Rock wool - for cost-effective and efficient thermal insulation


Rock wool is a "classic of thermal insulation", which leads the list of insulation materials in Germany together with glass wool. The material impresses with its high insulation performance. The price / performance ratio of rock wool is very cheap.

Rock wool is an insulating material made of natural stone fibers, which has excellent insulating properties as well as heat and sound insulation properties. Together with the now obsolete slag wool and glass wool, rock wool belongs to the mineral wool. Due to their physical properties but also their favorable price, glass or rock wool insulation is one of the most commonly used insulation methods in Germany.

What are thermal insulation materials?

As insulation materials are referred to building materials, which have a large volume due to numerous cavities with low weight. Their thermal insulation effect results from the air resting in them, which have a low thermal conductivity compared to solids. The specific thermal conductivity (lambda) of insulating materials used today is significantly below 0.1 W / mK. Efficient insulating materials play an essential role in energy-conscious construction and thus contribute to the reduction of greenhouse gases. The insulation requirements for new buildings and renovations are also legally required by the Energy Saving Ordinance (EnEV).

The thermal conductivity of insulating materials in comparison

insulation materialsThermal conductivity (W / mK)Minimum thickness according to EnEV (cm)Cost per m2 (Euro)
rock wool0,035 – 0,0401410 – 20
glass wool0,032 – 0,0401410 – 20
Styrofoam / EPS0,035 – 0,045145 – 20
calcium silicate0,0652480
hemp0,04 – 0,0451610 – 27

Glass and rock wool - in the heat insulation materials on the top spot

In Germany, about 35 million m3 of insulation materials are used each year. Estimates assume that glass and rock wool have been represented here since the 1990s with a share of more than 60 percent. In addition, there are a variety of other insulating materials of synthetic raw materials, but increasingly also of organic material.

Rock wool - an invention from the 1930s

Rock wool was developed by the Bergisch-Gladbach company Grünzweig & Hartmann in the 1930s and patented in 1939 under the brand name "Silan". The goal of their inventors was to develop an insulating material whose starting materials were permanently available and to strengthen the competitive position of the company compared to the already longer established producers of glass wool - also a German invention from the 1930s.

How is rock wool produced?

Rock wool is produced from natural rocks at temperatures of about 1,500° C in the nozzle drawing process, the resulting rock wool fibers are then spun into a nonwoven. The usual starting materials are various diabase rocks, basalt, feldspar or dolomite. Today, recycled parts are also used pro rata for their production. In addition, there may be rock wool recyclates. The binder content is about 4%. In small amounts (less than 1%), mineral oils and silicone emulsions are also added to it which enhance their hydrophobic (water-repellent) properties.

Possible applications in many product variants

In the trade comes rock wool in the form of felts, braids, mats, plates, also a use as loose bulk insulation is possible. Including rock wool aluminum-laminated, DIN standard 4102-1 assigns it to building material classes A1 or A2; non-woven or paper-clad rock wool is classified as B2 building material. Criteria for the classification are the respective fire and flammability behavior.

What advantages does rock wool offer as an insulating material?

Rock wool has excellent insulation properties. Their thermal conductivity is 0.035 to 0.040 W / mK and is thus at a level comparable to the thermal conductivities of glass wool, hemp or polystyrene foam (EPS, Expanded polystyrene particle foam). In the current EnEV (as of 2014) an insulation thickness of at least 14 cm is specified for the thermal insulation with rock wool, but for roof insulation it should rather amount to 20 cm. Other benefits of rock wool include:

  • High sound insulation capabilities: Rock wool is therefore often used for sound insulation in floor slabs and Raumabschottung.
  • Very good heat protection properties: The relatively high bulk density of rock wool causes the heat energy of solar radiation to be released into the interior of the building with a time delay. The heat protection factor depends on the thickness of the integrated rock wool insulation layer.
  • No absorption of moisture: Rock wool is consistently water-repellent and unable to retain moisture. It is therefore an extremely "breathable" insulating material - moist air diffuses freely through the outer wall. With these properties, rock wool contributes to the protection of the building fabric from moisture and mildew and to a pleasant indoor climate in the building. The moisture and drying behavior of rock wool is generally rated as good by experts. Especially biogenic (organic) insulating materials rock wool is clearly superior in this regard.
  • Resistance to vermin and mold infestation.

What are the disadvantages of a rock wool insulation?

