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Case Study6 min read
Kooltherm K5 External Wall Board was specified as part of an innovative, large-scale whole building retrofit system installed on a social housing development in Solihull.
LOCATIONSolihull, UK
ArchitectBeattie Passive
ProductsKooltherm K5 External Wall Board
Grandy’s Croft, a low-rise block of six flats, was upgraded to meet the demanding EnerPHit Standard using a revolutionary off-site, wrap-around large scale (OWLS) retrofit solution: the Beattie Passive TCosy™.
Funded by Innovate UK through their ‘Scaling-up Retrofit Competition’, the pilot project was a collaboration between Solihull Community Housing, system designers and installers, Beattie Passive, and Passivhaus consultants and project managers, Encraft. Additional technical and tenant management support was also provided by Coventry University.
The all-in-one retrofit solution was installed around the existing building to create a highly-insulated envelope, limiting thermal bridges. Kooltherm K5 was selected as a key component of the system due to its ability to deliver premium thermal performance relative to its thickness.
"Using the Kooltherm K5 External Wall Board within our retrofit system has helped us to achieve U-values of just 0.099 W/m²K for the walls and an airtightness test result of 0.93 air changes per hour (ach) @ 50 Pa. These calculations mean that the Retrofit system easily meets Enerphit Standards".
Ron Beattie - Managing Director, Beattie Passive
Due to the level of airtightness, it was also necessary to install a Mechanical Ventilation and Heat Recovery (MVHR) system. The ductwork could not be installed inside the properties themselves, so Beattie Passive utilised their patented void around the outside of the building to incorporate the services.
Tenants remained in their homes for the duration of the project and have already been enjoying the benefits of living in a healthier, more comfortable environment. It is anticipated that their energy bills will be reduced by 85%, from £1,064 per flat to just £166 per year. Mark Pinnell, Head of Asset Management at Solihull Community Housing commented: “We have a strong commitment to improving the energy efficiency of our homes and this project makes a real contribution.”
Coventry University, in collaboration with the contractors, building owners and tenants, will be carrying out ongoing monitoring of energy usage, temperature and indoor air quality in the flats to ascertain the impact of the project.
Page updated 18/12/2025
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