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A practical design for affordable eco homes

Chemical giant BASF is using its know-how to build a template for energy-efficient houses

Project BASF house
Location Nottingham
Project manager Nottingham University’s Creative Energy Homes
Cost £70,000 per house
Architect Derek Trowell

At first glance, there is little to indicate a small house in a hidden corner of Nottingham University’s campus could end up being a beacon for sustainable housing developers.

Its outward appearance is modern, if unassuming. But it is what lies beneath which could hold the key to house builders finding the Holy Grail of delivering the affordable sustainable and energy efficient homes Government wants, but which won’t cost them a fortune to build.

This house is part of the University’s Creative Energy Homes Project. And £70,000 per home is the final cost that Claire Farrar, project and market development manager for German construction chemical specialist BASF, believes will efficiently deliver homes that exceed Level 4 of the Governments Code for Sustainable Homes.

“What we want to be able to do is improve the energy efficiency of new build houses. BASF has lots of experience in making houses more energy efficient, particularly in its home market of Germany and we want to be able to bring that experience to the UK market,” says Mrs Farrar.

Mrs Farrar is using a notional 20-home development for the project house, which will show that a single house design could be built anywhere in the UK and exhibit the same levels of energy efficiency regardless of local climatic differences.

This means that, despite the fact the homes will be host to most of the latest green gadgets, two of the most widely recognised systems for producing energy are conspicuous only by their absence.

Wind turbines and photovoltaics have not found their way onto the completed house - even though if they were used, they would probably shift up the sustainability scale by a couple of notches.

Affordable houses

“We could use micro wind turbines on this site,” says Mrs Farrar, “because it is suitable for them but we don’t want to because it’s not the point of the project.

“We want to be able to prove that a house like this, built on any site, will perform at a certain level.
“By adding a wind turbine we could probably move this particular house up from a Level 4 to a Level 5 but turbine-produced power is not transferable across all sites.

“By using photovoltaics we probably could have hit Level 6, but they are just too expensive at the moment and would have pushed the overall build costs up.

“Our goal here is to be able to show that affordable houses that exceed Level 4 can be built,” adds Mrs Farrar.

Like many of the best ideas, the final design for the BASF House was inspired by beer. However, in this case, it was not by its consumption, but by its brewing process.

Local architect Derek Trowell shaped the home’s look by borrowing heavily from the design of oast houses - traditionally used to dry hops through the natural circulation of air - and uses its chimney-like shape to draw warm air through the building.

That unusual design has seen the project team use a variety of techniques to build the house’s envelope.

Featuring a double glazed curtain wall on the south side of the two-storey plus room-in-the-roof house, a ground-air heat exchanger system that criss-crosses the small site and the energy-efficient properties of the insulated concrete formwork system and structural insulated panel systems that have been used to build the walls and roof, there will be no need for supplementary heating in the final homes.

“Initially, we had wanted to use a single glazing system for the curtain walling so that we could fully tap the effects of solar gain,” says Mrs Farrar.

“But they are just not available at the right price,” she adds.

In the end, glazing partners Rehau developed a double glazing system with a low energy efficiency or ‘U’ value outer pane to ensure the house benefits from the heat of the sun while the inner skin boasts a high U value to stop cooler air affecting the temperature within.

Ground cooling

Ducts draw heat into the house from the ground-air heat exchanger, a 50 m myriad of pipes that uses the ambient 10 deg C temperature of the sub-soil to heat the property during the winter and cool it during the summer.

Thermally-controlled windows at the top of the house are rigged to open should the house get too warm and close as it cools.

Innovation flows throughout the house from the roof Đwhere steel specialist Corus is using a standing seam type roof with heat reflective pigments developed by BASF down to the ground floor.

Here, expanded polystyrene systems are being used on top of the foundation and flooring package developed by precast concrete specialist Roger Bullivant.

The BASF house’s development signals a new ‘sensible’ approach to the economics of building sustainable housing, which many will undoubtedly find refreshing.

The trick now is for developers to start erecting more of their own.

A highly-efficient insulation system

The first floor and gable ends of the house are being built using a structural insulated panel system manufactured by Cheshire-based specialist, SIP Building Systems.

It has worked alongside BASF’s polyurethane producing arm Elastogran, producing panels primarily for use in cold storage facilities, but branched out to produce timber-faced panels a few years ago.

“We only ever use polyurethane foam to fill our panels,” says SBS general manager John Allan. “In the past, there have been concerns about the adhesive between the foam and the panels breaking down, but the polyurethane system ensures the foam and facing panel stick together and act as one solid section.”

SBS produces blank panels as large as 6.5 x 1.2 m which can then be cut to size and shape to fit the requirements of the design. Any individual project requirements can then be tailored before the panels arrive onsite.

“Services are face fixed to the inside of the panel which forms a service void once the studs and plasterboard have been fixed,” says Mr Allan. “But the beauty of SIPS is that they are compatible with most other building methods.”

Revolutionary roof

The roof panels feature an extra layer of orientated strand board sheeting to help carry the loads from the steel roofing system. But the bulk of the panels are of a standard 150 mm thickness with 128 mm of polyurethane foam sandwiched between two 11 mm thick layers of OSB.

The steel standing seam roof system being used on the project features pigments in the paint finish that are designed to reflect sunlight away from the roof, helping to ensure the fully utilised room-in-the-roof does not overheat.

BASF has teamed with roofing specialist Corus Colors to produce the pigments for its Colorcoat Urban roofing system.

“It’s our first venture into the residential side of the market,” says Paul Britchford, project manager at Corus Colors. “Using the system we can expect to save as much as five tonnes of carbon dioxide on this roof alone.”

And it is easy to fix with a breather membrane placed over the top of the SIPS roof and the 25 mm upstand seam roof fixed directly to the panels.

Airtight and insulated

Thanks to the unusual oast house design, a mixture of wall, roof and flooring systems are being used
on the scheme. On the ground floor is an insulated concrete formwork system which utilises BASF’s Neopor expanded polystyrene.

The Neopor EPS contains graphite which helps to boost the thermal energy performance of the ICF system. Manufactured by Poole-based specialist Logix, it boosts performance by as much as 12 per cent compared with other insulated formwork systems.

“It means the developer can decide if they want the extra thermal efficiency or scale down the wall thickness by 12 per cent to get the same performance but with increased internal dimensions,” says Logix general manager Jonathon Barnett. “We recommend a minimum thickness of polystyrene – its principal job is to be there to hold the concrete after all.”

Even that concrete has not escaped the touch of the BASF chemists as admixture specialist Ian Ellis explains.

“We wanted to produce a low energy, low carbon dioxide concrete that could be produced at any ready-mixed concrete plant around the country, he says. “By using a super plasticiser we can reduce the water content and boost the air content.”

Developed alongside Bardon Concrete and produced in water soluble bags, the admixture is added at a ratio of 500g for each cubic metre of concrete either on site or at the ready-mixed batching plant.

So convinced is BASF that the use of insulated concrete formwork will take off that it has launched its admixture sachets specifically for the market. “The sachets can be thrown into a truck mixer either at the concrete plant, in which case it will be ready for use as soon as it arrives, or onsite. It only takes five minutes for it to disperse throughout the mix.”

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