construction. The approval is limited in time and was renewed in the past by the Fachverband Strohballenbau Deutschland eV.
Austria
In Austria, straw bales meet the requirements for fire protection , as they - when strongly pressed - fall into the category of "normally flammable ". This corresponds to the minimum requirement in building law . With 5 cm clay plaster on both sides , modern straw bale buildings correspond to fire protection class F90 ( fire resistance period 90 min), which corresponds to a 20 cm thick concrete wall.
See also
literature
- Gernot Minke , Friedemann Mahlke: The straw bale construction . Ökobuch, Staufen near Freiburg im Breisgau 2004. ISBN 978-3-936896-01-5 .
- Gernot Minke , Benjamin Krick: Manual straw bale construction: Basics, constructions, examples . 2nd, completely revised and expanded edition, Ökobuch, Staufen near Freiburg im Breisgau 2009, ISBN 978-3-936896-45-9 .
- Heidi Snel: Straw in the head - an old building material rediscovered . DVD, 43 minutes, eco film, Hagelberg 2004. ISBN 3-938196-00-9 .
- Heidi Snel: Modern straw bale construction, straw in your head part 2 , DVD, 63 minutes, eco film, Hagelberg 2014, GTIN : 4260301390149.
- Herbert and Astrid Gruber, Helmuth Santler: New building with straw . 3rd edition, Ökobuch, Staufen near Freiburg im Breisgau 2008, ISBN 978-3-936896-35-0 ; 4th edition: New building with straw in Europe 2012, ISBN 978-3-936896-68-8 .
- Benjamin Krick: Investigation of straw bales and straw bale constructions with regard to their application for energy-saving construction with special consideration of the load-bearing construction . University of Kassel Press, Kassel 2008, ISBN 978-3-89958-422-6 (also dissertation at the University of Kassel 2008).
Web links
- Fachverband Strawballenbau Deutschland e. V. (FASBA)
- Austrian straw bale network
- Straw bale house in Leiferde. NABU-Kreisverband Gifhorn(detailed building description).
- Werner Schmidt: Straw bale house EFH - load-bearing straw bale construction. (Description of a load-bearing straw bale construction with a video of the construction process).
- Jürg Zulliger: Baupfusch: Only beetles and mice live healthy in the straw. In: Der Schweizerischer Beobachter , No. 23/2001, November 9, 2001
- Straw bale houses. gibbeco Genossenschaft Information Baubiologie, Switzerland: "For over 100 years, especially in North America, people have been building with straw bales"
Individual evidence
- ↑ Passive house technology and innovative constructions - straw bale construction. Archived from the original on January 16, 2009 .
- ↑ Bales of straw are good building materials. N24 , April 21, 2008, archived from the original on July 10, 2015 .
- ↑ Luzius Theler: A dream made of stone, wood, clay - and straw. NZZ , December 6, 2013 .
- ↑ Infill technology. Wooden stand or wooden frame. Archived from the original on January 24, 2016 .
- ^ Atelier Werner Schmidt. Architecture office. (Swiss page with lots of information and photos on load-bearing construction methods and realized buildings).
- ↑ European Technical Assessment, English, "Baustroh". DIBt Deutsches Institut für Bautechnik, June 21, 2017, accessed on May 7, 2020 . (PDF; 137 kB) German Institute for Structural Engineering
- ↑ Test report on the fire behavior of a straw bale wall. City of Vienna, October 6, 2000 .