Mike & Mandy’s long term retrofit

Heating and hot water Internal walls Roofs and loft spaces Technology & Renewables Windows and doors

Since purchasing their 1960’s bungalow in 2015, the couple has changed the internal layout to include a conversion of a carport, installed an air source heat pump, solar PV and battery storage. The windows, doors, and insulation have also been improved.

Summary

Off gas – 3 months a year off grid and export 5kWh energy

EPC rating from 58D to 78C

Mould and damp on windows resolved

The Home

House Type: 1960s Bungalow
No. Bedrooms: 3
Wall Type: Cavity
Area: Wiltshire

Measures Installed

Air Source Heat Pump

Solar PV

Cavity Wall & Roof Insulation

Overview

Mike and Mandy bought their 1960s bungalow nine years ago intending it to be their forever home. The property came with gas central heating and had UPVC windows installed in the 80s. Since purchase, the couple has changed the internal layout to include a conversion of a carport into the rest of the home, installed an air source heat pump, solar PV and battery storage. The windows, doors, and insulation have been updated along the way including extracting and refilling the cavity walls, improving loft insulation, and drylining some walls and window reveals to minimise thermal bridging and tackle mould. All windows and doors were replaced with timber double-glazed units.

The rise in energy bills and environmental concerns were key drivers for Mike and Mandy along with ensuring the building used as many healthy materials as possible following a “building biology approach“.

Background

The couple, who live with their two adult children, upgraded their home in two phases. The first phase took place 2 years after they moved in and included new windows and doors, insulation, and the conversion of the carport into a liveable room. The second took place more recently in 2021-23 and involved installing a 5kW heat pump, 6.5kW solar PV and 13.5kW battery store.

Vaillant aroTHERM 5kW Air Source Heat Pump

Tesla 13.5kW Solar Battery

Mandy was keen to get a heat pump after speaking to friends who had one installed and doing her own research. The Vaillant aroTHERM heat pump, including installation cost £12,000 and the solar PV was £5,000. A further 13.5kW Tesla battery storage was installed at a cost of £9,000 in 2023.

The couple used the Renewable Heat Incentive Scheme which means over seven years they will receive £1,000 a year from the government scheme as their heat source solely uses renewable energy. Because of energy prices going up the payback period for PV is decreasing considerably.

Assessment

Mike and Mandy completed their own thermal imaging survey, hiring equipment from Climate Friendly Bradford on Avon. The survey confirmed what they already suspected about slumped insulation in their loft and saw gaps throughout. No other formal assessment was completed; however, a new EPC was produced after the works were done.

They would be interested in doing the thermal imaging again to compare and see if it’s worth drylining the extension.

The Challenge

The family were met with several challenges, some of which they were able to rectify with the second refurb. For instance, the doors that were fitted in the first phase were aluminium framed, which eventually caused condensation to build up and damaged the bamboo flooring – which was installed throughout the house at the same time. This was replaced with tiles in the second phase.

They also had a log burner installed in the 1^st phase to heat the property; however, they have stopped using it as they can find a non-pollutant fuel source and now solely use the heat pump.

Further frustrations arose during the solar PV installation. The energy distributor, SSEN had to complete a witness statement to determine that it can’t export more than 5kW (the maximum allowed for SSEN customers). This took longer than expected and unfortunately meant it was 12 months before Mike and Mandy could export solar and start generating income.

Getting used to the heat pump was one of the most challenging factors to overcome. If all four family members showered in the morning, then the hot water cylinder was fully drained. The system prioritised hot water over space heating, so often there was no heating on cold days when this happened. This was due to the system being set up using many default settings. After contacting Vaillant, Mike re-set the system, so that now hot water and heating have a more equal split and the problems encountered previously have largely gone. It highlights the importance of having the system set up to meet your expectations and needs.

The heat controls also take some getting used to, quite often the family must ignore what the thermostat says and turn it up until they feel comfortable.

Over summer the heat pump goes off for heating and hot water comes either from the heat pump or directly via the solar instead.

Unfortunately, they couldn’t insulate the rear garden room, a 1980s extension, as there is not enough external wall to dryline it. This is now the coldest room in winter, and they are thinking about adding insulation in the future. However, a problem with condensation in this room has been largely eradicated by using a dehumidifier for a few hours in the daytime, which has resulted in all condensation being removed, even overnight. The room also feels much warmer than before.

Mike said, if they were to do it again now, there are parts they would do it differently. They would have installed one door in the 1980s extension instead of two, to reduce the opening size and add internal wall insulation throughout the whole bungalow – because they can’t fill the wall cavities completely due to big, concrete lintel placement.

He also said the bathroom ventilation could have been better combined with not fully tiling the whole room, as mould builds up on the tiles regularly. A dual-fuel radiator was planned but couldn’t be installed at the time. This would allow for the radiator to work on an immersion independently of the main heating system which would allow for greater flexibility. In due course, this will be changed.

Results

The EPC has increased at each stage, from 58D when purchased, to 68D after the first refurb and it now stands at 78C.

Drylining the walls and windows has removed mould issues, however, some of the windows did have gaps around the frames, which had been sealed against the rain but not filled to avoid cold bridging – they wish that that they had overseen this and the gaps had been filled correctly.

The installation of the PV panels and battery has meant that for three months of the year, they are living off grid and even earning money by selling surplus solar back to the grid. They have noticed a warmer and more comfortable home during the colder months.