Passive Purple and Rockwool® officially verified as the perfect low energy building combo

Recently, through the Building Physics, Construction and Services research unit at Ghent University’s Faculty of Engineering and Architecture, Passive Purple and Passive Purple External were put to the test. Passive Purple was applied on concrete block walls with Rockwool® RockSATE Duo Plus insulation panels to assess the impact of different installation support anchors.

Rockwool® RockSATE Duo Plus is a rigid panel of uncoated, double-density volcanic rock wool. It’s designed specifically for facades with external thermal insulation systems. Its high-density outer layer allows for optimal adherence of the render, and the lower density inner layer enhances the thermal performance of the panel.

On paper, Rockwool® RockSATE Duo Plus and the Passive Purple range looked like a match made in eco-building heaven. But we wanted that paper validated. So we took it to Ghent University to be put under the microscope.

Ghent University assessment

Greater airtightness with Passive Purple & Rockwool

Ghent University measured the impact of the installation of different insulation support anchors on the airtightness of a single wythe concrete block wall with a liquid-applied airtightness coating. To control the environment and guarantee real-world verification, these tests are performed in a full-scale test setup built in a steel box, according to EN 12114:2000 “Thermal performance of buildings – Air permeability of building components and building elements – Laboratory test method”. Two 9cm concrete block walls were treated with Intelligent Membranes Ltd coatings (Passive Purple), and the airtightness was tested according to EN 12114:2000.

  • Intelligent Membranes Ltd PASSIVE PURPLE: 0.019 m³/h.m² @ 50Pa
  • Intelligent Membranes Ltd PASSIVE PURPLE EXTERNAL: 0.067 m³/h.m² @ 50Pa

Two single wythe walls of 9cm thickness were constructed in steel frames using solid concrete blocks. The walls are 1070mm wide and 2390mm high, which yields a surface area of 2.557m². One wall was then treated with Passive Purple, and the other was treated with Passive Purple External. Both products were applied with an airless spray machine, and the application thickness was around 700g/m² (within specifications of the manufacturer; 500 – 800g/m²).

The effect of different insulation anchors was measured on both coatings, installed on an 80mm Rockwool® RockSATE Duo Plus, with and without the Rockwool® REDArtTM Capa Base Casa mortar. 


The findings were as follows:

  • Additional air loss due to the anchors ranges between 0.000 and 0.003 m³/h per anchor at 50Pa.
  • Differences between anchor types can rather be attributed to inherent variability than systematic differences
  • Absolute impact at 50Pa for 5 anchors is limited to 0.015m³/h.m²
  • Mortar of the insulation panel reduces the air leakage rate through the reference wall and reduces the impact of the anchors.

In a nutshell, the Passivhaus certified range, Passive Purple, delivers even greater airtightness when used in combination with Rockwool‘s RockSATE Duo Plus insulation panels. Together these two building products are enabling the construction of eco-friendly buildings with year-round comfortable indoor temperatures, thanks to nature and a little help from these innovative building materials.

Rockwool & Passive Purple for great airtightness

Check out the Passive Purple range and contact Adam and the team at Intelligent Membranes to discuss your next environmentally conscious, low energy build

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