Green Building Store is now 21°

Shepherds Barn EnerPHit Plus

Shepherds Barn is a retrofit barn conversion undertaken to the EnerPHit Plus (Passivhaus retrofit) standard and designed by Architect and Passivhaus Designer Mark Siddall from LEAP: Low Energy Architectural Practice. The project involved constructing a timber frame structure being inside the original barn building and achieved an impressive airtightness result of 0.18 ACH @50Pa.

21° supplied the triple glazed PERFORMANCE doors and windows and Lacuna fold-aside doors for the project, as well as designing, supplying and commissioning the MVHR (mechanical ventilation with heat recovery) system.

Watch the video documentary on the Shepherds Barn EnerPHit project here: Passivhaus Secrets


The project’s clients were looking to retrofit their existing barn building to achieve ‘net-zero’ carbon emissions. Mark tested out various retrofit strategies using the Passivhaus Planning Package (PHPP) and concluded that the innovative timber frame ‘box within a box’ approach was the best solution. The timber frame structure inside the original barn building helped the project to achieve the requirements of the EnerPHit standard, making dealing with the thermal bridging and airtightness issues easier.  The project has a Thermal Energy Demand of 24 kWh/m².yr, achieved an airtightness result of 0.18 ACH @ 50 pascals and is a certified EnerPHit Plus project.

U values
  • Wall U-value: 0.12 W/m2K
  • Floor U-value: 0.14 W/m2K
  • Roof U-value: 0.12 W/m2K
Renewable energy

Shepherds Barn has an 11 kWp photovoltaic array which provides energy for the home, as well as exporting electricity to the national grid. A Tesla Powerwall is used for battery storage to reduce the peak load on the national grid. The project achieves ‘Zero Carbon’ status according to SAP (the Standard Assessment Procedure).

Embodied carbon

The impact of embodied carbon was also carefully considered. Embodied carbon and Whole Life Carbon for the project were modelled using PHribbon and also inputted into the LETI Embodied Carbon Reporting Template. Existing materials and structure were retained and adapted as far as possible and new build elements used natural materials wherever practical. Strong efforts were also made to avoid waste on site.

Triple glazed windows & doors

21°’s PERFORMANCE triple glazed inward opening tilt and turn windows, fixed windows and entrance doors were selected for the project. 21° also supplied the Lacuna triple glazed outward opening fold aside doors. All the windows and doors were finished in a RAL 7012 Basalt grey timber finish.

I have specified 21°s windows and doors for numerous projects and find them to be good quality and competitively-priced, as well as offering exceptional airtightness, as our brilliant airtightness results at the Shepherds Barn project demonstrate. It is also great to work with the knowledgeable 21° team who offered excellent customer service for the project.

Mark Siddall

MVHR heat recovery ventilation

21° designed, supplied, and commissioned the MVHR system for the project. A Paul Novus 300 with frost protection MVHR unit was specified along with rigid spiral wound steel ducting system.

When it comes to MVHR systems for Passivhaus buildings, 21° really understand the nuances and offer great support. It’s their depth of understanding that makes working with them so incredibly effortless.

Mark Siddall

21° are our trusted partners for windows and MVHR systems. When we’re working on a project they are the first people we contact, due to the combination of good quality products, knowledgeable technical support and great service.

Mark Siddall

More information

Watch the extended video documentary on the Shepherds Barn EnerPHit project here: Passivhaus Secrets.

Project details


Mark Siddall LEAP

Structural Engineer

Alison Church, Jackson Church 



EnerPHit certified


EnerPHit Plus certification


Case study


Life changing homes