Homing in on zero-carbon

Two houses being built by affordable housing specialist Lovell at the University of Nottingham in partnership with Tarmac have the potential to transform approaches to zero-carbon housing. The semi-detached houses will demonstrate how the highest levels of the Code for Sustainable Homes can be achieved at low cost using traditional masonry products and techniques. In the third of our regular project reports, Lovell regional director Noel Adams outlines the challenges involved.

The approach of the Lovell/Tarmac project team in drawing up the specification for these two houses – one of which will be built to Code for Sustainable Homes (CfSH) Level 4 and one to Code Level 6 – was to incorporate elements of the code into a ‘standard’ house type. The two semi-detached houses are actually a hybrid of the Lovell Rockley and Berrington house styles, adapted to accommodate elements required by the CfSH.

It is generally accepted that the first step to meeting the higher levels of the CfSH is to improve both the fabric insulation and the air tightness of the structure. By including 100mm of partial fill insulation in the brick and block cavity walls of the Code 4 house and using a biomass boiler to provide heating and top up for the solar hot water for both houses.

Meeting Code Level 6 is a much tougher challenge and the use of renewables is inevitable. The external walls are being constructed from a single leaf of Tarmac aircrete blocks with external insulation and render finish. Along with the solar hot water system we have included photovoltaic panels (PV) on the roof to accommodate the electric demand from lighting, pumps and fans and all the domestic appliance load.

In the ground floors and foundations we have tried two products. Firstly, there is Tarmac Heatsave Plus which is a flooring system using precast concrete beams and polystyrene infill panels – this fitted in with our strategy of improved overall thermal insulation. Secondly, we are usingTarmac Low Carbon Concrete (LCC) which will reduce the carbon footprint of the foundation by around 50 per cent.

The need to maintain a traditional feel to the homes meant that we had to find solutions for problems that may not have arisen on other similar schemes. A number of homes designed to meet CfSH requirements feature ‘upside-down’ living (bedrooms on the ground floor and living rooms up above) which makes it easier to achieve the required daylight standards. Because we wanted the homes to have a conventional layout, we have had to work hard to bring in extra light via sun pipes and the large sun space on the Code Level 6 property to realise the benefits of passive solar design in the winter months and tackle overheating in the summer.

Now we are on site, it’s time to put theory into practice. Given our extensive experience and sustainable construction expertise, we’re confident that our site teams can meet a challenge which will fully test our ability to deliver high quality workmanship. There is, for instance, no margin for error in relation to air tightness which is an essential element of the design of process particularly for housing designed to Code Level 6.

Working closely with our suppliers and subcontractors, at an early stage, is proving essential. The design of the boiler flue is just one example where we met early on with a specialist designer to ensure that our proposed solution would require minimum maintenance in the future. Our supply chain partners share our commitment to delivering these ground-breaking homes – which will look little different to any of the houses we build around the UK but could play a major role in helping achieve the industry’s goal of affordable, zero-carbon housing.

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Fact 37

20% of embodied energy is absorbed by concrete over a building's lifetime.
Source: Whole Life Performance Research by the Concrete Centre