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



Starting point / motivation

Untreated wheat straw in form of straw bales as well as in form of chopped blow-in insulation material is a technically approved thermal insulation material in the EU and achieves the Euro classification "E" (normally flammable) according to EN13501-1.

Compared to competing building materials such as cellulose and wood fibre, straw insulation has considerable advantages in terms of its ecological balance, in particular the "embodied energy" and the CO2 equivalents. In addition, the base material does not compete for land with the nutrition industry; rather it is an annually renewable residue from agriculture. Calculations have shown that the volume of wheat straw harvested annually in Austria enables a substitution of synthetic and mineral insulation materials of 95%.

Blow-in insulation is the purest form of thermal insulation, as it does not feature contamination from adhesives, binders or dowels, which makes it easily reusable. In addition, blow-in straw insulation is the most practicable material form for logistically optimized large construction sites and for factory prefabrication, since its installation requires only little physical effort.

Contents and goals

The vision of the research project URBAN STRAW is to make the advantages of straw insulation known from single-family house constructions applicable to multi-storey urban buildings. The focus is hereby on improving fire protection, since for the exterior insulation material of walls and roofs in building classes 4 and 5 require the euro-classification "B" (hardly flammable) according to the guideline OIB RL 2 in Austria.


On different levels of laboratory scale, chopped straw, as commonly used for blow-in insulation, is chemically conditioned against fire using biogenic flame-retardants of material-related building materials without negative ecological and human-toxic properties and introduced into the straw chops in various technical application processes. By means of fire tests of different degrees of specialization, the optimal material composite to achieve the classification "B" according to EN13501-1 is to be determined in the selection process. The fungicide properties of the new material will also be investigated.

Prototypes are then created with test elements based on prefab timber construction and system-complementary products using the resulting insulation material composite. The timber elements will also meet the requirements of OIB RL 2 for the use of multi-storey buildings class 5 with up to 6 storeys in terms of fire protection and structural engineering. The advantages of wooden hybrid rib elements are to be tested due to their construction-related chamber design for blow-in straw insulation.

Expected results

It is expected that the combination of the conditioned straw insulation and the material-efficient timber rib elements will result in a very CO2-efficient structural system, which enables a climate-friendly net-zero architecture for cities of the future.

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