INCA EWI Case Study: Thurleston Avenue, Morden

This project involved the external wall insulation retrofit of a semi-detached domestic property at 12 Thurleston Avenue, Morden, SM4 4BW.

The property’s pre-retrofit EPC rating was E48, placing it within a low energy efficiency band. The EPC identified the property as having solid brick walls, as built, with no insulation, which were recorded as a significant contributor to heat loss. The external walls were therefore assessed as a priority area for improvement.

Following a detailed assessment, external wall insulation was recommended as the most suitable retrofit measure to improve the thermal performance of the property. The aim was to reduce heat loss through the solid walls, improve internal comfort, and support a measurable improvement in the property’s overall energy efficiency.

The property was also eligible for support under the Great British Insulation Scheme (G.B.I.S), and funding was provided towards the external wall insulation works. This helped make the retrofit more accessible to the homeowner while ensuring the property benefited from a high-quality, long-term energy efficiency improvement.

The EWI system was designed by Atlas Building Materials Ltd and installed by Infinity Property Management Ltd. The works included the installation of 83 sqm of external wall insulation with a smooth render finish, together with 30 sqm of render-only works for extension part which was cavity to provide a consistent and well-presented external appearance across the property.

Additional associated works were also completed as part of the project, including a 10m roofline extension, removal of tiles from the bay window, and the installation of 11 trickle vents to support appropriate background ventilation following the improvement of the building fabric.

Prior to the works, the estimated wall U-value was approximately 2.10 W/m²K, based on the uninsulated solid wall construction. Following installation of the 100mm external wall insulation system, the achieved wall U-value is estimated at approximately 0.29 W/m²K, representing a significant improvement in the property’s thermal performance.

The installation was completed with careful attention to the existing property details, including junctions, openings, roofline interfaces, ventilation requirements, and the overall finish. This ensured the insulation system not only improved the property’s energy efficiency but also maintained a clean, durable, and visually consistent appearance.

Following completion of the external wall insulation works, the property achieved a post-retrofit EPC rating of C72. This improvement from E48 to C72 demonstrates the positive impact of the external wall insulation on the property’s overall energy performance.

The homeowner was highly satisfied with the completed project and left a 5-star Google review, commenting that the project was managed with care, communication was “impeccable”, and that they would “definitely recommend” Infinity Property Management.

To provide long-term confidence in the installation, the project was supported by a 25-year system warranty / insurance-backed guarantee, together with a 2-year workmanship warranty from Infinity Property Management Ltd.

Scope of Works

The key energy efficiency measures delivered were:

• External Wall Insulation with smooth render finish: 83 sqm
• External Walls Render-only works for extension: 30 sqm

The associated enabling and finishing works included:

• Roofline extension: 10m
• Removal of tiles from the bay window (as customer didn’t want this feature anymore)
• Installation of trickle vents: 11 units

Outcome

The project delivered a clear and measurable improvement in the property’s thermal performance, reducing heat loss through the previously uninsulated solid walls and helping to create a warmer, more comfortable, and more energy-efficient home.

The uplift from EPC E48 to C72 highlights the effectiveness of high-quality external wall insulation in improving existing solid wall housing stock. The project also demonstrates how G.B.I.S funding can support the delivery of meaningful retrofit measures, helping homeowners access long-term energy efficiency improvements.

The positive customer feedback reflects the quality of workmanship, care, communication, and project management delivered throughout the installation, making this project a strong example of a successful domestic EWI retrofit.