URBAN STRAW - Fire protection conditioning of blow-in straw insulation material and its structural application for urban building classes 4 and 5

Investigation and development of fire protection conditioning of chopped straw blow-in insulation based on biogenic flame-retardants of similar building materials and their application methods. Use of the material as external thermal insulation in material-reduced prefab timber construction elements for urban building classes 4 and 5 up to 6 storeys.

Short Description


completed (Dezember 2022)

Starting point, content and results

Straw is one of the oldest building materials and has been used in a variety of ways throughout history: be it since early times as roofing material and to reinforce earth building elements, as straw panels for facades or since the end of the 19th century in straw bale construction, which is regaining popularity since the end of the 20th century in the course of the greening of the construction sector. The special ecological advantages of the material lie in the fact that it requires little manufacturing energy, is easy to dispose of through composting and has a good CO2 balance, since the grain plants absorb more carbon from the atmosphere during growth than the processing of the straw into insulating material cause emissions. According to a current article in the online edition of the magazine GEO, this low-energy construction method is currently experiencing a renaissance in Germany. Building insulation made from regrowing renewable raw materials still have a low market share of around 4-5% in Europe, but the trend is rising. According to a study by the TH Braunschweig and the Fraunhofer Institute "More than just insulation - additional benefits of insulating materials made from renewable raw materials", one reason for this lies in the building authority requirements that restrict the use of combustible building materials. Flame-retardant building materials have a much wider range of applications, for example as thermal insulation systems for facades in the higher building classes 4 and 5, which are prevalent in urban areas. However, the goals resulting from the Paris climate agreement for the decarbonization of the construction sector require the increased use of regrowing raw building and insulating materials, also in multi-storey buildings in urban areas - both in new construction and in the case of additions and renovation.

The motivation and vision of the "Urban Straw" project is to establish straw insulation as a common, commercially available insulating material for multi-storey urban construction projects and to herby significantly increase the applicability of the material by using it in larger construction projects. Especially in multi-storey timber constructions, which are said to have a high future viability due to its ecological qualities, straw is an optimal insulating material and an ideal material supplement. Both fire protection treatments with ecologically and human-toxically harmless chemical additives of material-related building materials as well as simple constructive fire protection solutions with ecologically high-quality materials are examined for their applicability with blow-in straw insulation. The ecological advantages of the straw should hereby not be impaired and the insulating material should in any case remain compostable at the end of its life cycle. In order to chemically treat the straw substrate the methods of mix-conditioning with different mixers and pressure impregnation in a laboratory autoclave are applied. Since blow-in insulating material requires a compartment cover on the facade anyway, structural solutions with a constructive shielding of the untreated straw by a new type of facade membrane with a very high level of fire protection and by traditional wood wool boards are being investigated in comparison. The selection of the best possible, practical material combination is achieved through several fire test series of different approaches with flaming and heat radiation.

The result shows that the constructive shielding of the straw against the fire with wood wool panels, which were originally developed by Robert Scherer in Vienna in 1908, is superior to the chemical treatment. It turns out that the fire rating and the material thickness of the panels are only insignificant factors. Above all the straw remains completely untreated with this application and no adaptation of the production plant is necessary. This constructive solution also appears to be easily transferrable to other regrowing blow-in insulation materials, such as flakes made from recycled cotton or flax.

Project Images

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Project Partners

Project management

Architect DI. Peter Schubert RIBA, capital [ A ] architects ZT-GmbH

Project or cooperation partners

  • Sebastian Stenzel, BSc. - DPM Holzdesign GmbH
  • Prof. DI. Dr. Azra Korjenic - TU Wien, Forschungsbereich Ökologische Bautechnologien (E207)

Contact Address

capital [ A ] architects ZT-GmbH
Architekt DI. Peter Schubert RIBA
Billrothstraße 86/1
A-1190 Vienna
Tel.: +43 (1) 925 77 88
E-Mail: office@capital-a.at
Web: www.capital-a.at