I have been a long-standing fan of underground or at least earth sheltered buildings. Depending on your definitions, this mode of construction is either rare, or quite the opposite, almost everywhere.
Setting aside the obvious vernacular traditions of troglodyte homes in the soft tufa of Cappadocia in Turkey, Yaodong in China, or even the Rochemenier troglodyte farms of France, building entire dwellings underground is uncommon. But some places on earth consider it entirely natural to build basements for every building; so it is not for lack of understanding of either the building technology, or of the environmental advantages of earth sheltered construction, that the building type seems to figure so little in the magazines and more scholarly architectural literature.
I came across one just recently in Detail, that reminded me of all the reasons why we should be considering earth-sheltered construction much more often. This project was motivated, as it often is, by the problem of inserting quite large additional accommodation in a setting where the local planning authority is extremely restrictive with respect to what is allowed to be built in a sensitive conservation area:
The house in question, an old one picturesquely situated at the top of a 2,400-square-metre sloping site, is located not far from the historic town centre of Germain-en-Laye in the western environs of Paris. The buyer needed more than the 100 square metres of living space that the building could provide for his large family, yet the grounds, which include a huge old lime tree at their heart, were not designated for development. The task of the architects was thus to resolve this conflict.As the article goes on to say, "the planners came up with a design that practically disappears into the earth, and thus managed to fulfil the client's wish while reconciling it with the need to preserve nature and keep the property unbuilt. The information that it would barely be possible to see the house extension from public areas or on Google Earth swayed the local planning authority, and a building permit was duly granted".
On an ideally oriented sloping site, it is possible to cut into the slope with intelligent excavation, build simply in good-quality reinforced concrete, use waterproofing strategies that have the best chance of longevity (because by definition they are to be protected from exposure to the usual enemies of ultraviolet degradation and physical abuse), and thereby to create economically bright, sunny spaces which typically require almost no supplementary heating or cooling.
The house in Saint Germain-en-Laye is a very good example of most of these advantages. A rambling, relatively narrow incision into the slope produces short structural spans that are supported almost invisibly by slender perimeter steel columns integrated into extensive glazing. The free-form plan creates all the spatial excitement that you would want to live with, while pragmatically responding to the protection area around the mature existing tree. It is worth thinking briefly of the stated project cost, in comparison to what it might have cost to build conventionally the same area at the same quality.
It is a pity that there is almost no information on the environmental performance. But I am fairly confident in guessing that the space performs almost stereotypically for optimised passive solar heating, with its combination of well-oriented vertical glass and exceptional surface areas of thermal massive walls. Intuition allows us to grasp the likely advantages for summer cooling, but most people would be at a loss to work out why such construction is ideal for both summer and winter.
The quickest way of understanding how that might be so is to remember that the significant amount of earth shelter has one main consequence: it evens out the temperature swings between the highest and the lowest, both daily and seasonally. So if you want to estimate what is likely to be the steady, narrow temperature range in such spaces, you have a good guide by looking at the average yearly temperature for the location.The sort of technical refinements that a well informed designer can bring, to this already likely favourable circumstance, are surprisingly simple:
- If the region's average temperature for the year is too low, orient your glazing for effective free solar heating, and if necessary 'uncouple' some of the surrounding earth, by partially insulating behind the walls;
- If the yearly average temperature is a little too high, you can get extra overall temperature depression from the evaporative cooling produced when you irrigate the vegetation overhead.