Rocksilk® Flexible Slab achieves fire resistance ‘first’

By Knauf Insulation UK & Ireland
December 05, 2022

Knauf Insulation’s Rocksilk® Flexible Slab is the first Mineral Wool insulation solution in the UK to have been tested to provide one hour of fire resistance to EN 1365 at both 400mm and 600mm centre widths within the separating floor of a loft conversion.

“Insulation is critical in providing fire resistance within the separating floor of a loft conversion, but other manufacturers have only tested their products for this application at one centre width – 400mm,” said Luke Davies, Product Manager – Rock Mineral Wool, at Knauf Insulation. “Our product is the only one in the UK to also be tested to provide one hour of fire resistance within joists of 600mm centre widths, which will give homeowners reassurance that it will perform as expected if a fire does occur.”  

“One hour is double the fire resistance stipulated by the building regulations, giving residents valuable extra time to detect the fire and escape.”  

Rocksilk® Flexible Slab is a non-combustible, Rock Mineral Wool product with the best possible Euroclass A1 reaction to fire classification. It is designed to compartmentalise the building and preserve the escape routes by resisting and preventing the passage of fire and heat from its source to the other side of the building element. 

Thanks to its all-round performance, Rocksilk® Flexible Slab is a multi-application product. So, in addition to providing fire resistance in separating floors, it is also suitable for use in other floor types, as well as roofs, walls and partitions built using a variety of different construction methods.

As with all Knauf Insulation Mineral Wool products, they are easy to install correctly. Slabs are flexible on all four sides so friction fit to the building elements, as well as being able to adapt to imperfections in construction and knit together at the joints. All of which means it’s easy to get a good fit which helps to eliminate unintended air gaps that reduce performance.  

A new detailed installation guide has been created to accompany the product with clear and simple advice to installers for a wide range of applications and scenarios. 

Rocksilk® Flexible Slab is 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. 

For more information about Rocksilk® Flexible Slab visit