Off Grid 2030: Competition to design a family home to meet the RIBA 2030 Climate Challenge
The two acre site for Greensand is a well-wooded plot in the Sussex Weald. The ground slopes down from north to south and is accessed from the road in the north-west corner.
We explored the idea of building from materials found abundantly on site: earth, rich in greensand clay, and wood. Rammed earth walls would provide a load-bearing structure for a simple pitched timber roof. Selected mature oak would be identified early to be cut and sawn into lengths, stored and air dried for 1.5 years, and used for the exposed rafters.
Alongside these super-low embodied carbon materials, a Fabric First strategy will adopt passive measures including Passivhaus levels of insulation and airtightness, high thermal mass and rainwater harvesting.
The active methodologies proposed would include a 10kW photovoltaic array with battery storage, a ground source heat pump for hot water and heating, heat recovery ventilation with ground pipes supplying fresh air and a small wind turbine.
Greensand is a single storey dwelling with a legible plan composed of two principal volumes: bedrooms in the north and open-plan living in the south. In between, a recessed block provides front and back entrances, circulation and services.
Breaking the mass down in this way means that each roof can span the 4.8m width with ease. The low monopitch section allows high-level, north-facing clerestory glazing with intake vents on the opposite side, encouraging natural ventilation in summer. A small mezzanine deck in each bedroom within the higher volume provides space that can be used for home working or sleep-overs.
The 400mm thick rammed earth walls are externally insulated with wood-fibre slabs protected by a ventilated untreated timber rainscreen. Floors are earthen using clay from the ground, on a heated limecrete slab on cork insulation and compacted recycled glass. Fabric U-values and triple glazing areas conform to LETI targets. Insulated timber shutters limit heat-loss during winter nights.
We envisage that many of the materials and machinery could be transported to site in two reconditioned 20’ shipping containers, placed on a prepared limecrete slab and converted – after completion of the house – to an outbuilding containing plant for the heat pump, buffer tank, PV inverters and battery storage units. The outbuilding also accommodates a workshop, bin store, bike storage and EV charging point.
Preliminary energy calculations indicate that the building is carbon positive by 1.28 tonnes CO2 per year with an energy demand of 20kWh/m2, well within the operational energy target for 2030.