Low-Rise Non-Traditional Housing, Derbyshire

Project Overview

Background

Rykneld Homes and Permarock have a long-standing working relationship, having collaborated on numerous decarbonisation retrofit projects in the East Midlands and Northern England. Operating on behalf of North East Derbyshire District Council, it is responsible for the management, maintenance and improvement of around 7,600 properties. 

This project focused on around 80 older homes in Sheffield, which featured a mix of non-traditional / archetypes, mostly based on precast reinforced concrete. These included Airey, REEMA, Wates and Unity. These designs are typically hard to keep warm because they retain heat very poorly. Certain designs also permit significant air movement, leading to cold draughts and higher running costs. 

Brief

The purpose of the scheme was, first, to assess the properties according to best practice and in line with the requirements set out in the PAS standards. Then, second, the team would design and install measures to improve the homes’ energy efficiency. It was determined that an external wall insulation (EWI) system – comprising insulation boards and an attractive render – would enhance the properties’ thermal performance, their airtightness and their outward appearance. 

Design and Specification:

For this scheme, the client chose the Permarock EPS Premium system, which features graphite-enhanced polystyrene insulation boards, together with a decorative, weather-resistant render. The whole stakeholder team agreed on the colour selections. 

The variety of substrates made it especially important that systems were designed and installed after a rigorous process of inspection and testing. This included the completion of pull-out tests on the substrates, which spanned a range of non-traditional archetypes. 

Working with the client and its chosen Trustmark-registered installer, Permarock technical staff helped to identify the necessary remedial works that had to precede the EWI installation. The team developed designs and detailing to accommodate the various archetypes without giving rise to thermal-bridging risks, and provided project-specific training to the Retrofit Installer’s operatives.  

System Characteristics

Permarock EPS Premium is a lightweight insulation system based on expanded polystyrene and graphite particles. It is suitable for both new-build and refurbishment projects, and can be used to create highly energy-efficient properties. It can be applied in different thicknesses, depending upon the level of insulation required. In this case, the system comprised 90 mm of Permarock EPS Premium insulation in most areas, together with either Permarock Dry Dash or Permarock Brick Effect Render. 

Permarock Dry Dash comprises pre-washed and screened dashing aggregates, which – as standard – can be supplied in 32 different types and colours. They are used in conjunction with Permarock Dashing Mortar which is available in 6 standard colours. However, special colours and aggregate mixes can be supplied to special order. The render system itself is hardwearing and is supplied as a pre-batched and pre-coloured dry-powder premix that requires only mixing with clean water on site. 

Permarock Brick Effect Render (BER) is also supplied pre-batched. It is based on a self-coloured polymer-modified cement-based render and can be used to achieve metric or imperial brick sizes, any bond pattern and non-standard patterns and effects. It is available in 9 standard colours but other colours can be produced to special order. 

In some areas, the specification called for 60 mm of EPS 200 Insulation – again, a lightweight system based on expanded polystyrene. The Permarock system for the main walls was complemented with a Permarock Plinth system below the level of the DPC. The system – which comprised Permarock EPS insulation panels (200 mm) and a bituminous waterproof coating – ensured compliance with the demands of PAS 2035 by minimising the risks of cold-bridging at this point. It also produced a neat, contrasting finish at the base of the external facade. The plinth system provides at least 75% of the thermal resistance of the main wall EWI system. 

Installation

The installation was completed on time and on budget in March 2025. To aid progress, Permarock technical staff provided valuable support throughout the project’s duration. This included making regular site visits and providing ongoing support via email and telephone. 

Result:

The project achieved all its stated objectives. 

The insulated render system helped to improved the appearance of the neighbourhood and greatly improved the thermal performance of the various properties, achieving the design target U-value of 0.29w/m2K. As a results, residents have reported substantial improvements to the warmth and comfort of their homes, and significant savings on their energy bills. 

Permarock also ensured that all works were supported by a 25-year guarantee backed by SWIGA. 

Client
Rykneld Homes
Specifier
Sustainable Building Services (UK) Ltd
Substrate
Precast concrete (multiple archetypes)
System
Permarock EPS Premium External Wall Insulation Systems
Finish 1
Permarock Dry Dash
Finish 2
Permarock Brick Effect Render