The theory of earth sheltered buildings isn't new. But in practice there isn't a lot of data about how they really work. Architect Jerry Harrall is set to redress this balance with his own living experiment in earth sheltered buildings.
What's the best way to find out about how earth sheltered buildings work? Design one, construct it and live in it would be the most obvious answer. That's just what chartered architect Jerry Harrall has done. He has designed and built an earth sheltered office for his Lincolnshire-based practice Sustainable Ecological Architecture (SEARCH) and on the same site, an earth sheltered home which will be occupied by him and his family. The construction is also part of Harrall's research for his PhD.

"The aim of this research project is to assess to what extent it is possible to construct zero space heated earth sheltered buildings, and achieve acceptable comfort zones," says Harrall. Both buildings also use low embodied energy construction materials, and the aim is that they have minimum environmental impact.

"We believe that the office is the first earth sheltered architects' office, designed specifically around passive solar design techniques, with the benefit of academic research. The dwelling is the first in the UK for similar reasons," he adds. But perhaps the most unusual feature, and the centre of the research project, is that 88 temperature monitors are built into the superstructure of the buildings to provide unique thermal performance data.

Both buildings are constructed using similar techniques and materials, with different layouts reflecting their different uses and periods of occupation. Both buildings are single storey, orientated south using passive solar gains as the main heat source, and passive ventilation techniques for cooling. The theory of the earth sheltering (and the main subject of the monitoring) is that it will maintain a steady internal temperature for both buildings (around 20°C) without the need for additional mechanical heating or cooling.

Site layout
Harrall built the office first, in order to identify any teething problems with the materials or methods of construction before tackling the larger project of the dwelling. At the time of BSJ's visit in March, the office was completed, and occupied, while the dwelling was in the early stages of construction.

Both buildings occupy land that was a former brickworks on the outskirts of a small market town. The buildings are set back slightly from the main road, with hedging that helps reduce road noise.

The 54 m2 office building is oriented south-south-east. The south elevation is a curving convex shape, with full height glazing, including the main entrance door which is also fully glazed. The office plan is semi-circular in design and includes a reception area, a design studio with three cad workstations for architects, an office and staff kitchen and toilet areas. From front to back, the office is open plan to maximise natural daylighting. Harrall has included high level windows on the north side of this building in order to provide consistent daylighting for the studio area. These north lights, as well as the other windows, also provide in excess of 8000 mm2 background trickle ventilation.

The 180 m2 dwelling faces south west. It is effectively a straight block, bent at about 120° around a circular living room which divides four bedrooms from the kitchen, utility and larder areas. Like the office, the southerly elevations are highly glazed to encourage passive solar gains into the house. This part of the house faces away from the road, providing privacy and an acoustical buffer for the occupants. The main entrance to the dwelling is from the north side. This has been specially designed to aid the process of passive ventilation (see below for further details).

By using the industry standard of 24 mm low-E double glazed units, the pragmatic adaptation of earth sheltering for affordable housing remains a reality. With this brief Jeld-Wen developed their Hi-Profile combi window range specifically for this project which is now included in their 2002 catalogue.

Environmental cement
Harrall is aware of the environmental problems associated with the manufacture of cement and the Ready Mix Bureau encouragement of cement part-replacement concretes. One such low embodied energy concrete developed by Professor Stanley Wild and Dr Martin O'Farrell of the University of Glamorgan was utilised commercially for the first time in which 10% of the cement is replaced with ground brick dust supplied by Hanson and mixed by Tarmac. Quartzite aggregate provides the dominant floor finish following grinding and polishing of the concrete.

The design of the floor and walls play an important part in the way the buildings work. The buildings are designed so that no excavation is necessary, making them more environmentally friendly. The foundation is a 200 mm reinforced concrete slab. This sits on 150 mm of rolled brick batts, beneath 200 mm of carrstone hardcore. The brick batts are recycled brick waste from Hanson's Whittlesey depot. For extra insulation, there is 140 mm of extruded polystyrene between the hardcore and the slab.

