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INCA Case Study: Derby Tank Houses


Derby Tank Houses

Project Type: Refurbishment

Building Type: Low Rise, Residential

Architect: N/A

System Designer: Wetherby Building Solutions

Installer: Westville Group

System & Finish: Wetherby Epsiwall

U-value Before: 1.10 W/m2k

U-value Achieved: 0.27 W/m2k

CLIENT: Derby City Council & Derby Homes

DURATION: 8 Months

SUMMARY OF WORKS: EWI installation to unique war homes.

Located just off the ring road near Spider Island is one of Derby’s oldest council estates. Built around the Second World War to address a housing shortage, this estate has over 200 unique homes. Each property is unusual because they were constructed using cast iron panels covered in cement-based enamel, earning them the nickname – ‘The Tank Houses’.

In 2022 Derby City Council was awarded funding from the Social Housing Decarbonisation Fund to help transform parts of its housing stock. The primary objective was to make eligible homes more energy efficient and reduce their carbon emissions, assisting residents to lower their energy costs. Discussions occurred, and the tank houses were highlighted as primary candidates for significant upgrades. These would include External Wall Insulation alongside new windows and doors.

Following the allocation, the council’s housing division, Derby Homes, was responsible for coordinating the project and appointing their chosen contractors to undertake the transformations on what would initially be phase 1. This comprised of 80 homes, with work set to commence in Autumn 2022.

Westville was awarded the contract for the project based on their expertise and previous project experience in this area.


Work commenced on these cast-iron homes, considered to be Derby’s oldest, in 2022. Constructed just before and after the Second World War, they were built using pre-formed cast iron as this was the quickest and easiest way to get them assembled and lived in. However, this construction proved to be a real challenge as fitting EWI to cast iron walls that were 10mm thick was definitely not the norm.

Following consultation, a method was devised, which included pre-drilling pilot holes through the Cast iron and then inserting self-tapping fixings through the EPS Insulation board and into the pilot holes. This proved to be a very effective method of fixing – the overall system comprising of 90 mm Enhanced EPS Insulation Boards and Wetherby Epsiwall.

With the insulation installed, a layer of Alkali resistant scrim cloth was incorporated into Heck K&A Scrim adhesive. A second layer of scrim adhesive was then applied and smoothed off to achieve a smooth flat surface ready to receive the final finishing coat of 1.5mm render. This was then decorated with a warm cream-tone exterior contrasted with an attractive red brick effect finish.


The U-Value of the properties refurbished was 1.10

  • pre-insulation and is now 0.27. A significant reduction.
  • Interstitial Condensation and Evaporation were above 210 per month GC during the winter months, and this has now reduced to 0.00 following the EWI Installation.
  • EPC ratings for each property have improved by two levels, saving energy and reducing carbon emissions.
  • Aesthetically, a total transformation of the properties can be seen, and residents are delighted with the results.


Following the work done on the ‘Tank Houses’, the total estimated energy bill savings was around £43,200 per year, that’s an average saving of £540 per household! *

Phase 1 alone will save an incredible 72.8 tonnes of CO2 from entering the atmosphere each year. That mitigates 14 homes’ yearly electricity use, helping reduce demand on the national grid. **

Figures displayed have been calculated from the following sources:

* Energy Savings Trust – https://energysavingtrust.org.uk/advice/solid-wall-insulation/

** Greenhouse Gas Equivalencies Calculator: https://www.epa.gov/energy/greenhouse-gas-equivalencies-calculator

In post-satisfaction surveys sent out by Westville, a feedback score of 96% was achieved. Everyone was overwhelmed by the transformation of their home visually, but the vast improvement was in their heating bills, with everyone reporting a significant reduction.

Derby Homes were extremely proud of the project, resulting in Westville being awarded the contract for phase 2, which will start in late summer 2023.

“My electric bill has been reduced by £4 per day.”

D Clifton – Mellor St.

“Very happy with how my house looks. I hardly have the heating on now.”

R Drayton – Turner St.

“Very impressed with the communication I received from the office scheduling around my work commitments.”

M Morrison – Turner St

“Very happy with how my house looks. I hardly have the heating on now.”

R Drayton

Turner St.

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