Rebuilding for Performance: A High-Efficiency London Retrofit

Retrofitting existing buildings presents unique challenges, particularly when aiming to achieve modern standards of airtightness and energy efficiency.

This London retrofit project involved a complete internal strip-out, extensive refurbishment works and new extensions, transforming an existing property into a high-performance, future-ready home. By combining careful preparation with Intelligent Membranes' Passive Purple airtightness system, the project achieved an impressive airtightness result of 0.3 ACH, helping to reduce energy demand while improving comfort and long-term building performance.

The Challenge

Turning an Existing Building into a High-Performance Home

Unlike new-build projects, retrofit schemes must work around existing structures, hidden defects and complex junctions.

Following the full strip-out, the project team identified and sealed potential air leakage pathways throughout the building. Junctions, penetrations, service routes and difficult detailing areas required particular attention to ensure a continuous airtight layer could be achieved across the entire building envelope.

The Airtightness Solution

To create a robust airtight envelope, a combination of Intelligent Membranes products was specified:

• Passive Purple Brush for junctions, penetrations and connection details
• Airtight Fleece Tape for critical transitions and reinforcement
• Passive Purple Internal Vapour Control Membrane applied across walls and ceilings

This liquid-applied system enabled complete coverage of complex geometries while eliminating the gaps and overlaps often associated with traditional sheet membranes.

Installation Process

The installation followed a structured sequence designed to maximise airtightness performance:

• Full internal strip-out
• Detailed sealing of junctions and penetrations
• Installation of Airtight Fleece Tape
• Spray application of Passive Purple Internal Vapour Control Membrane
• Coordination with follow-on trades to protect the airtight layer

This approach ensured continuity throughout the building envelope and reduced the risk of performance gaps.

Results That Speak for Themselves

Airtightness Achievement

The completed project achieved an impressive airtightness result of:

0.3 ACH

This exceptional level of performance helps deliver:

• Reduced energy consumption
• Improved thermal efficiency
• Greater occupant comfort
• Enhanced durability of the building fabric
• Reduced uncontrolled air leakage

The result demonstrates how careful preparation, robust detailing and the correct airtightness strategy can dramatically improve the performance of existing buildings.

Thinking of a retrofit? Contact us today.