Skip to main content

1980s Retrofit

Insulation, Ventilation, Solar PV, Batteries, and an Air Source Heat Pump
Download Printable Case Study (PDF)


Age/Period: 1980s
Type: 2 storey detached
Years in residence: 21
No. Bedrooms: 4
Wall type: Stone façade over breeze blocks with. cavity
Area: Widcombe

Key Features

Triple glazed windows and doors
Internal and cavity wall insulation
Loft Insulation
Draught Proofing
Mechanical Ventilation with Heat Recovery (MVHR)
Air Source Heat Pump (ASHP)
Solar PV and batteries
Energy efficient appliances and lighting


Nigel and Simone had always been environmentally conscious and an electricity monitor and more recently their smart meter display was instrumental in inspiring a number of quick win energy saving activities. However, the need to replace their old windows triggered the larger scale energy efficiency improvements on the home. Nigel and Simone had seen the Passivhaus Standard in Germany and were keen to use its principles of insulation, air tightness and controlled ventilation to make their own home greener and cheaper to heat, whilst increasing security and comfort.


Triple glazed windows and doors

Low maintenance, high performance triple glazed windows and patio doors were installed throughout the house in 2012. The triple glazing is an aluminium finish externally and wood internally and loses 65% less heat than the double glazing it
replaced. Their research showed there was little price difference between double glazed and triple glazed, so it made sense to upgrade. Simone said:

“Windows are going to last 30 to 40 years, so it’s worth choosing carefully and buying good technology”


Cavity wall insulation was installed shortly after Nigel and Simone first moved in 21 years ago and at that time, they received it at a subsidised rate and it made a noticeable difference. Subsequently many of the internal walls have been internally insulated with Marmox and Celotex panels which was screwed to the wall and then plastered over. The Marmox was used mainly in the windows reveals and in the wet rooms because it doesn’t require plaster board and forms a vapour barrier layer. The inside wall of the garage and the utility room were also insulated.

Mineral wool loft insulation was improved from a depth of 100mm to 350mm.

Practically all the ground floor has been insulated from below with Celotex insulation between the joists and multifoil insulation below to act as a vapour control barrier to reduce condensation risk. With hindsight Nigel and Simone regretted not to have done the under floor insulation at the time they undertook cosmetic renovations to the house when they first moved in as it would have been a lot easier, cost-effective and enabled all the floors to have been insulated. Pipework was also insulated throughout.

To reduce draughts, the new front door does not have a letter box, instead a self-contained letter box is fixed on the outside wall. The small roof area above the porch has been insulated with Celotex and mineral wool. This had previously been a weak area for heat loss but was easily accessed and improved.

Mechanical Ventilation & Heat Recovery

Improving the glazing and insulation has increased the air tightness of the property. After taking humidity readings in the house, it was identified that mechanical ventilation was needed to control humidity and air exchange and as a result a Vent-
Axia Mechanical Ventilation with Heat Recovery (MVHR) system was installed.

The MVHR consists of a series of insulated pipes that extract warm, stale, and moist air from the kitchen and bathrooms and pulls in fresh air from outside. The heat from the extracted air pre-heats the incoming cold air via a heat exchanger which is
92% efficient, much more efficient than opening windows where 100% of the heat is lost compared with the MVHR’s 8% loss. The MVHR also filters the air, which has been beneficial for the allergy sufferers living in the house.

Appliances and lighting

All the electrical appliances are energy efficient. The family do not own a tumble drier, prefer to dry their clothes outside whenever possible, but can also hang them up inside in winter without it creating humidity challenges due to the MVHR. Lighting throughout the house is low energy.

Solar PV and batteries

In 2018 Nigel and Simone had 14 solar PV panels installed, half facing east and half facing west, along with 4 kWh of batteries.

The combination of the solar PV and batteries means that they rarely consume electricity between May and September each year, the majority of their bill just being the standing charge.

Air Source Heat Pump

In 2019 Nigel and Simone had a 11 kW Mitsubishi EcoDan air source heat pump installed by Almondsbury Ecoheat. To make the heat pump as efficient as possible the majority of their radiators were increased in size. Nigel and Simone were very
happy with the installation which will have led to a 75% reduction in the carbon emissions of their heating and hot water compared with their previous gas boiler, and up to 90% by 2030 as the national grid decarbonises.

The house’s hot water is now timed to run daily in the early afternoon when their solar PV output is at its peak. The ASHP is remote controlled as part of the BWCE Flex Community pilot which aims to make the most efficient use of renewable energy.

They have also installed wireless Danfloss radiator valves which allow them to automatically turn individual radiators on and off on a timed basis remotely and so only heat the areas of their home that they occupy at different times of the day.

Having removed the gas boiler Nigel and Simone also replaced their gas hob with an induction hob, which is easier to clean, faster, more efficient and doesn’t pollute the house with NOX air pollution. As a result, they have been able to disconnect the gas meter and no longer have to pay a standing charge for the gas.


The house consumes 2,850 kWh/year of electricity each year compared with an average of 21,000 kWh/year energy consumed by an unrefurbished home of similar size and age, so an impressive 86% reduction.


Building Contractors: Aegis
Air Source Heat Pump:http:
MVHR – Vent Axia
Information – Green Building Forum