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) are undergoing a pioneering retrofitting project for their new headquarters. Their vision is to create an ultra-low carbon, sustainability hub that set new standards for energy use. To achieve this, they are transforming a 1930’s telephone exchange in Cambridge that will operate on 80% less energy, complete with a deep energy retrofit to the Passivhaus standard, EnerPhit.


To achieve the EnerPhit standard an improved airtightness system is 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 spray 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 required areas to provide a continuous airtight seal.

The project was completed successfully, with the combination of 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!

Category: Airtight Coating

Client: Cambridge University

Location: Cambridge

Surface Area: 2000m2

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