The self-confessed “building bore” Judith Leary-Joyce has lived in a three-bedroom end-of-terrace house in an unassuming cul-de-sac in St Albans, Hertfordshire, since 1979. Over the years she and her husband, John, 70, have made many improvements to their “cold, dark and draughty” 1901 home, the most recent round culminating in a 75 per cent reduction in energy consumption.
In August 2020 the couple decided to pull down their large conservatory — “freezing in the winter and too hot in the summer” — and extended the footprint of their kitchen to create a more liveable space year-round. Leary-Joyce, 75, admits that she has never been much of a fan of open-plan because “it’s so easy to use too much energy”, but she was keen to improve the eco-efficiency of the home, which was so “bitterly cold” during winter that it necessitated layers of cashmere. Plus they’d wanted to install an air source heat pump, so it seemed like the ideal opportunity.
To oversee the works the couple hired an architect, who explained partway through the build that no matter how well their new extension would be insulated in preparation for the heat pump, much of the warmth would be lost through the rest of the leaky house. This was a penny-drop moment, spurring the Leary-Joyces to kick-start the process of retrofitting their home.
“We didn’t know what we didn’t know,” Leary-Joyce writes in the Beginner’s Guide to Eco Renovation, the book she wrote after the project. A retired social worker, psychotherapist and leadership coach, she was a speaker at the TEDx St Albans conference in 2023 and has built a sizeable community on social media, dishing out down-to-earth, no-nonsense, eco-conscious tips to her 44,000-strong following on Instagram (@ecorenovationhome).
“It’s often more about the questions we ask than the knowledge we have,” she says. “The moment I decided I would write the book was the day I discovered the word ‘retrofit’. I kept looking up renovation, which was giving me loads about gorgeous design but wasn’t telling me about insulation and so on. Then I discovered retrofitting and a whole world opened up.”
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The couple’s sustainability journey has boiled down to four main factors: insulation, airtightness, ventilation and breathability. None of these should be looked at in isolation, she explains from her toasty open-plan kitchen/living room with a glass of freshly squeezed carrot juice in hand.
“Most Victorian buildings are just a single brick, as ours is, and you lose something like 24 per cent [of the heat] through the walls. The idea with retrofit is that it is like a big blanket round your house, cutting out all the uncontrolled air. But then you’ve got to put back in controlled air, because it also has to move the moisture. Each family produces about 14 litres of moisture a day and it’s got to go somewhere.”
Many builders will reach for polyisocyanurate (PIR) — a cheap, common type of rigid foam insulation covered with a foil-like material that is nonbreathable, made with petrochemicals — which Leary-Joyce notes is “terrible for the environment” and “gives off volatile organic compounds [VOCs].”
When designing their extension the architect’s recommendation was to put a breathable membrane across the wall; build a stud frame to hold the insulation and put 8cm of wood fibre insulation batts (Pavaflex) into each gap in the framework. This was covered with 4cm boards of Isolair (“the wood-fibre equivalent of plasterboard”). Stuffing the Pavaflex batts (cut with a saw) into the wood frame was something the couple did themselves — “it does require an eye for perfection, because each gap means more draughts”, Leary-Joyce says. The final layer is lime plaster (ordinary plaster isn’t breathable). She recommends Lime Green Solo. Other types of sustainable insulation include a combination of recycled denim, cotton and velvet (which has been used in the Leary-Joyces’ roof), cork, hemp, sheep’s wool and Diathonite (a thermal plaster) used around the awkwardly shaped bay window in their living room.
However, PIR insulation was installed under the concrete floors in the extension. In hindsight the Leary-Joyces would have used eco-friendly alternatives to the insulation and concrete, such as hempcrete (a biocomposite); every tonne of concrete production releases one tonne of CO₂. “If your budget is limited and you live in a non-breathable house and your only option is to use PIR, that’s better than not insulating at all,” she adds.
