Passivhaus Affiliate

EnerPHit breathes new life into Old Byres flint barn

The Old Byres is an existing brick and flint wall barn in East Sussex, which has been retrofitted to EnerPHit standard, via the certified component approach. The adoption of the EnerPHit standard was driven by the client, who has aspired for a sustainable comfy home.

The Old Byres EnerPHit

The Old Byres: Image credit - Enhabit

I have always wanted to design and build my own house and have wanted this to be a low energy, comfortable building. Passivhaus was the best answer to achieve all this.

 Richard C, Client 


The original building had a very high form factor, and the building shape could not be significantly changed on this retrofit. Component certification enabled reaching the EnerPHit standard, while fully protecting the fabric against moisture damage, as the insulation had to be retrofitted internally to retain the external appearance of the building, connecting to its local & historic surrounding countryside. 

Old Byres EnerPHit Old Byres EnerPHit
Old Byres EnerPHit

Key Stats

TFA: 169.2m2

Form Factor: 5.54

Start date: March 2015

Occupied: January 2016

Certified: June 2017

We were faced with a very high form factor (above 5.5) when starting the project. However, changing the shape of the building (and form factor) wasn’t a possibility on this retrofit. Therefore, this directed us towards the “certified component” approach to reach EnerPHit certification. This was also supported by insulating internally, to retain the external appearance of existing walls. However, reaching typical Passivhaus U-values on the existing walls (to meet the space heating demand criteria) would have meant pushing their performance too far, which could have led to moisture issues. By using the certified component approach, a compromise was  reached between thermal performance and protecting the fabric, while achieving EnerPHit certification.

Marine Sanchez, Enhabit


The main barn, with the addition of new-build extensions, is built with a new timber frame structure finished with timber cladding. The timber frame for the new walls and roofs and the use of a simple reinforced slab design, with insulation below, made the main parts of the construction simple to insulate.

Walls (exisiting)

Retained brick/flint walls with 200mm new timber frame installed internally, with stone wool insulation in between timber studs) 0.27 W/m2.K

Walls (new)

200mm new timber frame with 200mm stone wool insulation in between timber studs and 120mm externally  0.15 W/m2.K

Roof (existing)

50mm stone wool installed in between existing rafters, with 150mm rigid insulation installed internally 0.13 W/m2.K

Roof (new)

200mm new timber rafters with 200mm stone wool insulation in between rafters and 105mm externally 0.14 W/m2.K


RC slab, with rigid insulation below slab 0.18 W/m2.K

Windows (uninstalled)

M Sora Optimo XLT certified triple glazed timber windows 0.67 W/m2.K

Doors (uninstalled)

GBS Ultra opaque timber door, with vacuum insulated panels 0.56 W/m2.K

Old Byres EnerPHit


There were no services on the site and the choice of fuel for heating was therefore a choice between electricity or oil.  Space heating is provided via underfloor heating, utilising an air source heap pump (ASHP) as the main source.

Predicited Thermal Energy Demand (≤15kWh/m2.yr)

52 kWh/m2.year

Predicted thermal energy load (≤10W/m2)

25 W/m2

Predicted primary energy demand (≤120kWh/m2.yr)

158 kWh/m2.year

Airtightness n50 ACH@50pascals (≤0.6ach@50pascals)

0.85 ach @ 50Pa

Certified PAUL Novus 300 MVHR was crucial to meet the ventilation requirements. The shading strategy is dictated by deep window reveals and overhangs, with the potential for external shutters to be installed as a future-proofing measure against rising temperatures.


Key Team

Client: Richard C.

Contractor: Langtorr

Passivhaus Consultants: Enhabit

MVHR Consultants: Green Building Store

Structural Engineer: Hockley & Dawson 

Certifier: Cocreate

Apart from PHT member Enhabit, who were acting as Passivhaus Consultants, this was the first EnerPHit for all the team involved including the client. But thanks to their retrofit expertise, Enhabit ensured the project could be completed, knowing simplicity of the building fabric was crucial to success. As that the client was project managing the build, and the site team was small, without prior low-energy building experience, Enhabit made sure the design was kept as simple and robust as possible; ensuring it would be easily buildable and would deliver as expected. Following these principles, the build occurred relatively smoothly thanks to the care and commitment of the site team, supported by the client and design team.


This was the first house I supervised and project managed. Coordination was sometimes challenging on site, between all the different trades involved and the different materials required on site. The help of Enhabit and a creative structural engineer were essential roles. 

 Richard C, Client 


The 170m2 detached barn was certified in June 2017, with energy consumption monitoring on-going. Check it out this November as part of the 2017 UK Passivhaus Open Days.


25th September 2017

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