Located on the former BBC site, Circle Square in Manchester aims to create a vibrant neighbourhood comprising city living apartments, prime office, retail and leisure space.

Phase two of the development saw the construction of No’s 5 to 8, four buildings totalling 677 luxury flats with private dining, resident lounge, gym and cinema, as well as commercial space.

Specification requirements

FK Group were appointed to design and install a bespoke façade solution which meant they were responsible for specifying the insulation. There were three main performance factors that needed to be considered.

Firstly, the insulation had to be non-combustible to ensure compliance with building regulations in England and Wales, which ban the use of combustible materials on the external walls of certain buildings over 18m tall.

The second consideration was thermal performance.

“When you’re designing a bespoke façade solution, accurate thermal modelling is essential because there are so many variables that can affect its energy efficiency,” explained Ben Hufton, Associate Design Director of FK Group:

“One of the reasons we work with Knauf Insulation so much is because of their technical support. They always conduct 3D U-value calculations for rainscreen façade projects, so we know the insulation will deliver the performance we need to achieve.”

This enhanced level of accuracy is one of the main benefits of 3D U-value calculations over other calculation methods, because it ensures a building’s real world thermal performance matches its initial design.

To achieve the required U-value of 0.28 W/m2K, the Knauf Insulation Technical Support Team recommended 200mm Rocksilk® RainScreen Slab for the external cavity. This has a thermal conductivity of just 0.034W/mK.

Rocksilk® RainScreen Slab is manufactured from Rock Mineral Wool and is BBA certified for use in high rise buildings for the broadest range of build-ups of any rainscreen solution on the market. It is also non-combustible with the best possible Euroclass A1 reaction to fire classification. This means it will not contribute to the development or spread of fire should it occur.

The final specification factor was acoustic performance due to the site’s busy city centre location.

FK Group conducted offsite acoustic tests to ensure that the build-up met the requirements of Approved Document E. The Mineral Wool insulation contributes significantly to the acoustic performance of the build-up thanks to its open structure. Sound waves are trapped between the individual strands of Mineral Wool and turned into heat energy. This will help to reduce noise from surrounding roads, ensuring residents can enjoy peaceful homes.

Other performance factors

As it has been developed for external applications, Rocksilk® RainScreen Slab contains a water repellent additive which is combined with a fibre matrix that promotes run-off. This ensures it can resist moisture ingress whilst maintaining its excellent vapour permeability. The physical characteristics of the fibres are unaltered if they get wet. Therefore, the thermal properties of Rocksilk® RainScreen Slab are not affected by exposure to moisture and the product will perform as expected once it has dried out.

The product is easy to install correctly thanks to superior robustness and durability, allowing it to be manoeuvred easily into place. Its natural flexibility means it adapts to minor imperfections in the substrate, while slabs interlock, eliminating air leakage that could reduce thermal and acoustic performance.

Rocksilk® RainScreen Slab is also manufactured with ECOSE® Technology, Knauf Insulation’s unique bio-based binder that contains no added formaldehyde or phenol. It is made from natural raw materials that are rapidly renewable, and is 70% less energy-intensive to manufacture than traditional binder, so it is more environmentally-friendly.

Products made with ECOSE® Technology generate low levels of dust and VOCs (volatile organic compounds) and have been awarded Eurofins Indoor Air Comfort (Gold) certification.

Circle Square will give residents access to everything they need from a community district – just as Knauf Insulation’s Rocksilk® RainScreen Slab ticked all the boxes for FK Group.