Larch Corner Passivhaus: a timber triumph
The Passivhaus standard shows us how to massively reduce carbon emissions by cutting a building's operational energy requirements to the bare minimum. The next step to take us towards a net-zero carbon future is to pay attention to a building’s embodied carbon - and this certified project is a showcase of one way to do this.
Larch Corner, a new build detached home in Warwickshire, is all timber from inside to out. Its structure is CLT, the insulation is wood fibre, and the cladding is larch, all sustainably sourced. The low carbon materials, together with its Passivhaus-certified levels of energy efficiency, and a 9.3kWh PV array, make this a true net zero home, and beautiful with it.
PHT member Mark Siddall, the project’s architect and Passivhaus Designer, has calculated that the choice of an all-timber construction method over more traditional masonry has resulted in a reduction in embodied carbon of 40%.
He made the initial analysis using Environmental Product Declarations (EPDs – independently verified documents that give transparent and comparable information about the life-cycle environmental impact of products), and also compared this result to one derived from data from the ICE database (the Inventory of Carbon and Energy), using the PHRibbon tool for PHPP developed by Tim Martel. The two results tallied closely, good evidence that both methods are robust.
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The Passivhaus Standard was adopted because you can be confident about the quality of the house you are investing in. Not just in terms of the design and construction but comfort, air quality, noise, energy bills and reduced carbon emissions.”
Mark Siddall, Architect, LEAP
PHT member Mac Eye Projects was the main contractor on the project, and although this is the first Passivhaus the firm has completed, they went in well-prepared. Andy Mackay has a Passivhaus Certified Tradesperson qualification under his belt, and with PHT member Alan Clarke contributing services design and further Passivhaus expertise, a successful outcome was assured.
The light-filled, blonde wood interior, sheltered under deep window reveals and deep eaves, should stay cool in summer and warm in winter with minimal heating. With its internally voluminous spaces and minimalist detailing, it exudes a simple, calming and uncluttered sense of space.
The house also shows that Passivhaus buildings don’t have to be constrained in shape. With a form factor of 3.9, this single-storey, many-cornered detached wooden wonder takes no shortcuts to achieving the right level of energy efficiency. But the excellent u-values of the building fabric combined with an extraordinary level of airtightness keep the heating demand to just 14 kWh/m².yr, comfortably below the 15kWh/m².yr required by the Passivhaus standard.
| Construction | |
| Wall: | 0.092 W/m²K |
| Roof: | 0.122 W/m²K |
| Floor: | 0.101 W/m²K |
| Form factor: | 3.9 |
| TFA: | 162.5m² |
| Energy performance | |
| Thermal energy demand: | 15 kWh/m².yr |
| Thermal energy load: | 8 W/m² |
| Primary energy renewable demand: | 26 kWh/(m²a) |
| Primary energy renewable generation: | 38 kWh/(m²a) |
The record-breaking airtightness result of 0.047ach@50pa is testament to the commitment of the team and their attention to detail. To accurately measure such a low level of air leakage, airtightness expert Paul Jennings of Aldas was compelled to recalibrate his fan, and ATTMA attended the test as an independent witness.
Larch Corner has been shortlisted for the Structural Timber Awards Custom / Self Build Project of the Year, as well as the Low Energy Project of the Year category. For the latter, it’s vying with two other Passivhaus projects – Kintyre and Callaughtons Ash. Good luck to all - the winners are due to be announced on 9 October.
Learn more
Don't miss a rare opportunity to experience this scheme for yourself. Visit Larch Corner on the weekend of 9-10 November, when it will open its doors for the international Passivhaus Open Days.
Learn more about getting to net zero by reducing both in-use and embodied carbon at the Trust's forthcoming MASTERCLASS: Getting to net zero on 28 October in Manchester – and stay on the next day for Climate Emergency: Mainstreaming Passivhaus by 2030, this year’s UK Passivhaus Conference, at the same venue.
Further information
Treehugger: Larch Corner is a Passivhaus wooden wonder that shows how we should be thinking about carbon - 20 June 2019
MASTERCLASS: Getting to Net Zero
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