Guy Martin's 'House Without Bills': What a Passivhaus Retrofit Tells Us About Getting New Builds Right
A mainstream TV programme put Passivhaus retrofit in front of millions. Here is what it shows, and the one part of a house a retrofit cannot easily fix.
When Guy Martin's House Without Bills aired on Channel 4 on 9 February 2026, it put Passivhaus retrofit in front of a mainstream audience. According to the Passivhaus Trust, the 90-minute programme follows a nine-month renovation of a semi-detached house in Stretford, Greater Manchester, with the aim of driving its heating bills as low as possible.
There is plenty in it for anyone renovating. There is also a less obvious lesson for anyone building new: the part of a house that a retrofit finds hardest to change is the part a new build can get right from the start. That part is the ground floor.
What the programme covered
The Passivhaus Trust says Guy Martin works on each of the key installations at Stretford, where the project team included Passivhaus Trust members Progress in Practice, Myzsa Group and ZE Passivhaus. Homebuilding reports that over the nine months the team worked on high-performance insulation, airtight construction, upgraded windows and mechanical ventilation with heat recovery.
Along the way he visits Warksburn Old Church in Northumberland, described by the Passivhaus Trust as the world's first Passivhaus church-to-home conversion, now operating as holiday rental accommodation. It was commissioned by Anne and Alan James and undertaken by a team including Ecospheric and ZE Passivhaus. He also visits Salford University's Energy House 2.0 research lab and a flat-pack home builder on Merseyside, and shows the finished Stretford house to the Mayor of Greater Manchester, Andy Burnham. The programme was made by North One, part of the All3Media Group, and co-funded by Nesta.
Guy Martin's own advice
After the programme, Guy Martin's official website published a follow-up with his advice. In summary:
- Sort insulation, draught-proofing and ventilation first, and only then think about upgrading windows and doors.
- Treat Passive House standards as guidance even if you cannot go all the way. He calls them the gold standard.
- You can work in stages, for example insulation one year and windows the next.
- Any retrofit can be expensive, Passive House or not.
That sequence, fabric first and then the systems that depend on it, is the same logic Passivhaus applies to new buildings.
Why the floor is different
A retrofit can add insulation to walls and roofs, swap the windows and add ventilation with heat recovery, room by room and year by year. The ground floor is buried, and the foundation sits under the walls. In its guide to insulating foundations, Passive House Plus says retrofitting an insulated foundation system is practically impossible without lifting the whole building. The options it lists are limited: digging out the ground floor to add insulation, or extending external insulation below ground level. It also describes the wall-floor junction as one of the notoriously tricky spots that must be detailed and insulated properly. (That guide dates from 2019.)
Our view: that is why the foundation deserves its own decision on a new build. It is the one element you cannot economically improve later, and it decides how much heat is lost where the wall meets the floor.
What to ask when you are building new
If you are specifying foundations for a low-energy new build, these are the questions worth putting to any supplier:
- Which certificate covers my wall type, and does it cover the connection details I am using?
- What is the floor U-value for my perimeter-to-area ratio, with the slab thickness and insulation depth written out?
- What is the Psi-value at the wall-floor junction, and how was it calculated?
Our comparison of UK insulated foundation systems sets out what each supplier publishes, and What is the best foundation for a Passivhaus home? explains why the junction matters more than the foundation's name.
To be clear about scope: ISOQUICK is a new-build system. Its Kiwa BDA Agrément certificate covers insulated concrete raft foundations in new dwellings, so it is not a retrofit product. Our U-value tables show the floor figures for each build-up.
Where to learn more about retrofit
If the programme has you thinking about your own home, the Passivhaus Trust publishes retrofit resources for homeowners and professionals, including tips for affordable and staged retrofit, case studies and a masterclass webinar series. Its news item on the programme links to them.
Sources
- Passivhaus Trust — Guy Martin's 'House Without Bills' (10 February 2026)
- Homebuilding — World's first Passivhaus church conversion features in Guy Martin's 'House Without Bills' TV show (9 February 2026)
- Guy Martin Official — House Without Bills – update (10 February 2026)
- Passive House Plus — The PH+ guide to insulating foundations (June 2019)
This article is commentary based on the sources listed above.
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