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Zero carbon-ready retrofit faces down climate change with contribution to national grid

Header Image

Words:
Mark Siddall

LEAP achieved the North East’s first Passivhaus certification for its Durham retrofit with an EnerPHit Plus rating, selling on the surplus energy it generates

When Paul and Sonny Shepherd bought a barn with extant planning permission, they wanted to create a contemporary, cosy and comfortable home with optimised air quality and low energy demand, and which touched the earth lightly.

The one-and-a-half-storey, three-bedroom house was designed to afford a better quality of life than that offered by the existing consent, while recognising existing planning constraints – the stone barn sits in a valley at the edge of Lanchester, County Durham – a sensitive setting albeit a brownfield site. From early on, concerns about ecology and whole-life carbon were central to the project. It is not only the first certified Passivhaus retrofit in the North East (a standard known as EnerPHit), but is rated EnerPHit PLUS, which means it generates more energy than it needs to operate.

The smallholding created around the house also includes a wildflower meadow, beehives, a small wood of 110 trees and four Miyawaki forests, which grow much faster than neighbouring woodland, jump-starting the forest creation process and capturing more carbon more quickly.

The position of existing windows gave limited daylight to the interior, which is now supplemented by new rooflights.
The position of existing windows gave limited daylight to the interior, which is now supplemented by new rooflights. Credit: Mark Siddall, LEAP

How we did it

Measures taken to reduce energy demand include high levels of insulation, zero thermal bridging (as assessed using the Passivhaus methodology), airtightness, and MVHR. The air permeability achieved is 63 times better than the regulations for newbuilds require (0.16 m3.h-1.m@50pa). The Equivalent Leakage Area is equal to a 1p coin every 106 m2 of surface area.

Inclusion of a 10.75 kWp photovoltaic array raised the EPC rating to A and achieves ‘zero carbon’ status. In addition to providing energy for use in the home, it exports electricity to the national grid. A Tesla Powerwall battery is used to reduce the peak load on the national grid. Payback for the system will be achieved within the 30-year lifespan.

Existing materials and structure were retained and adapted wherever possible. Elsewhere, natural materials and products were specified, with carbon-sequestering options favoured wherever practical. For example, a range of structural solutions were considered, but it was determined that timber frame would provide the open, airy spaces to which the client aspired, while limiting the carbon footprint when compared to masonry. Analysis shows that the cellulose insulation and timber frame lock in about 40 tonnes of CO2e.

Conscious of industry analysis suggesting that a typical newbuild house is responsible for 10 tonnes of construction waste, our materials efficiency strategy limited waste to pre-existing hazardous materials, and a very small quantity of insulation. Other on-site construction waste was all but eliminated. In fact only two small van loads of materials left the site and that went to recycling.

Upfront carbon emissions associated with the manufacture of photovoltaic panels were reduced from an assumed 179.1 kg CO2e/m2 GIA to 20.7 kg CO2e/m2 GIA – a factor of 8.5 times – by careful selection of products. As it turns out they account for 15% of total emissions.

  • Interior view.
    Interior view. Credit: Mark Siddall, LEAP
  • Interior view.
    Interior view. Credit: Mark Siddall, LEAP
  • Interior view.
    Interior view. Credit: Mark Siddall, LEAP
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What we learned

Lessons learned from the project are being shared at International Passivhaus Open Days and at PassivhausSecrets.co.uk.

For both whole-life carbon and operational energy the barn conversion achieves a 30% reduction compared to the RIBA 2030 Climate Challenge, and a LETI ‘A’ rating for upfront and whole-life carbon.

Monitored at five-minute intervals over 12 months, the house exceeded 25°C for just 0.7% of the year despite a heatwave – comparing favourably to the prediction of 2% made by the Passivhaus Planning Package. Over the entire year the mean internal temperature was 20.2°C.

Post-occupancy monitoring also identified an important performance gap, arising from poor calculation procedures within the SAP model that mask reality and therefore support false projections – specifically, that net zero carbon can be achieved while the national grid itself has not achieved zero-emissions status.

What we found was that over one year the photovoltaic array displaced 1957 kgCO2e of emissions, while 1578.4 kWh was imported from the grid, which resulted in 517.4 kgCO2e of emissions. In fact 68% of the total CO2 emissions (351.6 kgCO2e) occurred during the period between 1 November and 31 March, the ‘winter gap’ when photovoltaics do not cover the energy demand of the house.

But with this low energy demand, the photovoltaic array generates sufficient income to cover the home’s energy bills; over a 12 month period the total bill for space heating, hot water and household electricity was just £524, during which time energy generation produced an income of £1107.

In a time of climate breakdown, this barn conversion not only shows how environmental damage can be minimised but offers a clear indication of how it can contribute to more restorative actions, while letting the human spirit soar.

Mark Siddall is director of architecture and research at LEAP and a certified Passivhaus designer

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