The future of housebuilding in the UK is amongst us. Almost a full decade before zero-carbon homes are mandatory for private new properties, self-build specialist Potton, in conjunction with architect Sheppard Robson, has created a flagship prototype, the lighthouse, which reaches level 6 (the highest achievable) of the Code for Sustainable Homes.
Open to the public on select days at the Building Research Establishment (BRE), Watford, the Lighthouse prototype – of which retail models are for sale – is a two-bedroom unit built on three floors, one of which is a mezzanine level. Describing it thus though is akin to saying a car has four wheels and a body. It does but it has so much more than that too.
Aesthetically, the external 40-degree angled roof – on one side only – gives it the appearance of a ski slope. The building’s exterior is clad in sustainable sweet chestnut cladding, sourced from a farmed forest in Hampshire. Fast-growing it has a high resin content that naturally protects the timber from bleaching, negating the need for regular upkeep.
The distinctive house shape is topped off by a large, centrally located glass wind catcher, which provides passive cooling and ventilation, as well as allowing light to steam down through the stairwell. Structurally, the timber frame unit sits on screw piled foundations, raising it off the ground and reducing the high-embodied carbon footprint of traditional concrete slab foundations.
The building envelope utilises the Kingspan TEK wall system, which provides high thermal efficiency and air tightness. The μ-values are 0.11W/m2k compared to existing building regulations that only require a μ-value of 0.35W/m2k. Allied to triple glazed, gas filled windows, and south facing orientation (ideally) for maximum natural sunlight, cooling rather than heating the house is the main issue.
Potton estimates that space heating will only be required for a couple of months each winter. When it is required, mainly it will be provided by pv panels to supply electricity to power the house; solar power will generate the hot water required. In winter, when there is insufficient sunshine, an installed biomass (run on CO2 neutral wood pellets) boiler will supply the hot water and space heating requirements.
Excess electricity would be sold back to an energy provider – houses should be on the main grid as there is no battery backup provided as standard. Potton estimates, backed up by independent analysis, that the homes will be operationally net-zero carbon over the course of a year i.e the energy used would be less than that that sold back to the grid.
In total, the energy cost of running the house would be £31 per annum compared to £500 for a house of a similar size and shape built to 2006 building regulations. Embodied energy in the construction process is less than a conventional property too. Wood for Good estimate a saving of circa four tonnes of CO2 will be saved on a timber frame house with wooden windows versus a brick and block house.
Operational eco-initiatives include low water shower, dual flush toilets, grey water recycling for WC flushing – with an average saving of 50 per cent compared to a conventional house – and rainwater harvesting for use for a wash machine and irrigation. Smart metering records energy consumption, allowing the occupants to monitor and adjust their behaviour accordingly.
If all this sounds so worthy, you might imagine you are being asked to live in a horse-hair house, the truth couldn’t be more different. Internally, the house is light and airy. Pale coloured wood (sustainably managed), glass and steel are featured throughout. Recycled rubber flooring to the ground floor is a vibrant green colour; white walls and ceiling height windows give privacy and natural daylight.
In the prototype, the two-bedrooms and bathroom are located on the ground floor. Open plan stairs lead up to the double height sitting room with mezzanine floor reached via a second staircase located in the middle of the house. Way above that still is the innovative mechanical ventilation and heat recovery system that provides passive cooling throughout the house.
The ambience is chapel like, meditative and serene. One can imagine living happily and soundly in this space.
So, what chance we all can? Well, large housebuilders are interested to know how the company has achieved Code Level 6. Joe Martoccia, sales & marketing manager for Potton, says: “We are working with Barratt in an advisory capacity. They are keen to hear and see what we are doing, but the cost of building a house like the lighthouse on a large scale is an issue for them at present.”
A 92.9m2 two-bedroom unit like the lighthouse prototype, reaching Code Level 6 costs from around £185,000 (£1,990 per m2) depending on the exact specs included (exc. land). At Code level 6 all the energy is from renewable sources, which would include heat recovery to add to the ventilation unit, solar thermal hot water and biomass boiler and total renewable energy such as solar and photovoltaic (pv).
A lighthouse built to Code level 4, which would include triple-glazed high performance windows and mechanical ventilation, would cost around £1,450 per m2. A Code level 5 house, including some renewable energy technology, would be priced at a level between the two. A conventional Potton home, which meets all current building regulation requirements that are set just below Code level 1, is priced from £970 per m2.
As yet no grants are available for the purchase or install of renewables in the lighthouse in England, notes Potton, although in Scotland some concessions are said to be available. A one off stamp duty exemption is granted, however, for all net-zero carbon homes for sale priced up to £500,000. Where the house price is greater than half a million, a reduced one-off stamp duty charge of £15,000 is charged.
Potton is creating a range of lighthouse designs for launch in mid-2008. House specifications will be made available in different sizes (including three- and four-bedroom models) and shapes, as well as to Code levels 4, 5 and 6. Within a loose framework provided by the lighthouse design, Potton will work with prospective self-builders to incorporate bespoke features and smaller/larger footprints as required.
Manufactured off-site and installed by crane on-site, build time is generally less than a week. Potton claims from order to completion can be achieved in eight-ten weeks, assuming planning and utilities and infrastructure are in place. Planners are said to be supportive of the lighthouse design. To date, three around the country, in different regions, are being built and none has run into consent problems.
Regarding upkeep, Potton says post-sales maintenance contracts will be set up with third parties or directly with the manufacture where the products are not Potton supplied. For example the pv panels will require monthly cleaning to remain at their most efficient, which is a job only experienced and knowledgeable contractors should undertake lest they get damaged.
This article began by saying the lighthouse was the future of housebuilding – but for all or just a lucky few? Presently, you’d have to say the latter. But, importantly, Potton is demonstrating that the technology and skills exists to build net-zero carbon, stylish and contemporary houses in the UK. The question now is can it be achieved in a cost-effective manner for everyone’s benefit. For all our futures, let’s hope so.
