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Janet Cotterell

MSc in Advanced Environmental and Energy Studies, Certified Passivhaus Designer, Co-author of The Passivhaus Handbook.


Janet practiced as an architect for many years, before focussing on developing a timber frame construction method directed at energy efficient new-build  homes, optimised for a heating demand performance from 15kWh/m².yr to 25kWh/m².yr. The PH15 system is based on a breathable timber frame shell, addresses typical thermal bridges and ensures ultra simplified air-tight details. PH15 projects have been granted permission in challenging settings - Green Belt, Conservation Areas, and a National Park. Janet is interested in multi-unit housing projects where the PH15 construction system offers greater cost certainty while also ensuring design intent is realised as-built.  Winner of the UK Passivhaus Awards 2013 for best private house.


Janet supports architects and clients who adopt the PH15 construction method, providing full technical back-up. PH15 addresses common concerns around cost and quality control especially when the brief is to deliver highly energy efficient homes, including zero energy homes. Janet delivers contractor training as an integral part of any PH15 project, including MVHR design and triple-glazing specification.


The PH15 System, finalist in Structural Timber Awards 2016 for ‘Most Innovative Product’. Best air-tight result 0.09 ach@50Pa.

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