Hugo and Mary’s House Extension with a Heat Pump

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Hugo and Mary’s experience extending their Victorian property with insulation, glazing and an air source heat pump.

Summary

Improved Temperature Comfort

Damp and Mould Removed

Triple Glazing

Switched to Heat Pump

Off gas

The Home

House Type: Victorian Terrace
No. Of bedrooms: 3
Wall Type: Solid wall
Space: 130 square metres
Location: Easton, Bristol

“We’ve always loved the idea of a passive house. But the carbon footprint and the cost of a new building did not make sense to us, especially when there are so many beautiful houses around that are just waiting for some TLC. Our retrofit brought us a very unique, tailored and beautiful home that is matching our needs perfectly, keeping us warm in winter and cool in summer.”
– Hugo & Mary

Overview

Buying their Victorian terraced house in 2020, Hugo and Mary wanted to create an efficient home that could stand the test of time. By making some large and small changes, they were able to reduce their reliance on electricity and fossil fuels.

Background

Hugo and Mary were motivated by a desire to put their stamp on their forever-home. Both keen on interior design and technically minded, they wanted a project which could fulfil their need for an energy-efficient home and look beautiful at the same time. The terraced house was riddled with damp and mould, due to historic mishaps with incorrect insulation and ventilation in the property.

Assessment

The first issue which Mary and Hugo had to solve was the prevalent damp and mould. So-called ‘solutions’ aimed to cover-up the mould, rather than eradicate the cause. Becoming frustrated with this outlook, Hugo and Mary investigated recalibrating the conditions inside the house which were causing the issues; looking at the insulation quality and the ventilation strategy of the building, as a whole.

Following advice from Dan from BSB, Hugo and Mary decided to remove the plaster entirely, re-insulate with wood-fibre and other eco-friendly materials and replaster with lime and hemp. Bristol Sustainable Builders (BSB) were ideal for this approach, understanding the nuances of the building type, and how the heating strategy for the house was designed to work. They also gave friendly instruction for the DIY bits in the front rooms. Simon from Calch Cymru also took on part of the indoor lime plaster.

The assessment for their heat pump happened at a later stage, following the completion of the structural work for the extension.

The Challenge

Self-managing a home project is not always smooth sailing.

Along the way, Hugo and Mary encountered a handful of challenges. These bumps in the road can be attributed to many factors; using bespoke home solutions can also create bespoke problems. In their bathroom renovation, mishaps with communications from the installers meant that there were surprises – such as cost changes, the impacts of lead times and knock-on effects of a shifting timeline.

Another point of contention was their party-wall agreement. This agreement helps protect neighbours and property owners when developing a property close to a boundary wall. With Hugo and Mary’s extension, they took care to comply with their agreement due to the terraced houses being close together. This does add an extra cost but ultimately is worth it to prevent the ‘headache’ of any disagreements.

Heat pumps are optimised when they’re installed for the best efficiency possible – the higher the COP score, the better the efficiency. For example, if a heat pump has a COP of 2, that means it is heating your home at 200% efficiency. When Hugo and Mary’s pump was installed in 2023, they were getting a COP of about 2.75. Aiming for a higher score, Hugo was able to research and find out how to make small alterations to improve that score. Tinkering with the heat pump settings himself, Hugo was able to bring the COP score to above 3 in March and April 2025.

Lastly, the level of decision-making was challenging during this home project. Some people opt to employ Project Managers to oversee the minor and major decisions that come with communicating with lots of trades professionals. Choosing a manager who aligns with your vision for your home is essential to alleviate any stress that self-managing may cause. However, Hugo and Mary with their enthusiasm and aptitude for technical understanding chose to self-manage. This ultimately paid off for them as they could choose every detail of their renovation but left them susceptible to decision-fatigue.

Solutions

Air source heat pump: Vaillant AroTherm Plus
Cork and wood fibre internal wall insulation, 60mm to avoid condensation
Wood fibre board external wall insulation at the back of the house, over pebble dash
Heated underfloor system
Heated skirting boards
Triple-glazed windows throughout the new parts of the house
Lime and hemp plaster internally

Results

As they commenced works in 2020, straight after buying the property, there aren’t previous energy costings to compare to – however, the results speak for themselves.

The central heating, powered by the heat pump, maintains a constant comfy temperature inside the house – which Hugo and Mary say is comfortable year-round. Last year (2024) they consumed 5200kWh of electricity and 0kWh of gas.

Their energy costs are about £100 per month, which is sitting under average for a home of their size – with an extension. They also use heat pump specific tariffs like Agile Octopus – using ‘Octopus Cosy’ rates in the wintertime and switching tariffs for lower costs when it suits them. They can also adjust the heat pump to run during lower-cost periods. Being agile in the energy market comes as an advantage when costs are variable.

Mary and Hugo also had an energy tracing done – aiming to check their insulation efforts for any cold-spots. The thermal imaging camera identified that the insulation was effective in maintaining a consistent internal temperature, however the pipes leading from the heat pump were a potential leak area. It was affirming for them to see the work was good quality.

What’s next for Hugo and Mary? Having completed the original works and extension, the young family are enjoying their cosy home with no big plans on the horizon.