'All shook up': The Elvis House EnerPHit

A derelict council house in Canterbury has been brought up to EnerPHit (Passivhaus retrofit) levels of performance. Heating demand has been reduced by over 91%, through whole house retrofit measures and installation of a heat pump.

The retrofit of 31a St Peters Place in Canterbury (also known as the Elvis EnerPHit, thanks to its previous owners' prominent poster display of the musical legend) was commissioned by Canterbury City Council. Prior to the retrofit, the house would have needed nearly 25,000 kWh of heat each year to stay warm. Now it needs just 2,216 kWh — an incredible 91% reduction. With an efficient heat pump added, this drops to just 815 kWh/a with the predicted COP of 3.4 - a 97% reduction. In terms of total energy use, the entire home is predicted to use just 2,820 kWh of energy per year, which is less than many small flats and far below typical UK homes.

Designed by PHT Patron Eco Design Consultants, with M&E Design by PHT Patron 21 Degrees, the project was built by PHT members Serenity Projects SE Ltd, and certified by PHT members ZE Passivhaus.

Key stats

Construction: masonry construction with external wall insulation.
TFA: 68.5 m²
Build start date: 2025
Completed: 2026
Certified: EnerPHit, 2026

Elvis EnerPHit Canterbury under construction. Image credit: Eco Design Consultants

The transformation at 31a St Peters Place is a shining example of what a high‑quality whole‑house retrofit can achieve.

This home now delivers outstanding comfort, air quality, and energy efficiency all year round. The retrofit dramatically improves insulation and airtightness, meaning the home stays warm with remarkably little energy. Even on freezing winter days, every internal surface stays at a comfortable temperature — eliminating cold spots, draughts and the risk of condensation and mould.

Canterbury City Council

Elvis EnerPHit Canterbury. Image credit: Eco Design Consultants

Construction

The 1970s masonry-built council home was retrofitted with fire‑safe external wall insulation, with a warm loft and insulated floors. The Passivhaus retrofit achieved the EnerPHit standard, via the Component route.

Thermal bridges are greatly reduced so that surface temperatures of all walls, windows are at a temperature of above 17deg C even if -5 deg C outside, making the new home comfortable, removing risks of condensation and mould. As an airtightness measure, the soil vent pipe was replaced with air admittance valve and manhole vented.

U-values

Roof: 0.137 W/m²K

Warm loft, with 120mm RIR over the roof trusses and 100mm mineral fibre between.

Wall: 0.140W/m²K

250mm of fireproof mineral fibre external wall insulation.

Floor: 0.107 W/m²K

Floor insulated with 200mm PIR insulation.

Building performance

Airtightness n₅₀ (≤ 1.0 ACH @ 50 Pa)

0.8 ACH @ 50 Pa

Space Heating Demand (EnerPHit Component method)

32 kWh/m².a

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

57 kWh/m².a

Overheating %

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

Services

Heating strategy: Heating and hot water are provided by an ASHP (Air Source Heat Pump) with a predicted COP (Coefficient of Performance) of 3.4.

Ventilation strategy: A mechanical ventilation with heat recovery (MVHR) system supplies fresh, filtered air throughout the day. It captures over 90% of heat that would normally be lost through ventilation, keeping the home warm while ensuring the air stays clean and healthy.

Renewable energy: With 8 solar PV panels producing around 2,584 kWh a year, the home now generates enough electricity to cover all its annual heating requirements, and around 92% of its total energy use.

Summer comfort: The project has been carefully modelled with summer comfort in mind. Overheating risk is now effectively eliminated and is expected to exceed 25°C for less than 0.1% of the year.

Challenges & lessons learned

Importance of early design stage: From the outset it allowed for realistic targets to be set and communicated to all team members.

Airtightness: The airtightness was particularly difficult to achieve as the airtightness membrane needed to be placed over the original rafters, with insulation on the outside. Initial air pressure tests did not achieve the required 1.0 ach @ 50 Pa and was assumed that some small holes had been made through the membrane which were undetectable. Using the AeroBarrier system enabled the project team to meet EnerPHit airtightness levels, achieving an airtightness of 0.8 ach @ 50 Pa.

Architect’s view

“As the architect on this project I believe that ultimately EnerPHit certification reduces risks and gives certainty on performance, giving real value. As architects this gives us confidence and a second pair of eyes that what we design is realised, and our clients achieve the comfort and wellbeing they deserve.

The results speak for themselves: lower bills; a healthier indoor environment; ultra‑stable temperatures; drastically reduced carbon emissions; a more resilient home ready for future energy challenges.

31a St Peters Place is now not just a home — but a model for how older buildings can be transformed into modern, low‑energy, high‑comfort living spaces.”

Alan Budden, Director, Eco Design Consultants

Key team

Architect & Passivhaus Designer: Eco Design Consultants
Contractor: Serenity Projects SE Ltd
Structural engineer: EPS Design
M&E consultant: 21 Degrees
Passivhaus Certifier: ZE Passivhaus

Elvis EnerPHit Canterbury. Image credit: Eco Design Consultants

We applaud Canterbury City Council for adopting the EnerPHit standard for the Elvis House project - an exemplar that can inform other housing stock in the city and region. As demand for high-performance buildings grows, the question is no longer whether we can deliver them, but whether we are prepared to do so at the scale required.