Shepherds Barn

Construction

Almost 70% of the original barn was structurally unsound, with the threat of falling, and required significant underpinning and reconstruction. External wall insulation was not possible due to local planning requirements. However, the building’s wide floor spans did accommodate a cellulose insulated timber frame structure inserted within the existing barn walls. Creating a new structure within the existing helped ease the continuity of insulation and airtightness when working on older heritage buildings. 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. 

A literal labour of love - The enthusiastic clients took on on much of the physical work themselves. This informed the construction technology and process.  “It took us exactly one year, working eight to ten hours a day, six days a week,” says Paul. The clients undertook Passivhaus Tradesperson training, enabling them to undertake and manage the construction work themselves, under the general supervision/advice from the architect. Simple detailing was developed to reduce on-site skills requirement.

An insulated raft foundation system was used to help reduce thermal bridging and thermal bridge free detailing was achieved in most instances. The project made use of a standard prefabricated timber frame system insulated with cellulose reducing exposure to health and safety risks, saving time by changing the critical path (allowed external stone walls to be rebuilt while fit-out was being undertaken). The timber frame was craned in and erected in just five days. Stick built timber frame was used where prefabrication was inappropriate. 

It looked like a medieval ruin! We had to put the building back to look like the original barn, as stipulated by the planners. A Passivhaus retrofit is harder than building from scratch as you must work with an irregularly shaped external shell. The timber frame was erected in just five days.”

Owners, Paul and Sonny

Overall U-values Wall: 0.12 W/m2K Timber frame with cellulose and wood fibre insulation
Floor: 0.14 W/m2K Concrete slab on insulation.
Roof: 0.12 W/m2K Timber frame with cellulose and wood fibre insulation

Embodied carbon

The impact of embodied carbon was considered during the design and construction process. Existing materials and structure were retained and adapted wherever possible, new build elements used natural materials where practical, and efforts were undertaken to avoid waste. To all intents and purposes on-site construction waste was all-but eliminated as the materials efficiency strategy limited waste to pre-existing hazardous materials, and a very small quantity of insulation. Materials efficiency strategies included:

• Off-site prefabrication allowed offcuts to be reduced/recycled
• On site, reclaim, reuse and repurpose was prioritised. e.g.where additional stone was required, it was recovered from the site
• To avoid over-ordering, materials were only bought after measuring-up. Then, only once all materials had been used,were additional materials ordered.
• Some spare materials have been stored for reuse or repurposing.

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.

Building performance

Energy performance

The owners have occupied their EnerPHit home since April 2020. Post-occupancy monitoring of Shepherds Barn’s energy performance is currently being undertaken.

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! 

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). 

The average annual running costs work out as (negative) - £583 per year. Savings included foregoing underfloor heating – not needed as the structure had an excellent airtightness level as well as being well insulated – and installing only three radiators in the entire building.

Ventilation & summer comfort

The house has been modelled in PHPP to only exceed 25C only 2% of the time. In practice, summer overheating has been measured as less than 2%. Strategies developed to prevent summer overheating include:

• 0.75m deep window reveals
• Design for daylight
• Openable windows
• Rooflight shading (west facing)
• Summer bypass on MVHR system

Lessons learned

• The clients benefited from undertaking the Passivhaus Tradesperson course to enable them to undertake the project.
• Working with novice builders informed the construction technology and the construction processes chosen.
• The project demonstrates that, with good attention to detail, extreme standards of airtightness can be achieved with relatively little effort.
• Tackling up-front carbon is difficult, even with timber-based products. PHribbon offers an easy way for designers to assess up-front carbon.
• There were lessons in the variability of embodied carbon of solar PV panels on the market. Assessment showed the up-front carbon emissions associated with the photovoltaic panels were reduced from 179.1 kg CO2e/m2GIA (63% of total emissions) to 20.7 kgCO2e/m2 GIA (15% of total emissions) by selecting alternative products,  reducing the carbon intensity of the photovoltaics by a factor of 8.5 times i.e. 88%.
• A ground source heat pump (GSHP) was included in the project because the client had already installed the groundworks before engaging with a Passivhaus Architect. However, it would have been more cost-effective to use an air source heat pump (ASHP).

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

Further information

Shepherd’s Barn EnerPHit

Passivhaus Secrets

Passivhaus Retrofit

Homebuilding & Renovating: How this couple transformed a derelict stone barn into a stunning Passivhaus — and no longer pay energy bills - 02 June 2023

RIBA: Shepherds Barn - 2022

Treehugger: Passivhaus Challenge Shows How Well Passive House Buildings Hold the Heat – 22 February 2021

Back to 2023 UK Passivhaus Awards

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