Retrofit Airtight Project with Intelligent Membrane

Case Study: Oxford Retrofit Airtightness Upgrade

Overview with Intelligent Membranes

This retrofit project in Oxford saw Passive Purple Internal applied to the warm side of the insulation — on the outside of the property — before fitting new external wall insulation and a modern render system. This airtightness-first approach ensured the building was prepared for decades of energy-efficient performance.

Background

The property’s substrate was sound, making it ideal for liquid-applied membrane installation. A layer of Render Prime was applied to improve adhesion before Passive Purple application. The project was completed in just two days, with particular attention paid to airtight detailing. In retrofit projects, this detailing is vital — older buildings can have more gaps and irregularities, which we sealed using Passive Purple Brush.

Solutions

Applying Passive Purple before installing external wall insulation provided:

• Airtight and smoke-tight barrier across all external walls
• Enhanced energy efficiency by preventing heat loss
• Improved indoor air quality by stopping uncontrolled air movement
• Fire safety compliance through a robust membrane layer

This method ensures a long-lasting building envelope that performs in all seasons.

Results

The project achieved 0.4 ACH@50Pa — exceeding many new-build airtightness targets. This demonstrates the power of modern retrofit techniques to upgrade existing buildings into high-performance, low-carbon, energy-efficient homes.

Client Testimonial

"It was a big step but once work had started I knew it was the right decision. Passive Purple is a brilliant form of technology. Why doesn’t everyone know about this?"