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12 St Stephen’s Close:

Energy efficient retrofit and extension to 1960’s property.


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Age/Period: 1960’s
Type: Detached 4 bed
Years in residence: 2
No. Bedrooms: 4
Construction: Ashlar stone faced cavity wall construction
Area: Lansdown Road
Status: Conservation area

Key Features

Double glazed windows and doors
Internal wall, floor and loft insulation improvements
Solar Photovoltaics
Battery energy storage
Positive pressure ventilation system
Smart home heating and appliances
Octopus Agile


Having lived in a Georgian terrace on Rivers Street for some years Anne and Charlie purchased their home in St Stephen’s Close keen to live in a comfortable energy efficient environment. Prior to moving in they knew how they intended to improve and use the space this lovely positioned property offered and employed a local architect Esmond Murray to assist in putting their vision through planning and into practice.

From the purchase of the property in April 2020 until moving into the finished piece in November 2021, the build took 11months and Anne and Charlie are understandably delighted. Self-confessed energy geeks the two have found great joy in making the most of their onsite generated electricity and trying to minimise energy costs.


Double glazed windows and doors

With large south facing windows and bifold doors the property benefits from significant solar gain throughout the year, whilst heat loss is reduced through the use of high performance argon filled double glazed units. A combination of UPVC windows and aluminium bifold doors offered Anne and Charlie cost effective energy efficient solutions that eliminate the cold draughts that had haunted them at their Rivers Street property.

Internal blinds within the glazed units help to reduce unwanted solar gain and overheating in our increasingly warm summers.

Retrofit insulation

A significant effort was made during the refurbishment of the property to try and improve the thermal performance of the building fabric. This included the application of PIR insulated (40mm) dry walling throughout, the lifting and insulating of all suspended floors with 75mm of Celotex between the joists and the insulation of the loft with over 450mm of mineral wool. Access and use of the loft was retained with loft legs which Charlie and Anne would recommend.

Solar PV and Battery

The house benefits from a new Solax 4.9kWp south facing solar array which feeds a Solax 3.6kW hybrid inverter connected to a 5.8kWh battery energy storage system, again Solax. The system works extremely well thanks in part to the easy app interface and Anne and Charlie’s attentiveness, who redirect excess generation to points of consumption such as their car chargers through smart plugs and well timed operation of appliances.

Over the course of the two years since installation Charlie and Anne’s solar array has generated over 9MWh of electricity with Charlie and Anne estimating savings of nearly £3,000.

Positive pressure ventilation system

A positive pressure ventilation system which blows in preheated air through the house. Eliminating the need to install windows and doors with trickle vents, reducing heat loss by infiltration and unwanted draughts. The positive pressure ventilation system is also effective at reducing condensation risk and can is a simple retrofit option in a two storey build without any of the duct work required with a whole house MVHR system.

Smart Home Heating and Appliances

As a couple living in a 4 bedroom house Charlie and Anne were very mindful that there would be spaces in the house which would have minimal occupation through much of the year. As a result, they opted to invest in zonal heating with smart thermostatic controls which they can programme. The result is a system that heats only the occupied areas of the house.

This is also the approach that Anne and Charlie have taken with their car charging set up which again is very economical and adaptable based on the use of smart plugs to control 3kW chargers.

Octopus Agile

For any budding energy geeks, Charlie and Anne would highly recommend Octopus Agile. This dynamic energy tariff sets rates by the half hour a day in advance with rates sometimes dropping below zero. Timing their consumption and the charging of their battery to match these negative or low tariffs Charlie and Anne hope to reduce costs and lower the carbon intensity of their grid consumed electricity.

Other Opportunities

During the retrofit Anne and Charlie decided against a large rainwater harvesting tank and pump at the rear of the property due to the cost of installation and potential difficulties with maintenance. They are happy with this decision but Charlie admitted to being regretful at not installing solar thermal on a west facing roof elevation.

In the end though the couple are comfortable, warm and pay less for heating than an average house and have reduced car running costs with minimal amounts spent on petrol. Charlie and Anne are very happy with the measures they have taken.