Retrofit right: Shepherds Barn delight

Shepherds Barn EnerPHit was certified in 2020. It has recently been re-certfied to meet EnerPHit Plus standard

Shepherds Barn is a retrofit barn conversion located nearby to Durham. The project is the North East’s first certified EnerPHit project and achieved an impressive airtightness result of 0.18 ACH @50Pa. A timber frame structure was built inside the original barn building, which made it easier for the project to achieve the requirements of the EnerPHit (Passivhaus retrofit) standard. The project has since been re-certified to EnerPHit Plus certification status in February 2022, after extra renewable energy capacity was added.

Architect and Passivhaus Designer Mark Siddall from PHT member LEAP: Low Energy Architectural Practice was approached by clients looking to retrofit an existing barn building in rural County Durham and aiming to achieve ‘net-zero’ carbon emissions. Mark tested out various retrofit strategies using the Passivhaus Planning Package (PHPP) and concluded that the Passivhaus EnerPHit Standard represented the most appropriate approach, using an innovative timber frame solution. The project recently won the North East Regional LABC Award 2021 for best conversion to create a single new home.

By reducing energy demand without compromising comfort or indoor air quality, the retrofit demonstrates what can be done to reduce the environmental impact when converting an existing building.

The Passivhaus EnerPHit Standard was adopted because it is the world’s leading quality assurance standard for low energy retrofits. It is more cost-effective to save energy than generate it The EnerPHit space heating demand target was pursued, as this was the most cost-effective means of satisfying the clients’ aspiration of achieving “net-zero” carbon emissions.

Architect and Passivhaus Designer, Mark Siddall, LEAP

Key Stats

Occupancy: 4
Complete & certified: 2020
Form factor: 3.35
TFA: 144 m²
Construction: Timber frame within an existing barn

Construction

Working within the constraints of the existing barn building, issues around planning, structural instability and moisture issues all had to be addressed.

External wall insulation was never going to be possible on the barn, due to local planning requirements. However, the building’s wide floor spans made it possible to accommodate a cellulose insulated timber frame structure inserted within the existing barn walls. Creating an internal structure helped overcome the usual challenges of continuity of insulation and airtightness when working on older heritage buildings, making it possible to achieve exemplary standards of airtightness.

Shepherds Barn EnerPHit, Image credit: Eden Insulation

Wall

Timber frame with cellulose and wood fibre insulation
U-value: 0.12 W/(m²K)

Floor

Concrete slab on insulation

U-value: 0.14 W/(m²K)

Roof

Timber frame with cellulose and wood fibre insulation

U-value: 0.12 W/(m²K)

To address moisture risks, cavities between the barn walls and timber frame structure are well ventilated and microporous additives have been added to the lime-based mortar where walls have been re-pointed or replaced. The clients themselves attended a Passivhaus Tradesperson training event, enabling them to undertake and manage the construction work themselves, alongside Mark.

One of the most helpful things was going on the 2-day Passivhaus tradesperson course. It reinforced all the Passivhaus principles, and it enabled us to understand better why the house was designed how it was. It highlighted the importance of making it airtight, not only the techniques to do it but how to do it. That was really useful in the challenges of project managing.

Owners, Paul and Sonny

Predicted and Measured Energy Performance

The owners, Paul and Sonny, have been in their EnerPHit home since April 2020. Post-occupancy monitoring of Shepherds Barn’s energy performance is currently being undertaken, but anecdotal evidence is looking very positive.

Airtightness (≤1.0ACH@50pascals)	0.18 ACH @ 50 pascals
Thermal Energy Demand (≤25kWh/m².yr)	24 kWh/m².yr
Thermal Energy Load	12 W/m²
Primary Energy demand (PE ≤120kWh/m2.yr)	75 kWh/m².yr

In February 2021 Shepherd's Barn took part in the first ‘Passivhaus Challenge’. Homeowners turn off their heating to find out how long they can comfortably live without heating. During the week Paul and Sonny thrived to the extent that they even extended the experience for an extra couple of days. Meanwhile, a nearby house that had not been retrofitted, which started the challenge at the same time, survived just 14 hours before switching on the heating!

Shepherds Barn EnerPHit, Image credit: Mark Siddall

We feel very comfortable in the house. It's very resilient. We have never used the radiator in our south facing bedroom. Very rarely have we used the heating all day.... Probably only about 5 days a year. For maybe 4 - 5 months a year the heating is set 1 hour in the morning and 4 hours in the evening. That's the 2 downstairs radiators. What's so good is the lack of draughts!

Owners, Paul and Sonny

Shepherds Barn EnerPHit, Image credit: Mark Siddall

Renewable energy and embodied carbon

The photovoltaic array was upgraded (from 7kWp) to 11 kWp during the summer of 2021 and provides energy for use in the home, exporting electricity to the national grid. This charges a Tesla Powerwall, which is used to reduce the peak load on the national grid. By reducing energy in-use and generating renewable energy the project achieves ‘Zero Carbon’ status, eliminating carbon emissions, according to SAP (the Standard Assessment Procedure).

Shepherds Barn EnerPHit, Image credit: Eden Insulation

In addition to energy efficiency and renewables, the impact of embodied carbon was considered during the design and construction process. This meant the existing materials and structure were retained and adapted wherever possible, new build elements used natural materials wherever practical and efforts were undertaken to avoid waste. The materials efficiency strategy limited waste to the removal of pre-existing hazardous materials and a very small quantity of insulation. To all intents and purposes, on-site construction waste was eliminated.

Upfront carbon and embodied carbon was demonstrated using the LETI Embodied Carbon Reporting Template

Embodied carbon and Whole Life Carbon were assessed using PHribbon. The project then was inputted into the LETI Embodied Carbon Reporting Template to demonstrate the upfront and embodied carbon of the project. See here for the project input and data input.

Key team

Client: Private home-owners

Architect: Mark Siddall, LEAP

Contractor: Client self-builders

Certifier: MEAD

We’re really, really happy. It just feels really comfortable. The air quality is fantastic. It’s very easy to live in. We know it uses very little energy, which is a big thing and what we really wanted. We’re completely self-sufficient – we’ve got zero energy costs and we’re actually exporting energy to the grid.

Owners, Paul and Sonny

NB: SHD: Space Heating Demand, DHW: Domestic Hot Water, EUI: Energy Use Intensity

For more information, inspiration, and EnerPHit case studies please check here. Delve into our Passivhaus Retrofit Masterclass lecture series where we are taking an in-depth dive into achieving Passivhaus in several construction types including solid wall, cavity wall, step-by-step, multi-residential and non-domestic. Incase you have missed any of the sessions so far, all Masterclass lectures are recorded for all delegates to catch-up on.