Straw as building material
Using straw as insulation is a relatively recent practice. By means of tests and analyses plenty of its features and characteristics are known and defined by now. Neither vermin nor moisture and fire can harm professionally installed bales of straw. However, certain rules must be followed so that the approved quality characteristics are valid on a German construction site. The straw bales from nearby fields have to turn into an approved construction material proven to be applicable for its purpose.
Such a proof of applicability can be the general building supervision (Allgemeine Bauaufsichtliche Zulassung) Z-
Depending on the intended type of construction it can be necessary to not only make use of approved bales of straw for building, but additionally to request an individual approval from the supreme construction supervision of the respective state.
How well do straw bales insulate?
Straw bale insulated construction components outperform the thermal insulation requirements. The approved thermal insulation material "bales of straw for building" is characterized by a proven and regularly officially controlled thermal conductivity. The rated value for calculating the U-
How high is the fire risk of straw bale insulated construction components?
Bales of straw as construction material feature excellent fire protection. Thorough production of the bales of straw for building as well as the inspection of an approved supervisory board ensure high grade straw bales. Thereby these straw bales can be classified into the building material class ‘normally flammable’ (DIN 4102 -
Yet another cladding of the straw not only completes the construction component, but enhances the fire protection. For this purpose, it is advisable to apply a mineral facing of at least 10 – 20 mm. On the inner surface this might be clay plastering directly applied to the straw. Flammability tests could demonstrate that already a 8 – 10 mm thick clay plastering can result in a fire-
Moisture in straw bales on exterior components will not raise a problem if a construction pervious to vapor plus an adequate exterior cladding are being used. They also need to be effectively protected against driving rain. The indoors plastering has to be free of cracks and as airtight as possible. While installing the bales of straw and applying the plastering the seasonal climate has to be considered. In general, the facing has to be finished before winter. The current general building supervision specifies a detailed framework which complicates the direct plastering. Further studies and verification shall be done until 2014 to achieve a general proof of usability for the direct plastering of exterior walls insulated with straw. At present individual case surveys already exist demonstrating that under certain circumstances a straw bale wall plastered directly with lime is complying to the general building supervision.