  • Stone wool, like glass wool, does not tolerate high levels of moisture and therefore can only be used in largely dry environments. When rockwool is moistened, its insulating effect is gradually lost. At very high moisture loads, the material collapses so that its insulating effect can no longer develop.
  • The relatively high bulk density of rockwool draws in comparison to various other insulation materials and a higher weight load of the building structures by itself. Especially with steep roof insulation therefore lighter insulation materials are often used.
  • The production of rockwool is comparatively energy-intensive, for each m3 between 150 and 400 kWh of primary energy are required for their production. However, the production processes of most other synthetically produced insulating materials are also energy intensive. The fact that rock wool does not occupy a top spot here is illustrated by the consumption values ​​of so-called gray energy - the total amount of energy required for production, transport, distribution, storage and disposal of products. Here rock wool lies at best in the good midfield and is also clearly superior to glass wool as its direct competitor product. In addition, effective thermal insulation permanently improves the energy balance of buildings.

What applications of rock wool in thermal insulation are there?

As a thermal insulation stone wool is mainly used for roof and ceiling insulation. One of their main uses is the intermediate spar insulation of roofs. One exception is steep, fragile roof constructions, whose insulation is more likely to use the lighter glass wool. The insulation is done here mainly in the form of insulation mats. For facade insulation with rock wool especially fleece laminated insulation boards are installed. In addition, rockwool is also used as a loose insulating material for blow-ins in cavities, roof slopes and non-accessible storey ceilings.

Excellent fire protection properties

Due to their good fire protection properties, rock wool is a good alternative to styrofoam both for roofs and façades. It begins to melt even at temperatures of just over 100° C and releases extremely flammable substances at temperatures of around 300° C. Rock wool is not flammable, the flash point of the rock wool fibers is over 1,000° C.

Cutting and removal costs

Sheets of flat, mat or nonwoven fabric must be cut before use, which is best done with a special insulation knife, but also with a serrated household knife or other alternative equipment. When loosely laid, the dismantling effort for rock wool is low, but the dismantling of a fortified rock wool insulation is complex.

Rock wool or glass wool - what's better?

Rock wool and glass wool have comparable properties. Stone wool, however, gradually has better heat and sound insulation properties. Due to their lower bulk density and consequently a lower weight, glass wool is sometimes better suited for insulating work on rather fragile constructions. The price of rock wool and glass wool is almost identical. Facade insulations with rock wool are relatively more economical to implement, a roof insulation is cheaper with glass wool - the decision between the two materials, however, should fall less on the basis of price considerations, but for structural reasons.

Comparison of costs for roof and facade insulation

insulationRoof insulation cost per m2 (EUR)Facade insulation Costs per m2 (EUR)
rock wool1010
glass wool720

How can you dispose of rock wool?

Rockwool waste arises when replacing old thermal insulation made of this material, when cutting and as a remnant of insulation work. Naturally, this insulating material is not biodegradable - proper disposal is therefore essential. In addition, rock wool is recyclable, from the "contaminated sites" new insulation materials are produced. It is best if users dispose of rock wool that is no longer needed by using a recycling service. For example, the manufacturer Rockwool has been offering this service on a nationwide basis since 2007; skilled tradesmen can order the recycling service together with a material order. Otherwise, this task is taken over by professional waste disposal companies. In Switzerland, manufacturer-specific recycling services for rock wool are now standard.

For recycling only unpolluted rock wool comes into question, dirty material ends up moistened and packaged in special bags on the building material landfill.

Is rock wool harmful to health?

There have been numerous debates in the past on the question of whether rock wool is harmful to health. Among other things, the material was said to have carcinogenic properties - but this assumption has not been confirmed by medical research. In 1999, the RAL quality seal for products made of mineral wool was introduced, which certifies their health safety, in Germany produced rock wool is now provided without exception. Within the European Community, comparable quality and health standards apply. However, renovations and demolition work may still be in contact with older and health-critical rockwool fibers.

In general, stone wool produced in Germany and Europe is not harmful to health. With proper, dense installation, a health burden from rock wool fibers is excluded, even indoors.

Fine dust by rock wool - good health and safety is important

During processing and especially when cutting rock wool, however, it may come into contact with fine dust. Anyone working with it should therefore protect themselves with gloves and a mask. Above all, professional craftsmen and construction workers, who regularly come in contact with rock wool and other mineral wool, should not do without a reliable breathing mask.

Tips & Tricks

Rock wool is suitable for economical thermal insulation of roofs and facades.
The material not only ensures excellent thermal insulation, but also optimizes the fire protection of a house. Rock wool produced in Germany and the EU is harmless to health - pay attention to the RAL seal of quality when buying.


Video Board: Rockwool Exterior Insulation vs Rigid Foam