Middlewood Locks, Manchester

Middlewood Locks is a prestigious 25-acre mixed-use regeneration scheme of Salford’s canal district. The first development phase included the construction of Quarry, an eight-storey building combining ground floor commercial space, luxury apartments and an undercroft car park for residents. 

It was the insulation for this car park that threw up a challenge for sub-contractor Horbury Building Systems. A complex underdrawing method had been specified, comprising the installation of timber battens, non-combustible mineral wool insulation and a separate soffit insulation over the top. Installation would be extremely labour-intensive, so Horbury Building Systems consulted Knauf Insulation about whether it could provide an alternative that would meet the thermal performance and fire safety requirements, but also be easy to install. 

Knauf Insulation’s Technical Support Team reviewed the specification and recommended 185mm Rocksilk® Soffit Linerboard Extra to achieve the required 0.18 W/m2K U-value.  

Rocksilk® Soffit Linerboard Extra is a Rock Mineral Wool insulation slab bonded to a 6mm off-white weather resistant facing board which provides a two-in-one aesthetic and thermal solution. It has a low thermal conductivity of just 0.034 W/mK and is designed for use as an insulated underlining solution in semi-exposed environments. The off-white cementitious particle board reflects light which makes it ideally suited for use in car parks. 

As well as thermal performance, Rocksilk® Soffit Linerboard Extra is non-combustible. It has the best possible Euroclass A1 reaction to fire classification, so it will not contribute to the development or spread of a fire should it occur. This is important because car parks can contain large quantities of a potential propellant – petrol. So the insulation will help to ensure the fire safety of the rest of the building.   

Rocksilk® Soffit Linerboard Extra also has good sound absorption characteristics so it provides high levels of sound reduction. This reduces noise from the car park, minimising disruption for the people living and working in the premises above. 

As well as meeting the specification, Rocksilk® Soffit Linerboard Extra has been enhanced to add rigidity and is easy to install. The board is simply placed onto the concrete soffit and fixed into position with five drillscrews. This reduced the installation method from three separate phases to just one, saving Horbury Building Systems time and associated labour costs. 

Stephen Hampshire, Contracts Manager at Horbury Building Systems said: “We found the panels easy to install. Firstly, we marked and drilled the fixing points at bench level. Next, we held the panels in place to the underside of the concrete – although the panels are lightweight ‘this is a two-handed operation’ – then we drilled through and fixed.”  

“We took care in lining the panels together when installing it against the soffit and with some minor tweaking up and down we got a nice flush finish.” 

Being able to align the panels exactly is not only important for ensuring a good finish. It also means that the slabs will butt tightly together, reducing unintended air gaps which can reduce thermal, fire safety and acoustic performance.  

The insulation was supplied to the Middlewood Locks construction site by distributor Galaxy Insulation.  

Thanks to Knauf Insulation’s Rocksilk® Soffit Linerboard Extra, the underlining of the car park at Middlewood Locks was easy to install, is aesthetically pleasing, and provides complete thermal, fire safety and acoustic performance.