Text | Dieter Baltensperger, Stroba Naturbaustoffe AG
Previously used for ropes or clothing, hemp is now being rediscovered as a building material. This renewable raw material offers excellent insulating properties and binds more CO2 during its growth than other agricultural crops.
Hemp has been used for centuries, if not millennia. Hemp seeds are used as food and the fibers are valued for their high tensile strength. The ropes, clothing and ship's maps on Christopher Columbus' ships were made of hemp. After the plant fell into disrepute as an intoxicant in recent decades, its properties are now being rediscovered for a wide variety of applications.
14,5 t CO2 - more than any other agricultural crop in our latitudes. Around 90 m3 of insulation can be produced from the harvest. In comparison, 30 - 70 m3 of wood fiber insulation can be obtained from one hectare of an average forest.
mats, stones or concrete
The hemp stalks of the plant are obtained for the building material. The fibers are used to produce insulation materials, various molded parts or fleece. Half of the stalk consists of wood, which is used as hemp shiv to make hemp stone and hemp concrete. Insulation panels are made from hemp fibers with the addition of supporting fibers (binders for stability) in a thermo-bonding process, which are baked in large ovens and then cut to size. If the supporting fibers are made from plant-based raw materials, e.g. corn starch, the insulation is 100% biogenic. This soft hemp insulation is mainly used for roof, wall, ceiling or floor insulation and ensures a healthy, pleasant indoor climate. The area of application is the same as for conventional insulation materials. In order to achieve comparable U-values to mineral insulation materials, hemp insulation must be around 3 - 5% thicker. However, it can absorb up to 30% moisture without the lambda value falling. Other mineral or petrochemical insulation materials deteriorate significantly at a moisture content of 5%. To produce hemp bricks, the hemp shives are pressed with minerals and natural lime in the brick machine to form a brick and then air-dried. After a month of drying time, they can be used. Hemp bricks are mainly used in masonry constructions in combination with a wooden supporting structure and for infilling post and beam construction. During renovations, existing masonry can be clad with hemp bricks to improve the energy value. The thermal insulation value of hemp bricks is twice as high as that of bricks. Hemp bricks are often used in combination with soft hemp insulation.
Finally, with hemp concrete, the hemp shives and lime are mixed on site. The hemp concrete is placed in several layers in the slip formwork and compacted. After drying, the walls are plastered with lime or clay. Indoors, an unplastered or uncolored wall or ceiling can also become a special eye-catcher.
Good climate
Hemp is a high-quality natural insulation material with very good properties. It is considered to regulate moisture, offers good heat and sound insulation, is resistant to mold and is also recommended from a building biology perspective. Hemp building materials are CO2 sinks: The CO2 that the hemp absorbed during its growth is bound in the building material and is no longer released. Hemp has been used as thermal insulation in new and converted single-family and multi-family homes or office buildings since 1996. The most recent example is the district building in Feldbach/ZH. The ZHAW research project aims to show how a functioning circular economy can be implemented in buildings in the smallest of spaces. Natural building materials as well as durable, recycled and reused materials were used. The roof and walls are insulated with hemp panels with a thickness of 160 mm. Hemp is also popular for sound insulation. In the Bethlehemacker school building in Bern and the Röhrliberg school building in Cham, 30 mm thick hemp insulation was installed in the ceilings as a sound absorber.
Stroba Naturbaustoffe AG
8310 Kemptthal
www.stroba-naturbaustoffe.ch