Project Overview:
Background:
With this scheme, Nottingham City Homes sought to upgrade two high-rise tower blocks for older residents and to provide brand-new extra care apartments and facilities as part of its ‘Building a Better Nottingham’ programme. It appointed Willmott Dixon as main contractor, and Halsall Lloyd Partnership (architect) to develop the necessary plans.
Their solution entailed recladding the two existing blocks, Woodthorpe Court & Winchester Court, which were built in 1964, and building a new extra care facility between them with communal facilities for all residents to use. The scheme was designed to offer flexible care and support to enable older residents to continue to live independently.
The Brief:
The design of the two tower blocks featured Wimpey no-fines concrete. Whilst there are generally no significant structural problems associated with this as a walling material, no-fines concrete buildings are notoriously hard to heat and are prone to condensation and dampness. They are also relatively difficult to maintain and adapt than more traditional forms, and are more prone to rain-water penetration and deterioration of the external render.
The design brief was therefore to make improvements to the energy performance and internal comfort of the buildings. This required a fabric-first approach to improving the building envelope. Extensive use of non-combustible external wall insulation (EWI) with decorative renders in a range of colours and styles was a key part of the proposed façade treatment. The works also included replacement windows throughout, upgrades to the heating system, and sprinkler systems fitted to all communal areas and apartments.
A key element of the architectural design was the creation of a faux metal rainscreen cladding effect and the use of colour. On selected walls, it called for a ‘patchwork’ of rectangular panels that would gradually transition from darker to lighter shades as the two high-rise blocks ascended. Consequently, it was important that the chosen system could be installed and finished in a way that would maintain this visual impression and provide the necessary thermal improvements.
Due to the impact of the Grenfell Tower incident, which took place within the latter part of the design phase, the reaction to fire performance of the proposed PermaRock external wall insulation system was carefully scrutinised. However, it was found to provide exactly the high degree of fire safety that the works demanded.
The Buildings:
The two existing 15-storey residential tower blocks were of in-situ concrete frame construction with Wimpey no-fines concrete walls. These were partially clad in facing brickwork and partly covered by an existing EWI system, which was failing to protect the building and showing signs of failure. The blocks had external balconies, which were to be enclosed as part of the scheme.
The Design Stage:
Following consultation with PermaRock, the project architect, HLP, selected a PermaRock Mineral Fibre EWI system. It had established that its performance met the project criteria in full and could provide the dynamic, modern appearance that the design for the buildings required. In sympathy with the parkland setting, the colour scheme evoked a sense of falling leaves.
To help meet the various technical and planning requirements, PermaRock Technical Services team worked closely with the stakeholder partners to produce the necessary specifications, visualisations, samples and detailing. PermaRock also supported the designers with U-value calculations and worked with the architect and main contractor, helping them to design the interfaces with other building elements such as windows, doors, roofs and the newly enclosed balconies.
During the ecological survey, the tower blocks were found to have bats roosting in the weepholes in the brickwork/masonry. Elements of the project therefore had to be delayed until the bats had moved on. The EWI system design was duly adapted and design details were created by PermaRock’s technical team to incorporate bird- and bat-boxes into the EWI system.
Specification and System:
The PermaRock Mineral Fibre EWI System was chosen to provide the thermal insulation for both the brick cladding and the rendered no-fines concrete walls of the two tower blocks. The system is both adhesively bonded and mechanically fixed directly to the substrate, with no cavities; a process which ensures that it can resist high wind-loading and which avoids the risk of fire spread within or behind the system.
The system is suitable for application onto all building types, including multi-storey blocks above 11 metres, where strict non-combustibility requirements must be met. The system incorporates non-combustible (Euroclass A1 to BE EN 13501-1) mineral fibre insulation boards, reinforced basecoats and a range of renders providing designers with extensive choice in colour and texture.
The EWI system was finished throughout in PermaRock SiliconeUltra K-Finish which was applied over the primed reinforcement layer in various colours. Some elevations featured a single, solid, unbroken colour while on others the decorative finish was applied in different shades with ‘feature joints' to create the panellised appearance originally envisaged in the cladding design.
PermaRock SiliconeUltra K-Finish is a lightweight, nano-quartz based render that is water-repellent and demonstrates excellent water vapour permeability. It is through-coloured with a self-cleaning effect that resists the accumulation of airborne pollutants and dirt, helping to maintain a clean, bright appearance even in challenging urban environments. Similarly, biocidal preservatives help to resist the growth of unsightly moss and algae. SiliconeUltra K-finish renders are available in an extensive range of colours and a choice of textures and grain sizes: 1.5 mm, 2.0 mm and 3.0 mm.
Performance: Fire Safety
The PermaRock Mineral Fibre External Wall Insulation system employed on the two tower blocks has an A2-s1,d0 Reaction to Fire classification (EN 13501-1) and is suitable for use on buildings of any building height, and in proximity to any boundary.
The system used on this scheme has been independently tested and assessed (BRE Certificate 158/12) and exhibits an assessed lifetime of at least 30 years. It is amongst only a small number of systems to be supported by a Solid Wall Insulation Guarantee Agency (SWIGA) 25-year guarantee for use on high-rise buildings.
Performance: Thermal Insulation & Sustainability
The thermal design for the towers required the walls to achieve a U-value not exceeding 0.30 W/m2K. PermaRock dual density mineral fibre insulation – with a thermal conductivity of 0.036 W/mK - was used at 90 mm and 110 mm on the different wall types to achieve this.
An independent whole-life environmental assessment of the PermaRock Mineral Fibre EWI system has shown that the system achieves an Ecopoints score of 0.10/m2 – achieving an ‘Excellent’ rating. It can assist in achieving maximum credits under BREEAM 2011 credit Mat 04 – Insulation.
Result:
Throughout the scheme, PermaRock Technical Services provided ongoing support to the design team, the main contractor, the client and to the specialist subcontractor appointed to install the PermaRock system.
The wider scheme also included the work undertaken on the new-build element, known as Winwood Heights. It yielded an extremely impressive transformation, upgrading the existing flats and creating a further 44 high-quality apartments, all with a zero-defect record.
The project was widely appreciated by residents – both new and existing – and it went on to secure a host of awards:
- Inside Housing Development Awards 2021: ‘Best Older People’s Housing Development (rural and suburban)’ category
- RICS Social Impact Award 2020 East Midlands (residential category)
- Building Communities Awards 2020: Project of the Year (over £3m category)
- East Midlands Awards 2019: East Midlands Scheme of the Year
- fbe East Midlands Chairman’s Annual Dinner: Chairman’s Award for Project of the Year