The Characteristics of an Earth Sheltered Dwelling

a. Earth-Sheltering

This provides a layer of natural insulation but also helps make the buildings visually unobtrusive and preserves the land surface for wildlife use – earth-sheltered buildings blend into the countryside.

b. Super-Insulation

High levels of insulation retain the heat gained by the use of premium performance rigid insulation with elemental u-values that are far better than the minimum building regulation requirements. By minimising thermal bridging, it makes it possible to reduce the rate of heat loss from the building while increasing its capacity for retaining stored heat.

c. Thermal Mass

The thermal mass (the structure) is placed inside the insulation to provide a heat ‘battery’ to hold onto the heat gained. The internally exposed elements work to stabilise the internal ambient air temperature by acting as heat-sinks.   This will warm the house in cold periods and also cool the house in very hot periods.   The overall affect is to maintain a constant year-round internal temperature within a narrow band of fluctuation. There is a video explaining how this combination of insulation and thermal mass works on the Hockerton Housing Project website  ‘Heat Battery Thermal Store at Hockerton HP’.

d. Biodiverse

Earth-sheltered buildings maximise the landscape available to nature. Apart from small recreational lawn areas in front of the dwellings and the roads the rest of the site will be left to full natural development.  This will result in a rich variety of trees, shrubs, bushes and grasses that provide a large area for biodiversity on the site.

e. Orientation and Glazing

By maximising the areas of high specification glazing on the south elevation of the building the opportunity for solar gains and high levels of daylight into the home are optimised. By reducing the glazing areas on the north, east and west elevations, the rate of heat loss from those sides of the building most prone to higher rates of heat loss is minimised.

f. Courtyard Micro-Climate

A bunded courtyard induces a micro-climate that retains warmth to the front of the buildings

g. Ventilation

The layout of the building is designed to enable cross-ventilation by inducing the movement of air through the building from the south side to the north side using a passive venturi effect system.  Air leakage is otherwise minimised across the entire structure to reduce heat loss.

h. Passive Heating

As well as the passive solar heat gains, human occupation and secondary heat from household appliances will provide a significant proportion of the heat that these homes will require.

i. Ancillary underfloor heating

Electric under floor heating is used for top up and comfort in areas such as bathrooms, for example.

j. Rain capture

All dwellings would collect and store rainwater for use for non-culinary purposes within the dwellings .  If the geology is appropriate, borehole water extraction could also be used.  These homes would be connected to mains water (for drinking water).

k. Photovoltaic energy generation

All dwellings incorporate PV electricity generation (up to 9,400KWh/year for the larger dwellings).  These homes would be connected to the National Grid to allow them to feed electricity back into it (and draw from the Grid when necessary).  Battery packs would be used to balance out some local demand.

l. Sewage Treatment Plant

Domestic Sewage Treatment Plants are now a commodity item available in many sizes from numerous manufacturers.   As long as they comply with British Standard EN12566-3 they will be certified to discharge to a watercourse.  The Sewage Treatment Plants work by using a combination of maceration, anaerobic digestion and settlement before the water is discharged safely.  This water is then piped to the start of the wetlands area at the bottom of the site where further nutrient and chemical contaminates would be naturally removed.

m. Longevity

High thermal mass structures (concrete, stone, clay and ceramics) survive for thousands of years. Much of the world’s historic architecture is available to us now due to this intrinsic characteristic (the many Roman era buildings that are still standing today are good examples).   These are not homes that will require rebuilding or replacement in 80-100 years but should last instead for many hundreds of years.  This means that the effective carbon cost of construction is much lower, when extrapolated over the lifetime of the home, than a typical UK ‘new build’.