Straw insulation - the natural insulation solution for lightweight construction

Straw is a natural and ecological insulating material. It has good thermal insulation properties, is vapor-permeable and offers good sound and heat protection. Soil insulation has hitherto been used mainly in lightweight constructions based on wood.

Straw has been used as a construction and insulation material for millennia. Increased importance in the modern construction industry gained straw insulation from the 19th century, after it was possible to press straw bales by machine. On a larger scale, straw was first used as an insulating material in the USA and from there also to Europe. The market significance of straw insulation in this country has been relatively low so far, but due to the trend towards ecological construction and renovation, the natural material is becoming increasingly important.

Table 1: The characteristics of straw insulation at a glance

thermal conductivity0.051 - 0.055 W / mK
Building material classAlt: B2, New: E (normally flammable)
minimum insulation thickness according to EnEV 201441 cm
density120 - 150 kg / m3
Price per m210 - 15 EUR

How is straw used for thermal insulation?

Straw for thermal insulation comes from rye, wheat, barley or oats. For thermal insulation it is used in the form of pressed straw bales or straw building boards. In addition, straw can be used as a lightweight additive in other building materials - usually in clay products - use. Straw building boards play in practice in this country so far almost no role.

Price and manufacturer of straw insulation

The m2 price of pressed straw bales for thermal insulation is around 10 euros. Compared to other common insulating materials - such as mineral wool or polystyrene-based insulation (EPS, XPS), which play the biggest role in the German insulation market - straw is almost unrivaled in price. Pressed bales of straw for thermal insulation can be obtained directly from farms. As well as composite materials with straw, they are also offered by various manufacturers of natural building materials. Binding price lists of the various suppliers do not yet exist.

Which building physics properties does straw have as insulating material?

The thermal conductivity (lambda) of straw is between 0.051 and 0.055 W / mK (watts per meter x Kelvin). Its insulation performance is rather moderate compared to other insulating materials, which can be regulated by the thickness of the insulating layer. Straw insulation provides excellent sound and heat protection. The legally prescribed Rw sound insulation value of 50 dB is generally significantly exceeded by straw insulation.

Open to diffusion and capillary activity

With a water vapor diffusion resistance of 1 to 2? - Straw is a highly permeable and capillary active insulation material. Thus, straw insulation effects a very good moisture regulation of the building and contribute to a pleasant climate in the interior.

Fire protection

When loose, straw is considered flammable material and may be used as a building material only in the context of composite materials. Pressed straw bales reach the building material classes B2 / E (normally flammable) even without the addition of flame retardants. The fire resistance of the insulating material increases with the degree of compression.

Table 2: Comparison of straw and other thermal insulation materials

insulation materialsThermal conductivity (W / mK)Minimum insulation thickness according to EnEV (cm)Cost per m2 (Euro)
straw0,051 – 0,0554110 - 15 EUR
hemp0,04 – 0,0451610 - 27 EUR
reed0,040 – 0,0551810 - 20 EUR
rock wool0,035 – 0,0451410 - 20 EUR
EPS / Styrofoam0,035 – 0,045145 - 20 EUR

Application areas of straw for thermal insulation

Straw insulation is mainly used for thermal insulation of lightweight constructions. A typical field of application are insulation of buildings in wooden frame, wooden stand and wooden panel construction. For houses in timber frame construction, load-bearing straw insulation is also possible, but must be approved by the building inspectorate on a case-by-case basis. Straw insulation is suitable for:

  • Facade insulation: In this area, straw can be used both for external insulation and for interior insulation of exterior walls. The plaster is then applied directly to the insulating layer, alternatively, an outer lining with timber or wooden boards done.
  • Roof insulation: As an external insulation for the roof, straw is particularly suitable for pitched roofs with scaly roofing and good rear ventilation in order to optimally protect the insulation from moisture. On the straw insulation should be an outside over-insulation - for example, by Holzfaserdämmplatten - lie. In addition, straw can be used for intermediate sparing insulation.

Advantages of straw insulation:

  • Very good sound and heat protection
  • Economic efficiency: Due to the low basic price, straw insulation is an economical method of insulation, although the 2014 Energy Saving Ordinance (EnEV) stipulates a comparatively high minimum insulation thickness for straw insulation.
  • Open to diffusion and capillary activity
  • Uncomplicated processing
  • harmful substances
  • Easy disposal, compostability.

Disadvantages of straw insulation:

  • Individual building authority approval: If the straw insulation is to take place on a load-bearing wall, a case-by-case approval from the building authority is required.
  • Limited moisture resistance: straw insulation is only suitable for use in a largely dry environment. Straw is therefore not suitable as a core insulation for double-shell masonry. Straw-insulated facades should be additionally protected, especially on the weather side against the weather, which is achieved for example by a particularly large roof overhang.
  • Limited Pest Control: In order to prevent pest infestation, quick plastering of the building and the use of insect screens for the rear ventilation level are recommended.
  • Combustibility.

Tips & Tricks

Straw is a natural insulating material with ecological qualities, which is used in the form of pressed straw bales and in composite building materials - especially in combination with loam. Straw insulation is permeable and capillary active. They provide good insulation performance and provide efficient sound and heat protection. Straw insulation usually comes without chemical additives. Your vulnerability lies in limited moisture resistance.

Video Board: Straw Board &Grass products machinery and equipment