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The New Independent Home
by Michael Potts
from chapter 1 :
The Laws of Physics:
Laws We Can Live With |
If, after consulting the original inhabitants, plants, animals, and humans, we need further guidance, the laws of physics can be called upon to help. Abiding by the same laws, all our various instructors tend to suggest the same solutions. For example, where cold is a major factor, thermodynamics dictates that the best shape will contain the most volume while exposing the least surface: a sphere -- such as beaver lodge and Inuit igloo. Spheres are hard to build using wood and glass, and humans require floor-space with headroom, which is a little different from simple volume, so a rough rectilinear approximation of the sphere, the cube, fits us better. In cold climates, successful human-made houses tend to be cubical. Another example: Animals that do not migrate either take to houses in times of adverse weather (hibernating or aestivating in caves or tree trunks) or are superbly hirsute. My cat's winter coat makes her look twice her actual mass; arctic foxes have even better insulation. Cold-weather creatures are usually smaller and more compact than their temperate relations. So it should be with cold-weather houses, which need abundant insulation and adequate but not excessive space, because the luxury of heating superfluous space is perversely costly.
By anticipating the physical effects of prevailing winds, seasonal moisture, and the warmth of the sun we improve our theoretical model of a house's mechanics. The classic New England saltbox is wider east-to-west, which maximizes solar exposure, and lower on the north side, often sheltering beneath a hill or woodlot for even better wind-shadowing, out of the way of prevailing northerlies. At the heart of a saltbox, a massive fireplace keeps warmth streaming outward from the protected center. If southern windows allow sun to warm the fireplace's mass, the heat re-radiates in the evening, reducing the amount of wood required to counter evening's cold: a simple application of the greenhouse effect.
Heat most often comes to us as light in the form of infrared radiation, which travels in straight lines from its source; once light strikes something -- a surface or an air molecule -- it warms the object struck and the surrounding air. Colder air is less chaotic, and thus denser, or heavier, so it sinks, displacing warmer air, which rises. This circulation is called convection. In a saltbox, the daytime living spaces are downstairs, where active occupancy makes cold tolerable, and bedrooms are above, warmed by the rising warm air; doors at the foot of stairways keep the heat downstairs during the day. Of course these ideas get turned upside down in warm climates: There, a physicist's home will be more spread out, containing more space, narrower and protected by trees on the too-sunny south side, which also has few windows. In the Sun Belt, thermal mass is a good idea only if it can be "charged" with cold during cool nights.
Other physical phenomena inform regionally apt shelters. Wherever summer sun causes too much summer heat, overhangs and deciduous plantings help us tune the home's exposure to the sun, blocking incoming radiation in summer, but admitting more light in winter. In the sticky tropics, where seasonal variation is minimal, the earth's surface is often moist from daily rain and inhabited by insects, because breezes do not penetrate the thick foliage; above the canopy, breezes at the treetop level promise the only relief from the humid heat, and it is sensible to build living spaces on stilts, aligned with and open to the slightest breezes.
After thirty years studying the constantly changing genius of the land I live on, the lessons remain interesting and surprising. Creating a living space, particularly along the margins of wildness, presents a challenge to nature. Even when we provide ourselves with a comprehensive set of findings covering our personal, familial, geographical, climatic, biological, and anthropological requirements in a home, we make some mistakes. The biggest mistake of all, however, would be not to try. Fearlessly, then, since you are now better informed than most architects and builders, turn to chapter 7 and design a home.
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