INCA Case Study: Ashby Point, Tonbridge

Ashby Point, Tonbridge is a block of flats set close to Tonbridge town centre. It is a seven-storey steel framed building that features balconies and 3 different cladding materials. The ground floor is brick-built and the levels above it were originally cladded in EPS insulated render system which incorporated a timber cladding panels.

In 2021, the owner, Town and Country housing, commissioned a re-insulation and recladding project because the existing system was found to have failed. The brief required that the replacement system should replicate the colours and appearance of the original design and, given the height of the building – over 11 metres – it would also need to be fire-safe.

Equan’s was appointed as main contractor and PJ Mear selected as the specialist installer.

Specification and Installation:

The replacement of the old EPS insulation system began after the completion of remedial works to the steel frame. Water ingress had led to localised problems, but the fire safety aspect was ultimately the decisive decision to remediated 2800 M2 of External wall insulation replacement comprising of three different Wetherby Silicone 1.5mm colours.

The architect, Martin Arnold, specified a system comprising of Wetherby Mineral Fibre insulation in various thicknesses 180mm and 80mm, together with Wetherby’s silicone Finish. PJ Mear took responsibility for applying the EWI system and the RCM Y-Wall sheathing board, plus all the associated adaptations.

On the top floor balcony areas, 180mm dual density rockwool insulation boards were used, installed beneath the self-cleaning silicone finish. This was supplied in a special colour – S1000 light grey – to match the appearance of the original. In all, this system was applied to 1800 m² of the walls, with 900 m2 of the darker grey S4000 with 100 m2 of R90B blue applied to the double balconies at the front of the block.   

Design / Technical Challenges

Ashby’s Point was a challenging project, incorporating full replacement of EWI in conjunction with cladding panels and new aluminium balconies to attain an A1 fire system and subsequently EWS1 certificate. The building is a full SFS structure 7storey block with various projecting and inset balconies, roofing elements and an internal floating courtyard above the under-croft carpark.

The initial specification of a cavity system proved unsuitable and impractical therefore a redesign had to be carried out by Martin Arnold with input from PJ Mear to provide a direst fix system that achieved a better U Value and was more compatible with the superstructure of the existing building.

Results:

Below is the full through wall build-up of the system, the U value this achieves was U = 0.15 W/(m²K), meaning it almost doubled the minimum required value of U = 0.28 W/(m²K).

• Wetherby Silicone Render 0.0100 0.532 0.0188
• Wetherby Stone Wool Insulation Board 0.1800 0.036 5.0000
• Fixings Plastic insulation anchors No./m²: 8/m² 0.500
• Fixings equivalent diameter: 0.01 m Air gaps Level 1: dU” = 0.01 W/(m²K)
• BS EN 12524 Cement-bonded particleboard 0.0120 0.230 0.0522 4
• Unventilated Airspace BR 443 Normal cavity – 25 mm unventilated 0.0250 0.139 0.1799
• Light steel-frame consisting of: 0.0750 ø 0.121 0.6181 5a
• Flexi RWA 45 Rockwool (75mm) 600mm wide 99.83 % 0.038
• Air gaps Level 1: dU” = 0.01 W/(m²K) 5b BS EN 12524
• Steel 00.17 % 50.000 – 6 Own catalogue
• VCL 0.0001 0.330 0.0004 7 BS EN 12524
• Gypsum plasterboard 0.0150 0.250 0.0600 8 BS EN 12524
• Gypsum plasterboard 0.0150 0.250 0.0600 Rsi

Stakeholder Feedback

“While we did not work directly with PJ Mears, our feedback from the Clerk of Works was that the works were well planned and to a high standard.  When carrying our regular inspections with the client (building owner), we were jointly very happy with the quality of finish and final aesthetic of the project.  The render in particular.”

Jamie Collins, Martin Arnold

“it was a pleasure to work with PJ Mear on this innovative and complex project which introduced a number of challenges along the way. However, with Wetherby’s unique site support and brilliant customer service levels we managed to deliver the contract in-line with contractor and client expectations”.

Paul Dale, Wetherby Building Systems

PJMear have been a trustworthy and reliable partner throughout the journey, providing key input into the design and planning stage as well as ad-hoc solutions. They have facilitated a close collaboration with all the manufacturers (Wetherby, Rockwool etc) and integrated a robust ITP process to make sure all the technical specifications are meticulously followed into practice. The site management, level of quality assurance and the subsequent quality of finish was excellent and praised by both client and residents.

Chris Vasiu – EQUANS Site Manager”