Carbon Emissions: 15 kg CO2/sqm/yr
RIBA Architecture Award
RIBA Sustainability Award
RIBA Manser Medal shortlist
Cobtun emerges seamlessly from the surrounding landscape. Approached along an unmade road, a curved encircling mud and straw (cob) wall appears to crumble away at its southern end, enclosing a series of south-facing terraces. Further down an entrance leads through the massive wall to the front door and circular top-lit hall. Beyond, the cob continues past the entrance, the house abutting its south face in horizontally boarded oak and glass.
Arriving in the house, a sequence of south-facing living and bedroom spaces open out in two wings to the south and west, flooded with sunlight and seasonally shaded by 2m of over-hanging vines. Morning sun in the study is reflected from an external pool. Accommodation is all on one wheelchair-accessible level.
The site in Worcester City Council’s Riverside Conservation Area falls gently down to the Severn. The client’s brief consisted of ten words: “Humour, mystery and fantasy, ecological, sustainable, independent, contextual, agricultural, invisible.” Deyan Sudjic described “its aesthetic qualities [as] like a seamless Richard Long wall piece” and commented “it’s as much an advertisement for the pleasure to be had in building … as a manifesto for sustainability.”
The materials chosen combine a refreshing modern aesthetic with environmental responsibility. The raw medieval texture of the earth wall is contrasted with twenty-first century materials. As the majority of earth is from the site itself, there is virtually no transport or manufacturing, so the “embodied energy” of the earth walling is almost zero.
Very high insulation levels are achieved with recycled cellulose insulation. Low environmental impact building materials include paints and varnishes, sustainably sourced timber, recycled newsprint insulation, pvc-free wiring, etc. Render, screeds and mortar use sieved site sand, avoiding imported material; doors use translucent composite honeycomb panels, linen canvas and leather handles.
Passive solar measures are not too complicated or liable to mis-use or technological failure. Energy conservation includes solar panels to provide much of the hot water supply and rainwater harvesting for washing machines, wcs, and gardening. The original design allowed space for photo-voltaic electric roof panels, and these have since been retrofitted. Medium thermal mass – in floors, chimney, cob walling and concrete worktops – allows the environmental advantages of timber construction elsewhere. Low energy lighting and energy-efficient appliances are installed, with intelligent controls and a high-efficiency under-floor heating system.