Walls are 300mm thick with two leafs of 100 mm Hemelite concrete blocks and a 100 mm cavity with reinforced concrete. Average U-value for the walls is 0·01 W/m2K, and for the floor 0·1 W/m2K. Averages are used, as the earth covering is at different depths around the buildings sides.

Keeping warm and dry
A tanking membrane is applied to the outer surface of the roof, walls and floors. Extruded polystyrene boards on top of the tanking add extra insulation. The extruded polystyrene is used on the roof and walls and is 140 mm deep. After this the earth (which is 100% recycled compost) is placed on top to a minimum depth of 750 mm which is dressed with a woven nylon membrane and evergreen herbaceous shrubs are planted through the membrane.

One of Harrall's main aims for both buildings is that they require no active heating system for heating and create no net contribution of CO2. "There is a low grade electric underfloor heating system consisting of low grade cable. The cables are interwoven with the underfloor metal mesh. This takes longer to install – days rather than hours – but gives an amplification of the heating process, making it more efficient." Laying the underfloor heating cables beneath the mesh also has the practical purpose of protecting them when the concrete is poured in. However, Harrall points out that the heating system has only been used for five days prior to occupation of the office. It is there purely as back-up in extreme low temperatures but it is not anticipated that it will be needed again.

After that, the office (and the dwelling once complete) relies on solar gain for heating and on the earth covering to retain the heat, and maintain a stable internal temperature.

Harrall says: "Weather in the Lincolnshire marshes is very humid. But between 150 mm and 450 mm below ground, we have found that the temperature is relatively stable. The theory of earth sheltering is that we can use this characteristic to stabilise temperatures inside the property. Harrall suggests that the 22 temperature monitors built into the office building superstructure may make the building the UK's most temperature monitored office building. Delta-T Devices of Cambridge supplied the monitors and monitoring software with indefinite monitoring in mind.

Naturally, with solar gain playing so important a part in the heating of the dwelling, there is the issue of temperatures rising too high in summer months. The orientation and design of the buildings mean that passive cooling is the main cooling method. "The office, for example, has a south east orientation. The office is also open-plan. On the north elevation we have high windows for north light, but they can also be opened to encourage cross ventilation." Because one side of the building will remain cooler than the other, air movement will occur naturally due to differences in air pressure, even on a still day.

The house also uses passive cooling in a slightly different way, as it is not open-plan. "The roof of the house is cantilevered. Full height walls create a funnel up to the door of the house on the north side. The front door can be left open with the benefit of security gates. This induces air movement from the warm south side of the house towards the cooler north side," explains Harrall.

Harrall's project though is more than simply an experiment in passive cooling and earth sheltered temperature control. He is passionate about sustainable building. Building materials and methods have been selected for minimal environmental impact.

For example, there are no embedded services in the dwelling or office. There are no ceiling or wall lamps, only standard or table lamps. These have battery operated infra-red switches. Electric heaters supply hot water for the house and office as needed. Harrall aims to supplement those with the use of solar heating eventually.

Low energy high repeatability
"We have used low embodied energy construction methods. We've also reduced the number of trades on site by 50%, and subsequently reduced the variety of materials by a similar amount. The cost of designing and building this four bedroom earth sheltered dwelling is less than the cost of a conventional four bedroom house via the self-build method. It is predicted that the annual running costs will be around a quarter of those required for a 'normal' dwelling. Harrall's earth sheltered building project is certainly a live test of an alternative approach building. His determination will enable others to benefit from the research.

This demonstration of techniques has already attracted interest from local councils, and other earth sheltered projects are in the pipeline. In the meantime, it is interesting and encouraging to see at least one architect who is prepared to live with and in his own experiment.

Manufacturers and suppliers to the earth sheltered project, Long Sutton

Back up heating
De-Vi Electronics

Insulation
Springvale Combat

Facing bricks
Hanson Bricks

Tanking
Delta Membrane Systems

Earth cover
Organic Recycling

Joinery
Jeld-Wen UK

Concrete
Tarmac Topmix

Concrete blocks
Tarmac Topblock

Monitoring equipment
Delta-T Devices

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