The Oak Cancer Centre at The Royal Marsden’s Sutton site is a state-of-the-art research and treatment facility, designed to bring the hospital’s 400-strong research team and its clinical care facility together under one roof.

Specialist brickwork contractors, Lesterose Builders, were appointed by main contractor ISG to design and build the 2,800m2 masonry façade. As a result, they were responsible for ensuring the façade complied with the relevant thermal and fire safety regulations.

The time and cost challenge

The architect’s specification named a rock mineral wool product, but when Sam O’Keefe, Commercial Manager at Lesterose Builders, tried to place the order, there were two problems. He explained: “The first issue was availability – there was an eight to ten week lead time due to materials shortages. And the second issue was cost. We discovered the original insulation manufacturer had two planned price increases, and the extended lead time and phased delivery schedule meant that the Oak Cancer Centre project would be hit by both.”

These two issues would not only delay the build but would push it significantly over budget. So Lesterose Builders needed another insulation solution.

Meeting the specification

Lesterose Builders turned to Knauf Insulation, a fellow member of the Association of Brickwork Contractors (ABC). Knauf Insulation’s sales team looked at the specification and was able to offer an equivalent – 200mm Rocksilk® RainScreen Slab.

Rocksilk® RainScreen Slab is a rock mineral wool insulation product with a thermal conductivity of just 0.034W/mK, which meant it would meet the U-value of 0.21W/m2K.

It is also non-combustible with Euroclass A1 reaction to fire classification, which means it will not contribute to the development or spread of fire should it occur. It is British Board of Agrément (BBA) certified for masonry façades at any height as well as for the broadest range of build-ups of any rainscreen solution on the market.

This meant Rocksilk® RainScreen Slab was suitable for use in the Oak Cancer Centre because it complies with building regulations that ban the use of combustible materials in the walls of relevant buildings over 18m tall.

In addition to fire safety and thermal performance, Rocksilk® RainScreen Slab offers excellent sound reduction characteristics.

Crucially, Knauf Insulation was able to meet both the schedule and cost parameters for the project.

“Once we had confirmation that Knauf Insulation could match the specification and deliver to the planned timescales and budget, it was then a case of getting the architect’s approval. This went extremely smoothly. We just made a technical submittal with the datasheets and environmental product declaration (EPD) and Rocksilk® RainScreen Slab was approved for use without any queries.”

Ease of installation

The seven-full loads of insulation were purchased through Parker Building Supplies. These were delivered to the site in eight phases in line with the schedule of works.

The product is designed to be easy to install correctly. Superior robustness and durability mean it can be manoeuvred easily into place. And unlike some competitor products, it can be installed with either face of the slab against the substrate, speeding up installation and preventing incorrect installation.

Furthermore, the natural flexibility of rock mineral wool means it adapts to minor imperfections in the substrate, while slabs knit together when tightly butted, 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 binders, 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.

Construction work is known for its challenges, particularly around budgets and schedules – but thanks to Knauf Insulation’s Rocksilk® RainScreen Slab, Lesterose Builders was able to overcome both these issues and meet the required specification factors for the Oak Cancer Centre.