What is stone wool?
Stone wool, also called rock wool or rockwool, is an insulation material made of fibres spun from molten rock, mainly basalt or diabase. The rock is melted in a furnace (manufacturer Rockwool quotes temperatures of up to about 1,500 °C), thrown off fast-spinning wheels into fine fibres and bound with a resin into batts, rolls and rigid slabs. Together with glass wool it forms the family of mineral wool.
Properties
- Fire: most stone wool products are classed A1 or A2-s1,d0 (non-combustible) under EN 13501-1, and the fibres withstand temperatures above 1,000 °C. That makes it a common choice for fire stops, cavity barriers and external wall insulation on taller buildings.
- Thermal: thermal conductivity (lambda) is roughly 0.032 to 0.040 W/m·K depending on the product. A lower value means a thinner layer for the same thermal resistance.
- Moisture: water-repellent and vapour-open, but wet stone wool insulates poorly and wet rolls can sag.
- Sound: the open fibre structure absorbs sound well, which is why it is used in partitions and between floor joists.
Application
- Pick the product for the job. Rolls suit lofts and joist floors; rigid slabs suit walls, flat roofs and render systems. Cavity batts, facade slabs and high-density roof boards are different products.
- Use slabs or batts in vertical work. Loose rolls in a wall or cavity can slump and leave cold gaps at the top.
- Follow local cavity practice. In the UK full-fill cavity batts are common, within the manufacturer’s limits for driving-rain exposure; in the Netherlands a ventilated air gap is normally kept in front of the insulation.
- Put the vapour control layer on the warm side and use a vapour-open membrane on the cold side.
- Protect skin and lungs when cutting: gloves, long sleeves and a dust mask.
Common mistake: using a soft batt where it will carry load, such as under a flat roof membrane or a floating floor. Use a high-density board designed for compression.
Related terms
- Mineral wool
- Glass wool
- Cavity wall insulation
- Insulation value (Rd value)
- Fire classification
- Basalt
- Sandwich panel
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