Bowen Consultants Limited Chartered Quantity Surveyors

The building will integrate the aspirations of Disability Essex with rigorous sustainable design and construction practices, leading to a robust, practical, cost-effective, replicable and demonstrably sustainable solution.  The building itself will provide a valuable lesson in integrated, cost effective and resource-efficient sustainable design for low CO₂ emissions whilst at the same time also demonstrating a number of methods of meeting this challenge using a variety of construction materials and technologies.  This has 3 benefits:

1.      Minimising the carbon footprint of Disability Essex on the environment

2.      Providing an environmental demonstrator building in its own right

3.      Minimising the charity’s on-going fixed premises & related running costs

KEY DESIGN FEATURES

The Passivhaus standard has the benefit of reducing the total energy demand to less than 15 kWh/m²/yr compared to current building standards at 55 kWh/m²/yr, this is achieved via a number of mechanisms. The Centre for Disability Studies has been orientated and designed to maximise passive solar gain and natural light, to reduce heat loss through an airtight, highly insulated thermal mass with the addition of mechanical ventilation with heat recovery. The operational carbon impact of the building will be minimised by utilising energy and water efficient appliances and equipment, and a highly efficient gas condensing boiler for the extremely low space heating and hot water demand, this may be supplemented with solar thermal energy.

The ‘thermally heavyweight’ construction is based on dense concrete block (an alternative currently being considered are thinner lime-based calcium silicate blocks) with localised and minimised steel reinforcement, on a concrete raft foundation with DPM, expanded polystyrene insulation and reinforced concrete screed. The raft foundation design significantly reduces the volumes of concrete required for foundations and further measures to reduce the concrete volume, and cement content are being developed. There are two types of external wall constructions. One type is the dense block structure with lightweight timber frame external frame containing recycled cellulose insulation (old newsprint) – being timber clad in either

European Larch or Douglas Fir (local or home grown, FSC approved). The other type is the dense block structure externally insulated with a new expanded polystyrene (zero ozone depletion potential) product with enhanced insulation capabilities, resulting in a thinner wall construction. This wall type is directly rendered. Windows and doors will be high performance timber windows, the frames externally insulated to reduce heat loss from these critical areas. Mineral fibre is a potential alternative insulation material in some wall and roof areas. The green roof is carried by a timber deck (and waterproof membrane) supported by fully filled timber ‘I’ beam rafters. The deck will be planted with drought resistant sedum plants (choosing as many local varieties as possible). The internal floor will comprise, polished concrete slab, clay tiles, natural linoleum or natural grade rubber. Waterless urinals, low flush WC’s, low energy lighting, energy efficient appliances and equipment will be fitted throughout.

In reducing air leakage from the building the heating demand is reduced. The mechanical ventilation with heat recovery (MVHR) system will have a recovery rate of over 80%, this will require a minimal additional heat source as the overall heat loss from the building has been so reduced, this heat demand is most cost effectively and carbon efficiently met by a gas condensing boiler.

The Green Roof has improved thermal performance compared to a conventional roof; it also improves rainwater management by controlling the volume and rate of runoff from the roof. Temperature variations are reduced, natural air conditioning is provided in high temperatures and air quality is improved through the absorption of organic volatiles and the release of oxygen and water vapour, as well as trapping airborne dust. The sedum is planted on a fine fertile substrate, providing a low maintenance roof and a habitat for flora and fauna