The First-Ever Airtight Retrofit in the UK

Introduction

The Cambridge Institute for Sustainability Leadership (CISL) undertook a deep energy retrofit of a 1930s telephone exchange in Cambridge, targeting the EnerPhit Passivhaus standard. UCL Ltd was contracted to deliver a critical airtightness coating system across 2,000m² of interior surfaces — the first airtight retrofit of its kind in the UK.

Our Solution

Prior to application, interior walls were stripped back, exposing a variety of substrates including concrete and blockwork. All surfaces were thoroughly cleaned and dried before work commenced. UCL Ltd applied Blowerproof liquid airtight membrane by spray and brush to the soffits and walls, forming a flexible, permanent airtight barrier across the exposed substrates. Airtight tape was then installed at junctions and transitions to achieve a continuous, unbroken seal. The completed system met the stringent airtightness requirements of the EnerPhit standard, validating Blowerproof's performance across mixed substrate conditions in a retrofit environment.

Key Benefits

• First airtight retrofit of its kind completed in the UK
• EnerPhit (Passivhaus retrofit) standard successfully achieved
• Building now operates on approximately 15% of its previous energy consumption
• 2,000m² of mixed substrates treated, including concrete and blockwork
• Blowerproof applied by spray and brush, ensuring full coverage across complex surfaces
• Airtight tape integrated to provide a continuous, unbroken seal at junctions

Conclusion

UCL Ltd delivered a technically demanding airtight coating system that helped CISL achieve EnerPhit certification on a 1930s structure. This project demonstrates UCL's capability to execute complex airtightness solutions on retrofit schemes where no established precedent existed.