Site Considerations

When considering a site for building an earth sheltered house the preferred orientation for passive solar design should be taken into account. On some sites it may be impractical or even impossible to face the house in the 'right' direction. There are several reasons why this may be the case:

• Site is located on a hill side facing the 'wrong' way (ie. facing towards one of the poles).
• There are fantastic views in certain directions.
• There are appalling views in certain directions.
• The site's relationship to surrounding buildings.
• The direction of prevailing winds.
• Miscellaneous others particular to the site in question.

If this is the case all is not lost, skylights or other alternatives may be used to collect passive solar energy despite the imperfect orientation of the house. However these alternatives are almost certain to be less efficient than if the house was facing in the preferred direction, to what degree this is the case needs to be considered for each particular site.

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As mentioned above the direction of prevailing winds can have an effect on the choice of orientation of an earth sheltered home. Direct exposure to cold winter winds increases the loss of heat from the building, this is due to cold air leaking into the house as well as the wind chill effect. A house that is fully earth-covered in the direction of prevailing winds will be very well sheltered. This will be the case if the wind is coming from behind an elevational type house, if this house is also facing in its preferred direction (passive solar) then it represents extremely good energy efficiency. An atrium style house is also well sheltered from wind in any direction, however, depending on the specifics of the courtyard, wind turbulence may result inside it. In summer it is preferable for breezes to flow through the house in order to cool it.

On some sites these two orientations, shelter in winter, catching breezes in summer, may be different or indeed they may be exact opposites. In this case the climate of the region needs to be considered and it decided whether shelter in winter is more important or vice versa. Once again there may be reasons why you can not, or would rather not, face the house in this direction. This can be accommodated; however it will reduce energy efficiency.

If the site you are considering does not allow either orientation towards the sun or preferable orientation with regard to the wind then perhaps another site should be found, otherwise it must be accepted that the house that is built will not be nearly as energy efficient as it could be. Having said this, such a house may still be more efficient than any conventional house.

It should be mentioned that vegetation, grasses, shrubs and trees, can significantly reduce the wind speed on the ground and can therefore help in protecting an earth sheltered house from the cooling effects of the wind.

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It should come as no suprise that when building an earth sheltered home the type of soil on (or in if you like) which it is to be built is of importance. The type of soil on site can affect the structural design of the house depending on certain characteristics that the soil may or may not possess. The level of the water table will also have an effect on the structure and also the water proofing techniques used. A qualified person, preferably with earth sheltered experience, should take a soil sample at the site in question and consult with your engineer on the results.

"Generally ... most types of soil will not greatly affect the design of the house. The groundwater and drainage characteristics of the site can have a larger impact on the design."

Underground Space Center, Earth Sheltered Housing Design p27.

This is a table showing basic soil types and their suitability to earth sheltered applications. This table is only meant to be a very basic guide and actual soil types will probably not fall into these simple categories.

Table taken from Underground Space Center, Earth Sheltered Housing Design p103.

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