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LETI: 33,000 NET ZERO CARBON HOMES PLANNED
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lans for over 33,000 net zero carbon new homes are underway across the UK, Passive House Plus can reveal. Data collated by the London Energy Transformation Initiative (LETI) indicates that 33,000 homes at master planning level are set to be designed to meet key performance indicators for scalable net zero, as defined by LETI – meaning they are highly energy efficient, such that they are using their fair share of the UK’s predicted renewable energy supply. LETI told Passive House Plus a further estimated 2,500 homes currently at stage two to four (post
planning but pre construction) are also set to meet the key performance indicators. The LETI net zero carbon definition includes a total energy use intensity figure for energy consumed at the meter. The figure varies based on building type, ranging from 35 kWh/m2/ yr of gross internal area for dwellings, to 55 and 65 kWh/m2/yr for commercial offices and schools, respectively. LETI describe this as the maximum energy budget for the building, to enable a decarbonised grid to meet the remaining demand. The net zero carbon target also includes a space heating demand of 15 kWh/m2/yr. “It’s essentially building to the passive house standard with a heat pump,” said LETI’s Clara Bagenal George, adding that LETI’s targets were for in use energy, rather than just for calculated energy use. LETI’s rise has been little short of meteoric. While this may seem a remarkable phenomenon given the organisation’s voluntary, decentralised nature, Bagenal George cites these very characteristics as being essential to its success. “It wouldn’t have worked if it was a top down approach,” she said. “Our collaborative approach has fostered much more of a sense of ownership of the targets across the network.” The group was set up to work collaboratively to put together evidence-based recommenda-
tions for two pieces of policy – the new London Environment Strategy and the rewrite of the London Plan. In the absence of clear, credible statutory targets for net zero carbon buildings, LETI decided to set its own, preparing a one page definition of net zero carbon in December 2019, and the LETI Climate Emergency Design Guide in January 2020. “We thought we needed to define good,” said Bagenal George. “We’ve been astounded by the response. I think it shows the collaborative approach works, rather than just a centralised approach.” LETI subsequently played a key role in mobilising engagement in the consultation process for the Future Homes standard. Bagenal George said LETI began the process of collating numbers on projects so that other built environment professionals can point to the explosion of construction projects being designed to LETI’s net zero carbon targets. • (above) A rendering of a 600 unit net zero carbon passive house development planned for York City Council’s housing delivery programme. Designed by Mikhail Riches, who won the Stirling Prize for the Goldsmith Street passive certified social housing scheme in Norwich, the new scheme also features air source heat pumps and PV arrays, and may be an early example of the kinds of schemes built in accordance with the LETI’s net zero carbon performance indicators.
Poorly ventilated retrofits can double radon retrofit risk, study finds R
esidential retrofits must ensure ventilation is carefully considered in order to avoid an increase in radon gas levels, researchers at NUI Galway in Ireland have found. A team from the university’s school of physics conducted one of the first studies of its kind to quantify the impact of improved energy efficiency and airtightness on radon – a radioactive, odourless, colourless and tasteless gas that is a leading cause of lung cancer. The modelling showed that if appropriate ventilation measures were not considered during the retrofitting process, there is a potential for radon levels to more than double. However, the study also showed that when appropriate ventilation measures were implemented, radon concentrations could be reduced below initial levels. This finding is consistent with other evidence indicating that certain approaches may in fact reduce radon risks. As previously reported in Passive House Plus, a
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2020 monitoring study led by Barry McCarron found significantly lower radon levels in passive houses – which combine mechanical ventilation with heat recovery and advanced airtightness levels – than in neighbouring properties. The new study was carried out by Dr James McGrath and led by Dr Miriam Byrne as part of research funded by Ireland’s Environmental Protection Agency. It has been published in the international journal Building and Environment. “The research findings highlight that radon, and indoor air quality overall, needs to be given due consideration as a key element of any proposed retrofitting works,” James McGrath said. Radon is responsible for about four per cent of lung cancer deaths in the UK each year. The study, ‘Factors influencing radon concentration during energy retrofitting in domestic buildings: A computational evaluation’, is available online at tinyurl.com/ NUIGradon. •
