Knauf Insulation launches BBA certified solution for partially filled masonry cavities

By Knauf Insulation UK & Ireland
May 03, 2022

Knauf Insulation has earned an additional BBA certificate for its Rocksilk® RainScreen Slab range – a new solution for partially filled masonry cavities.

Rocksilk® RainScreen Slab is now certified for use in masonry cavities in both high-rise rainscreen façades and domestic low-rise buildings situated in very severe exposure zones. The BBA certificate means that it complies with building regulations that state that insulation used in partially filled masonry cavities must have third-party accreditation.

“Our Rocksilk® RainScreen Slab is already BBA certified for the broadest range of build-ups and thicknesses of any rainscreen solution on the market,” explained Luke Davies, Rock Mineral Wool Product Manager at Knauf Insulation. “This latest addition to the range means that architects and specifiers benefit from the simplicity of using just one product, even if there are different build-ups within the project”.

The product is suitable for use with all types of masonry cavities including blockwork or reinforced concrete substrates with brick, blockwork or natural stone façades.

It is also non-combustible with the best possible Euroclass A1 reaction to fire classification. This means it complies with building regulations that ban the use of combustible insulation on buildings over 18m tall in England and Wales, and restrict their use on most buildings over 11m in Scotland.

With a thermal conductivity of 0.034W/mK, Rocksilk® RainScreen Slab at 455mm is available in thicknesses between 50mm and 220mm. The slabs are designed to interlock to prevent unintended gaps that lead to air leakage and lower thermal performance.

Rocksilk® RainScreen Slab is manufactured with a water repellent additive that preserves its integrity while it is exposed during construction. It has also been wind load tested by the Building Research Establishment to a maximum design pressure of 3,600Pa or 76m/s – the equivalent of a category 5 hurricane.  

Like all Knauf Insulation products, Rocksilk® RainScreen Slab is easy to install correctly. It has a width of 455mm to suit standard centres for installation between wall ties or brick restraint systems. Slabs are robust so they can be manoeuvred into place while maintaining the flexibility required to adapt to minor imperfections in the substrate.

Lastly, Rocksilk® RainScreen Slab is manufactured using ECOSE® Technology, Knauf Insulation’s unique bio-based binder, which contains no added formaldehyde or phenol. Mineral Wool insulation made with ECOSE® Technology is more environmentally friendly than insulation made using traditional oil-based binders, as it is 70% less energy intensive to manufacture. The product is soft to touch, easy to handle, and generates low levels of dust and VOCs.

For further information about Rocksilk® RainScreen Slab or to download the supporting material including our new installation guide, visit