Stretford Passivhaus retrofit TV makeover

The deep retrofit of a modest Manchester semi-detached home to the Passivhaus retrofit (EnerPHit) standard will feature in the Channel 4 programme Guy Martin's 'House without bills', which will air on Monday 9 February 2026. The Stretford Passivhaus retrofit project uses a wide range of retrofit strategies, which include useful replicable technical lessons.

Stretford Passivhaus retrofit. Image credit: North One/ Channel 4

The house is a very typical 1930s semi-detached house and has been radically transformed, reducing its heating demand by approximately 90%. Retrofit measures include internal wall insulation to the front elevation, external wall insulation to the rear, the addition of a single storey extension, a newly insulated ground floor, upgraded loft insulation and high-performance triple glazing throughout. Airtightness was prioritised, with the project exceeding expectations by achieving an impressive 0.93 ACH @ 50Pa, representing roughly a 90–95% improvement on the original building.

Guy Martin's 'House without bills'. Image credit: North One/ Channel 4

Timber cladding, white bricks and a striking metal roof create a contemporary feel to the otherwise understated home. A vaulted ceiling with exposed oak rafters and a triple glazed rooflight, create a dramatic, bright space. The home has been reconfigured to provide flexibility, with the potential for ground floor living.

PHT member Progress in Practice is Architect and Passivhaus Designer on the project, working closely with PHT member Myzsa Group acting as main contractor. The project will be certified by PHT Member ZE Passivhaus. Hannah Dixon from Progress in Practice and Joshua Day from Myzsa Group appear on the programme alongside Guy Martin.

Key stats

Construction: Retrofit hybrid EWI & IWI insulation, and timber I-joist extension.
TFA: 105 m²
Build start date: March 2025
Completed: 2026
Certified: Targeting EnerPHit

Stretford EnerPHit. Imge credit: Progress in Practice & Alex Dormon Photography

Guy Martin and Andy Burnham at Stretford Passivhaus retrofit. Image credit: North One/ Channel 4

The clients wanted to create a comfortable, flexible and healthy ‘forever home’, and a deep whole house retrofit was the best way to achieve this. After Progress in Practice undertook initial PHPP modelling on the home, and it became clear that the EnerPHit standard was feasible for the project, the clients decided to go all in for EnerPHit.

The retrofit has incorporated futureproof designs to create a comfortable, accessible and healthy home that will support the owners throughout their retirement. The result is a home that allows them to live in long-term comfort, without concern over rising energy costs or reduced mobility forcing a change in living circumstances.The addition of a modest rear extension offers future flexibility should it ever be required and an accessible ground-floor shower room supports single-level living.

Delivering this EnerPHit retrofit was technically demanding but very rewarding. Working within the limits of an existing building meant careful detailing throughout, close coordination with the design team, and a consistent focus on build quality on site. Meeting EnerPHit standards encouraged us to sharpen our approach to airtightness, insulation continuity, and sequencing, as well as navigate the challenges of material selection and available local trades. The finished result speaks for itself — a comfortable, low-energy home that performs exactly as intended. Having the construction process documented also reinforced just how important it is to get the fundamentals right at every stage.

Joshua Day, Managing Director, Myzsa Group

Construction

Single story extension at Stretford EnerPHit. Image credit: Progress in Practice

Airtightness grommets at Stretford EnerPHit. Image credit: Progress in Practice

Stretford EnerPHit under construction. Image credit: Myzsa Group

Extension groundfloor at Stretford Passivhaus retrofit. Image credit: Myzsa Group

The 1930s semi-detached brick cavity wall house required different insulation strategies, depending on the elevation or whether the element was part of the existing building or extension:

Floor: The suspended timber floor was removed and replaced with a solid concrete slab insulated with PIR insulation.

Walls: Brick cavity walls were filled with EPS beads. In addition:

Front elevation walls were insulated internally, with lime plaster and wood fibre internal wall insulation.
Rear elevation walls were insulated externally, with with mineral wool external wall insulation.

Roof: The existing clay roof tiles remained in place. The house has a cold roof, which was topped up with mineral wool insulation at loft level.