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Particular attention was paid to minimising draughts, which can leak as much as 20 per cent of the heat created. To improve the airtightness of the new extension consideration was given to how the walls join together, ensuring there was no break between walls and the floor, fitting the windows tightly into the frame and continuing the airtight barrier.
For ventilation, single-room individual heat recovery units were installed in six rooms. Together these save 85 per cent of the heat, and are “much more effective” than trickle vents (background ventilators integrated into window frames).
“Breathability is relevant to houses built before 1930,” Leary-Joyce says. “It relates to the management of vapour in the structure of the building. When the houses were built all materials were vapour permeable, so vapour can move through them easily from both outside and inside, reducing condensation. Problems arise if a nonbreathable (non-vapour permeable) material is used alongside breathable.
“When moist air travels through the breathable material then hits again the non-breathable barrier it will condense, and over time this will cause damage to the structure and you can end up with damp and mould. So once breathable, always breathable.” From the outset if you’re working on new-builds “you need to decide either to build with modern, rigid, nonbreathable materials that block the movement of moisture altogether or go with breathable materials”.
The Leary-Joyces’ builders were not specifically eco-trained, but they were open to ideas. “There is a reason we have so many old and Victorian buildings today — the breathable system works. Because builders aren’t trained in this work, it doesn’t mean they won’t be interested. Homeowners just need to inform themselves so they can take a more active part in the work being done and share their learning with the people working for them.”
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• The ultimate guide to retrofitting your house
Other eco-upgrades include solar panels on the roof (which faces east-west), triple-glazed windows (Leary-Joyce notes that care must be taken during fitting) and Pavatex insulation underneath the suspended ground floor. The air source heat pump — a Mitsubishi Ecodan 8.5kW R32 , one of the quietest on the market — has been fitted above the roof of the extension. “We often hear complaints about [air source heat pumps]. From what I understand this is more likely to be human error. It’s new technology so not very many people are yet skilled in fitting.”
Midway through they decided to take out the chimney breast — “just a dirty great hole into the house that makes the place freezing”. She adds that their 15-month renovation took much longer than it needed to. “People need not to judge by our journey — we kept adding new bits and we were learning as we went along, working with the builders to get them to be as thorough as we could, because a lot of retrofit is about being nitpicky.” For instance, checking airtightness and making sure the insulation is really thorough.
“Last summer we did our bedroom, the final big piece of the puzzle, which we initially cut out of the thermal envelope of our home [any structure in your home that separates the air inside your home from the air outside] as I always like to sleep with the window open at night. We put a door closer on and the door was constantly closed.”
During the bedroom renovation builders pulled off the old plaster to strip back to brick and applied a Diathonite skim. “They sealed that in for breathability and attached an 8cm, rigid wood fibre board insulation, then [Green Solo] lime plaster on top of that.” This meant losing only about 10cm from the walls in the process — pretty much unnoticeable. “The carpenter beautifully built out the window reveal, you’d never spot it, but it makes the world of difference,” she says. “Even in those two years, the way of insulating has become so much easier — the retrofit [world] is moving really fast. It was a much easier job.
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• Our top tips and tricks for going green at home
“The beauty of [retrofit] is there’s no sacrifice. It’s a piece of climate action where you’ll only gain. Our EPC [energy performance certificate] rating improved from D [average] to B — and we’re warm. We can no longer just sit back and hand over responsibility. We’ve got to be informed now,” she urges.
It’s not the only benefit. One agent recently estimated that the retrofit added around £90,000 to the value of their home. “He said, ‘If you were moving this would be a special sale. We would do a weekend open house and there would be a bidding war.’”
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What we spent
• Materials for insulation £3,800
• Labour approximately £10,000
• Ventilation Heat-recovery single-room units about £500 each. We have six.
• Air source heat pump £15,000, but £7,500 of that comes back in a grant from the government.
• Overall cost of making the house energy efficient (not including the renovation, extension etc): approximately £23,000, including the air source heat pump and ventilation units.
