Earth Sheltered Homes
http://www.eere.energy.gov/consumerinfo/buildplan.html

Saddams bunkers set me thinking... what would it be like to build underground ?

The advantages are numerous

1. Top area can be converted to a tennis court/ mini park
2. Sound proofing , privacy, novelty
3. Less exposure to elements
4. No need of painting, external finish etc.,
5. The temperature of the earth during the summer is much higher at the surface than at greater depths. SO a underground house might be actually cooler.

Did a bit of surfing and the downside seems to be

Cost of construction might shoot up if improperly planned, otherwise it should not cost more than a normal house.

Good design to avoid moisture problems

Design

There are two basic types of earth-sheltered housing
underground
Entire structure built underground.

bermed
The structure built above ground, with walls banked up with earth.

An "earth sheltered" home is one in which the top as well as most of the sides are covered with earth. An "earth bermed" home utilizes a conventional roof, with only the sides of the home protected with earth

From these two basic types, three general designs have been developed. They are the:

atrium (or courtyard) plan ( Love this... might be the one I decide on )

an underground structure where an atrium serves as the focus of the house and the entry into the house

elevational plan, a bermed structure that may have a glass south-facing entry;

penetrational plan, which is built above or partially above earth and is bermed to shelter the exterior walls that are not facing south

An earth-covered dwelling may have as little as 6 to 8 inches of sod or as much as 9 feet of earth covering the structure

" An atrium design offers an open feeling because it has four walls that give exposure to daylight. This design uses a subgrade open area as the entry and focal point of the house. It is built completely below ground on a flat site, and the major living spaces surround a central outdoor courtyard. The windows and glass doors that are on the exposed walls facing the atrium provide light, solar heat, outside views, and access via a stairway from the ground level. Atrium/courtyard homes are usually covered with less than 3 feet (0.9 meters) of earth primarily because there is no benefit in energy efficiency from greater depths. This style also offers the potential for natural ventilation.

The atrium design is hardly visible from ground level and barely interrupts the landscape. It also provides good protection from winter winds and offers a private outdoor space. This design is ideal for an area without scenic exterior views, in dense developments, and on sites in noisy areas. Passive solar gain—heat obtained through windows—might be more limited, due to the window position in an atrium plan. Courtyard drainage and snow removal are important items to consider in design. "
http://www.eere.energy.gov/erec/factsheets/earth.html

The climate in your geographical area will determine whether an earth-sheltered house can be a practical housing solution. Studies show that earth-sheltered houses are more cost-effective in climates that have significant temperature extremes and low humidity

the earth can absorb extra heat from the house in hot weather or insulate the house to maintain warmth in cold weather

In regions with mild winters and predominantly hot summers, a north-facing slope might be ideal. Every site differs, but generally southern exposures offer more sun and daylight throughout the year than north-facing slopes

The site's topography and microclimate determine how easily the building can be surrounded with earth. A modest slope requires more excavation than a steep one, and a flat site is the most demanding, needing extensive excavation.

The type of soil at your site is another critical consideration. Some types of soil are more suitable than others for earth-sheltered construction. For example, the best soils are granular, such as sand and gravel. These soils compact well for bearing the weight of the construction materials and are very permeable, which means they allow water to drain quickly. The poorest soils are cohesive, like clay, which may expand when wet and has poor permeability. Soil tests, offered through professional testing services, can determine load-bearing capability of soils and possible settlements that may occur.

The groundwater level at your building site is another important consideration. Building above the water table is almost essential. Choosing a site where the water will naturally drain away from the building is the best way to avoid water pressure against underground walls. The site should be surveyed for low spots and areas where water will collect. Seasonal or regular surface water flows should be channeled away from the structure. Drainage systems must be designed to draw water away from the structure to reduce the frequency and length of time the water remains in contact with the building's exterior. Underground footing drains similar to or greater than those required by a house with a basement are necessary in many cases.

The "Earthships" are built to be self-contained and independent; their design allows occupants to grow food inside and to maintain their own water and solar electrical systems

Waterproofing can be a challenge in earth-sheltered construction. Keep in mind these three ways to reduce the risk of water damage in your house: choose the site carefully, plan the drainage both at and below the surface of the house, and waterproof your house

Humidity
Humidity levels may increase in earth-sheltered houses during the summer, which can cause condensation on the interior walls. Installing insulation on the outside of the walls will prevent the walls from cooling down to earth temperature; however, it also reduces the summer cooling effect of the walls, which may be viewed as an advantage in hot temperatures. Mechanical air conditioning or a dehumidifier is often necessary to solve the humidity issue. Proper ventilation of closets and other closed spaces should keep the humidity from becoming a problem in those areas.

Air Exchange/Air Quality
Adequate air exchange must be carefully planned when building an earth-sheltered dwelling. Generally, well-planned, natural ventilation or ventilation by exhaust fans can dissipate ordinary odors.