Overview

Passive Purple External, combined with our full range of airtightness solutions—including Passive Purple Internal, Passive Purple Brush, and Airtight Fleece Membrane—delivers exceptional performance in timber frame construction. These products work together to create a robust, continuous airtight barrier that not only improves energy efficiency but also provides advanced moisture control for long-term building durability.

By sealing every junction, gap, and penetration, this system ensures a draught-free, comfortable indoor environment while dramatically reducing heating and cooling demands. In addition, the airtight envelope minimises the risk of condensation and mould growth, helping maintain a healthy living space. For timber frame projects aiming to meet or exceed modern building standards, Passive Purple offers a proven, high-performance airtightness and vapour control solution.

Background

The installation of Passive Purple External and Passive Purple Internal Facade Waterproofing Membranes on this timber frame project was completed with exceptional efficiency—taking just one week from start to finish. The absence of complications allowed for a smooth, uninterrupted workflow, showcasing the practicality and speed of our liquid-applied airtightness solutions.

This hassle-free process not only saved valuable project time but also ensured that airtightness and weatherproofing were achieved to the highest standard from the outset. By using a combination of Passive Purple External for robust outdoor protection and Passive Purple Internal for airtightness and vapour control on the warm side of the building envelope, we created a comprehensive barrier against air leakage and moisture ingress.

The result was a rapid, reliable installation that immediately enhanced the building’s energy efficiency and set a strong foundation for long-term performance.

Solutions

Achieving exceptional airtightness in timber frame construction requires a precise, methodical approach—and that’s exactly what we delivered on this project.

Sealing Joints and Openings
All door and window reveals were meticulously sealed with Passive Purple Brush, a fibre-reinforced liquid membrane designed for pinpoint airtightness in tricky detailing areas. Before this, an Airtight Fleece membrane was installed around frames and junctions to create a secondary layer of defence against air leakage.

This two-step process—first reinforcing with fleece, then finishing with Passive Purple Brush—ensured complete coverage of potential weak points. By eliminating thermal bridges and uncontrolled air paths, we dramatically improved the building’s airtightness, thermal performance, and long-term energy efficiency.

These measures not only contribute to lower heating and cooling costs but also align with Passivhaus-level performance goals, ensuring the home remains comfortable, draught-free, and moisture-protected for years to come.

Results

The airtightness strategy for this timber frame project delivered outstanding results, achieving an air change rate of 0.17 ACH (air changes per hour)—a figure far exceeding UK Building Regulation requirements and edging close to Passivhaus certification levels.

This exceptionally low rate is a clear indicator of a highly efficient building envelope, where uncontrolled air leakage has been virtually eliminated. As a result, the property benefits from:

• Reduced Energy Costs – Less air loss means lower heating and cooling demands year-round.

• Enhanced Indoor Comfort – Draughts are eliminated, creating a consistently warm and stable indoor environment.

• Improved Indoor Air Quality – The controlled building envelope prevents the infiltration of pollutants, allergens, and moisture-laden air.

• Long-Term Building Health – By minimising moisture ingress, the risk of condensation, mould, and structural damage is significantly reduced.

These results demonstrate how Passive Purple External, Passive Purple Internal, Passive Purple Brush, and Airtight Fleece membrane work in harmony to deliver airtightness, moisture control, and long-lasting performance in modern timber frame construction.

Air Testing – Ensuring High-Performance Airtightness

Air testing—also known as air permeability testing, air leakage testing, or air pressure testing—is a crucial step in verifying a building’s energy efficiency. This process measures the volume of air escaping through the building envelope, identifying any weak points where unwanted air leakage may occur.

A successful air test confirms that the structure meets or exceeds airtightness targets, ensuring the building is energy-efficient, comfortable, and moisture-protected. In high-performance builds and Passivhaus projects, achieving a low ACH (air changes per hour) score is essential for minimising heat loss, reducing energy bills, and maintaining consistent indoor temperatures.

By integrating Passive Purple airtight membranes into our projects, we consistently achieve exceptional results in air testing—proving the effectiveness of our approach and the reliability of our products.

Client Feedback – Passive Purple Delivers on Performance and Speed

“I couldn’t be happier with how my eco self-build has turned out. The attention to detail and the airtightness achieved are incredible. I’m particularly impressed with how quick the installation of Passive Purple was—it saved us valuable time without compromising on quality!”

This homeowner’s experience reflects the growing recognition of Passive Purple as a leading airtightness solution for eco self-build projects. By combining speed of application with exceptional performance, Passive Purple helps clients meet ambitious energy efficiency goals while keeping projects on schedule.