Extension: The extension was built using timber I joist with cellulose insulation, with timber cladding and render to the party wall. The extension roof involved a timber deck and PIR insulation above, finished with standing seam steel roof.

Embodied carbon

A number of measures contribute to reducing the embodied carbon of the project. Internally, natural materials such as engineered cork flooring, exposed oak rafters and timber window reveals are used. Plant-based materials, lime plaster and mineral paints enhance internal air quality by minimising VOC emissions. Externally, timber cladding is specified, while the rear extension was constructed using an engineered timber frame with recycled newspaper insulation. The front of the house was insulated internally with wood fibre and finished in lime plaster.

Sustainability was also embedded through reuse: the owners sourced a second-hand kitchen with high-end appliances, reused existing paving slabs, and incorporated reclaimed 1930s internal doors.

U-values

Roof:

Extension: 0.14 W/m²K

Existing: 0.11 W/m²K

Wall:

Extension: 0.11 W/m²K

Existing (EWI): 0.16 W/m²K

Existing (IWI) 0.24 W/m²K

Floor:

0.14 W/m²K

Building performance

Airtightness n₅₀ (≤ 1.0 ACH @ 50 Pa)

0.93 ACH @ 50 Pa

Space Heating Demand (≤ 25 kWh/m².a)

25 kWh/m².a

Heating Load

17 W/m²

Primary Energy Demand: (≤ 120 kWh/m2.a

70 kWh/m².a

Primary Energy Renewable (PER) Demand (≤ 60 kWh/m².a*)

57 kWh/m².a

*+/-15 kWh/m².a allowance if offset by energy generation. See Passivhaus criteria.

Services

Heating strategy: An air source heat pump provides the heating and hot water and the home's original gas supply has been entirely disconnected. By retrofitting the home to the EnerPHit standard, the energy required to heat the home has been minimised. As a result, it has been possible to install a very small air source heat pump to meet the remaining demand. Because the heating requirement is so low, the system is inexpensive to run, and this is reduced further through the addition of solar panels and battery storage, helping to future-proof the home against rising energy costs.

Renewables: A small PV array with battery storage contributes to the energy for the home.

Ventilation strategy: A balanced MVHR (mechanical ventilation with heat recovery) system supplies filtered fresh air without compromising thermal performance. This not only improves air quality but also reduces the risk of moisture and mould while extracting internal pollutants.

Summer comfort: PHPP modelling demonstrated that overheating risk for the project was low, partly due to existing overhangs on the front (south) elevation.

Guy Martin at Stretford Passivhaus retrofit. Image credit: North One/ Channel 4

Challenges & lessons learned

Existing building challenges: With any retrofit the main challenges tend to come from the existing building and the hidden secrets it holds beneath the plaster. In this case, the team found that the front bay was constructed from brick supported only by a hollow PVC window frame, the wall ties had corroded in the flank wall and 1930s concrete blockwork was found which "you could poke your finger through".
Airtightness strategy: The airtightness strategy for the project was very robust and is likely to be replicated in future projects. .
Project team The project team worked well together. The team included a mix of Passivhaus experienced practitioners and those new to Passivhaus, which worked well, advancing training while also ensuring knowledge levels across the team were high.

Architect’s view

What the Passivhaus standard does for us, is it provides a target, where we can say to our clients with confidence that this will create a genuinely comfortable home with minimal fuel bills. There's no vagueness to it; no estimating or guessing. It has already been tried and tested to work. So follow the methodology and this is how you get a high quality home or building.

The Stretford Passivhaus Retrofit demonstrates how an ordinary house can be transformed into something quietly extraordinary. By combining deep energy retrofit principles with thoughtful spatial design, natural materials and long-term adaptability, the project shows that sustainability and comfort are not opposing goals, but mutually reinforcing ones. It is a home designed not just to perform exceptionally today, but to support dignity, wellbeing and independence well into the future—proving that truly sustainable architecture is as much about people as it is about energy.

Hannah Dixon. Director, Progress in Practice