Eco home sweet home

Ring ring...

‘Hello... is that Claire?’

‘Yes… sorry, let me just… sorry, let me just stop the… ’

It’s impossible to hear what Claire Farrer is trying to say due to a loud roaring noise in the background. Finally, there’s silence.

‘Sorry about that, I’ve got a TV crew coming. I’m just doing the hoovering.’

While many project managers would confess to getting personally involved with their work, few would feel the need to do the cleaning as well. But having overseen the construction of the first BASF eco house, Farrer has decided to move in to see just how well it performs.

‘Maybe I’m getting too involved, but this building has been my life for the past two years,’ she confesses, adding ‘I sound a bit weird don’t I?’

The BASF eco house is a collaborative project between the University of Nottingham and German chemicals manufacturer BASF. It’s one of six experimental homes being built at the university’s School of the Built Environment in a project named Creative Energy Homes. Each house is built using different construction techniques and energy-saving technologies to achieve low carbon footprints.

The sustainable properties of Farrer’s house are only half the story. It has also been built with a budget of £70,000, based on a 20-house development, and relies as much as possible on its passive solar design and high quality insulation materials to minimise energy loss.

‘With our house we set out to show how sustainable housing can also be built affordably,’ adds Farrer. ‘It was important to lower the construction costs without recourse to expensive renewable energy devices. To that end the house relies as far as possible on passive solar design and quality insulation materials to minimise energy loss.

Cutting build costs is a major challenge for sustainable housing, especially with the government planning to build 4.2m new homes before 2016. Trailblazer eco-home projects like those on display at the British Research Establishment’s (BRE) Innovation Park in Hertfordshire have wowed the industry with their low-to-zero carbon ratings, but their heavy reliance on high-end renewable technologies ultimately makes them an impractical solution for rolling out on a large-scale basis. The prototype zero-carbon Kingspan Lighthouse, for example, was around 40% more than a conventional design, with the photovoltaics alone costing £40,000.

As Farrer explains: ‘People are quick to dash out to buy the latest wind turbine when they haven’t even thought about insulating their building properly. Insulation’s the most important thing.’

Emulating the German ‘Passivhaus’ standard (see panel), the BASF house relies on a compact floor area (roughly 8.9m x 7m) and a passive solar design to ensure thermal efficiency. Elevated ceiling heights help retain the feeling of space and comfort of occupants.

The concept is quite simple: three elevations are highly insulated, incorporating the minimum number of openings compatible with acceptable daylight levels, while the southern elevation consists of a fully-glazed, two-layer sun space. The east and west elevations are flat, making the house suitable for terracing.

The sun space allows solar gain in summer, and in winter the house is pre-heated using air pumped in from below ground. The house can be cooled by using air from below ground plus enhanced natural ventilation. A biomass boiler provides additional heating.

Construction materials were carefully selected to limit fabric and infiltration losses. Notably, the walls achieve a U value of 0.15W/m2 ºC through the use of lightweight BASF Neopor insulating concrete formwork (ICF) on the ground floor and structural insulated panels (SIPs) above. The monolithic structure of the SIPs significantly reduces wall joints, cutting air leakage and cold bridges.

‘The ICF was really easy to work with – it fits together like Lego,’ says Farrar. ‘And it’s cheap: a square metre of built ICF costs about £72. It took the team just three days to install the ground floor. The SIPS were all pre-fabricated off site, which speeded things up and tolerances were very low as a result.’

However, some problems with closing bridges between the ICF panels and SIPs meant installing extra interior insulation on site.

Farrar is impressed by the performance of the SmartBoard material used on the internal walls. ‘By storing up or releasing heat based on the temperature inside, this modified plasterboard is an energy efficient alternative to air conditioning,’ she says.

Combining several other insulating materials, renders and cladding, the BASF house achieves a code level 4 for sustainability, meeting government’s provision for sustainable homes up to 2016, when code level 6 becomes mandatory for all new homes.

‘Code 6 relies heavily on renewable technologies to produce energy to power, heat and cool new build houses,’ says Dr Mark Gillott, project manager for Creative Energy Homes. ‘But our £70,000 budget severely limited reliance on these technologies.’ Solar thermal panels provide 81% of the hot water requirement during summer, supplemented by a biomass boiler running on rapeseed waste meal during the winter. A rainwater harvesting system pumps water to the toilets and washing machine, while the ground-air heat exchanger improves ventilation and heating/cooling.

