NBS Source
RockPrime® Blown Loft Insulation


Designed for use in between and over joists within loft spaces.


ROCKWOOL ROCKPRIME® is an energy and cost-efficient blown loft granulate that is mechanically installed, offering a speedy alternative to typical loft roll insulation with minimum disruption to occupants. It is made from sustainable volcanic rock and is impervious to air movement within the loft space.

Features and benefits:

  • Euroclass A1 non-combustible.
  • Quicker to install than rolls.
  • Suitable for new and existing lofts.
  • No wastage.
  • Does not rot or decay.
  • Assists in improving the acoustic performance of the ceiling.
  • Will not be displaced by air movement in the loft.
  • Does not offer sustenance to vermin.


The U-values shown in the table below are based on a loft space with joists that are 100 mm in depth:

  • 280 mm thick: 0.16 W/m²K.
  • 300 mm thick: 0.15 W/m²K.
  • 320 mm thick: 0.14 W/m²K.
  • 350 mm thick: 0.13 W/m²K.
  • 400 mm thick: 0.11 W/m²K.
  • 450 mm thick: 0.10 W/m²K.

General information


Mineral wool


Thicknesses available:

280 mm; 300 mm; 320 mm; 350 mm; 400 mm; 450 mm.


Uniclass 2015

Pr_25_31_48_48 Loose-fill mineral wool fibre insulationPrimary


P10/10 Loft insulation

P10/150 Blown loft insulation

Specification data - Loose-fill mineral wool fibre insulation Enhanced data


BS EN 14064.

Thermal conductivity (maximum)

0.047 W/m·K.

Fire performance

Euroclass A1 non-combustible.


Installing blown or loose laid loft insulation.


280 mm.

300 mm.

320 mm.

350 mm.

400 mm.

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Blown density (nominal)

23 kg/m³.

Third party certifications

  • KM 33106. : In accordance with BS 5803: Part 2 (Thermal insulation, pitched roof spaces in dwellings – pelleted or granular).