The affordable Code 6 house has arrived
The elements of the natural-ventilation system of the ruralZED house (roof cowl with passive heat exchanger, inlet and exhaust ducts, and grilles) are all visible in this picture.
Delivering to Code 6 of the Code for Sustainable Homes requires a fundamental and joined-up rethink of how homes are designed and built. One example was in evidence at the recent EcoBuild exhibition. With Level 6 of the Code for Sustainable Homes, zero carbon, being the standard to be achieved by 2016, leading lights in the industry have been addressing the issue of how to achieve this requirement in an affordable manner. An impressive example of how the code can be met was very prominent at the recent EcoBuild exhibition at Earls Court in London with what was promoted as ‘the UK’s first affordable and commercial viable Code 6 house’. The full-size anatomical construction at EcoBuild was erected in just 3? days using quality materials that are designed to give such a house a life of five generations. The ruralZED housing system has been awarded on-site Code 6 status — eight years ahead of the Government’s targets for carbon-neutral new-build homes. It has a durable laminated-timber frame and incorporates high levels of thermal mass to keep its occupants cooler in summer and warmer in winter, state-of-the-art energy-saving building fabric and enough building-integrated renewable-energy systems to achieve zero-carbon status. By using a frame and traditional materials, as opposed to plastic foam, the construction is durable and avoids problems with off-gassing and poor indoor air quality that can be inherent with other modern construction techniques. It also has none of the concerns with combustibility that have been encountered with plastic-foam construction. The ruralZED housing system is available from £1150/m2 and £1550/m2, based on the purchase of six units at Code 3 and Code 6 status, respectively. There is an upgrade path from Code 3 to Code 6. This price is said to make it the first-ever carbon-neutral house kit that is commercially viable to build and affordable to buy and live in. Bill Dunster, director of ZEDfactory, the architectural firm behind the project, explains the benefits of the ruralZED house to developers and end users. ‘The main goal with carbon-neutral housing is to reduce carbon emissions and the risk of climate change. Until now, proposals and prototypes of other house designs have lacked the commercial and financial viability to make them serious alternatives to traditional housing and building techniques. ‘The ruralZED house has overcome financial constraints due to the strength of the ruralZED consortium, which has created a house that is, in addition to being the most ecologically sound housing option to date, affordable to build and desirable to live in — making it the most serious contender in the race to beat the effects of residential carbon emissions.’ The ruralZED housing system shown at EcoBuild offers detached, semi-detached or terraced houses of up to six units. The timber frame can be adapted to three storeys, with the same details and timber sections used for two storeys and embraces environmentally friendly, energy conscious, sustainable work and leisure places and master planning for complete ZED communities. The thermal mass is provided by concrete planks supplied by consortium partner Charcon Specialist. These panels are a thermally massive alternative to domestic plasterboard and are made using a high-recycled aggregate content. The introduction of GGBS (ground granulated blastfurnace slag) to the PFA/cement mix reduces the quantity of white cement required, increasing the green credentials of the panels. Each house include about 40 concrete planks with an area of 0.5 m2, each weighing 61 kg.
The key to keeping the interior of the ruralZED house warmer in winter and cooler in summer is the incorporation of thermal mass.
Matthew Hoad, head of BDa ZEDfactory, says, ‘We could not have achieved Code 6 without the input of Charcon. Its involvement has been crucial to the overall process.’ The high level of thermal insulation, 0.1 W/m2 K, is achieved using 300 mm of Rockwool’s non-combustible Flexi Insulation. This is a stone-wool product with a natural spring to ensure a flush fit that eliminates air gaps, even with out-of-true walls. It also moulds round surface irregularities such as bolts and fastening, to maximise air tightness and thermal performance. With such a super-insulated house, ventilation accounts for half the heat loss in winter. To reduce that heat loss, a wind cowl on the roof includes a passive heat-recovery ventilator to transfer 70% of the energy between the exhaust and fresh-air airstreams. An electric fan is not used to avoid having to use electrical energy from the mains or solar PV panels on the roof. Solar thermal and centralised biomass boiler plant are used to meet the requirement for domestic hot water and the small amount of heating that is required in the winter, about 2 kW, in addition to what is provided by ‘lifestyle’. Heat-pump technology is considered a no-go for such housing because of the electricity it consumes to utilise renewable energy. Another example of the attention given to minimising electricity consumption is the use of an induction hob in the kitchen for cooking, which uses 30% less energy than a resistance hob. The ruralZED concept has been developed for the UK climate. Bill Dunster explains that the ‘cold’ solutions developed for Scandinavian countries are not applicable to the UK, which, in future years, will have a Mediterranean-style summer, with its associated requirement for keeping cool.