‘We couldn’t find an affordable way of producing our own electricity on site, so we’re using electricity from the grid to power our low-energy LED lighting and household appliances,’ says Farrar. ‘Photovoltaics just aren’t cost effective yet and wind turbines are non-transferable.’

The house can be upgraded to reach code level 5 at a later date, however, and there’s room on the south-facing roof to add PV panels.

An eco-bling, zero-carbon lighthouse it may not be, but the BASF house shows how an airtight, thermal efficient building can be built at a low cost. ‘Ultimately I think we’ve shown that the average builder can go out and do this themselves, there’s nothing used on the house that you can’t just go out and buy,’ adds Farrar.

The project by no means ends here. After Farrar has lived in the house for four to five weeks, students from the university will move in for an entire year. ‘We can monitor energy consumption and general use during occupancy,’ says Gillott. ‘The project really starts now. We can predict energy consumption through simulation, but only after people go in can we see if it works. It will be interesting to see how a code level 1 user gets on living in this home.’

As for Farrar, it’s time to relax and put sustainable construction out of her head for a while: ‘I’m going to have a cup of tea and put my feet up – Grand Designs is on TV!’

A new take on an old theme

The BASF house is a modern example of the Passivhaus, first introduced in Germany in 1990, writes Mike Priaulx.

A testament to German efficiency, Passivhaus (passive houses) are buildings that require little energy for space heating. Significantly cutting heating energy consumption means a radical shift in approach to building design and construction.

A passive solar design usually exploits a compact shape to reduce surface area, with windows oriented towards the equator to maximise solar gain. Super insulation dramatically cuts heat transfer through the walls, roof and floor compared to conventional buildings.

Building envelopes are extremely airtight with every construction joint carefully sealed, while mechanical heat recovery ventilation systems are often fitted (but not on the BASF house, which relies on natural ventilation) to maintain air quality and help recover sufficient heat to dispense with central heating. Intrinsic heat from internal sources such as waste heat from lighting is also maximised in the design.

The first Passivhaus buildings were built in Darmstadt in 1990 and now more than 6,000 have been built in Europe. In the UK, the five most significant projects are:

1. Sue Roaf’s house – 1995 

The Oxford Brookes University professor’s six-bedroom family house in Oxford was the first in Britain to have a photovoltaic cell installed on the roof. Natural heating is provided by sunlight and aided by triple glazing, 250mm of roof insulation, and 150mm floor insulation. Fuel bills are reportedly less than £150 a year, with construction costs the same as those for a similar architect-designed detached house built using traditional methods.

2. Hockerton Housing Project – 1998 

Five earth-sheltered houses on a 25-acre site in the north Nottinghamshire countryside designed by eco-architects Brenda and Robert Vale. Earth piled against building walls increases external thermal mass, thereby reducing heat loss and maintaining a steady indoor air temperature. This technique has been around almost as long as humans have been building their own shelter.

3. INTEGER Millennium House – 1999 

The brainchild of architect Nicholas Thompson of Cole Thompson Associates and information technologist Alan Kell, this house is insulated to a high standard using recycled newsprint cellulose. A conservatory acts as a passive solar collector, while additional heating comes from extracted ground water.

Natural ‘stack effect’ ventilation through ducts from the kitchen and bathrooms is assisted by a small fan powered by photovoltaic roof panels and wind turbine electricity.

4. BedZED – 2002 

The UK’s largest carbon-neutral eco-community, the Beddington Zero Energy Development, was developed by the Peabody Trust in partnership with Bill Dunster Architects and environmental consultant BioRegional Development Group.

As well as strongly relying on on-site renewable energy sources, buildings are enclosed in a 300mm insulation jacket and constructed from thermally massive materials that store and release heat depending on the temperature inside.

5. St Matthews – 2005 

Developed by PRP ZedFactor, a joint venture between PRP Architects and Bill Dunster Architects, this keyworker flat scheme in Brixton had projected heating bills of just £75 a year when built.

All internal space heating comes from the sun and from household appliances, while an airtight building envelope and very high insulation ensures strong thermal protection and energy efficiency at little extra build cost.