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The First-Ever Airtight Retrofit in the UK

Applying a Blowerproof airtight membrane to a 1930’s telephone exchange


The Cambridge Institute for Sustainability Leadership (CISL) wad undergoing a pioneering retrofitting project for its new headquarters. Their vision was to create an ultra-low carbon, sustainability hub that set new energy-use standards.

To achieve this, they transformed a 1930’s telephone exchange in Cambridge with a deep energy retrofit to the Passivhaus standard, EnerPhit. It now operates on just 15% of its previous energy.


To achieve the EnerPhit standard an improved airtightness system was required. As part of the system, Ultimate Coatings Ltd. was contracted to apply Blowerproof to the interior surfaces of the building to create a flexible, permanent airtight coating.

Prior to application, the interior walls were stripped which left various substrates exposed including concrete and blockwork. The surfaces were then cleaned and dried in preparation for application.

Blowerproof was then sprayed and brush applied to the soffits and walls, providing an airtight barrier in conjunction with the overall airtightness system. An airtight tape was then used in the required areas to create a continuous airtight seal.

The project was completed successfully, with Blowerproof and airtightness tape performing to the required standards on the various interior substrates.

Airtightness systems have previously only been installed in new structures, making this retrofitting project the first of its kind in the UK – but certainly not the last!

Contact us to discuss your airtightness needs

Category: Airtight Coating

Client: Cambridge University

Location: Cambridge

Surface Area: 2000m2

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