Greenwood, Maine — I have begun to appreciate some very positive things about the piece of mountainside I bought here in Maine. It appears to be considerably warmer than the latitude (44 degrees N.) says it should be. In fact, light frosts were settling in gardens just a few miles west of Boston this past fall several weeks before anything similar struck here, about 100 miles to the north.
The terrain and its relationship to the sun is the reason for this warmer-than-expected site. The land slopes fairly steeply to the south-southwest. In other words, it faces the sun; and because of the slope, the sun's rays strike it more directly than they do flat ground. As a result, the land absorbs considerably more heat throughout the summer months, and this residual warmth carries it over for a longer period in the fall. In winter, too, the more direct rays make it a warmer place to be whenever the sun shines.
The slope plays another positive role: It makes it possible for cold air (which flows like water on windless nights) to drain away into neighboring valleys. The effect of this was brought home to me last fall when a valley some 15 miles away had its first freeze before even the lightest hoarfrost brushed the land hereabouts.
As holdings go in this rural area, my acreage is modest, but it is much bigger than anything I have owned before.
I found that choosing a building site that makes the best use of the sun was relatively straightforward. In fact, in energy-efficient housing construction, the very first step is to choose the right building site. Whether your land is large or small, the first priority is to decide just where the house will go and which way it will face. In this new age of efficiency, the picture windows don't necessarily face the street anymore.
The idea, of course, is to make maximum use of whatever solar energy falls in your area. To do that, consider the following:
* Look for a moderately sloping building site that faces south. This is the ideal, but southwest or southeast is also very effective. The accent here is on ''moderate slope.'' Steeply sloping sites make excellent use of the sun's energy , but they are more costly to build on.
* Choose a site that is free of shade from 9 in the morning to around 3 in the afternoon. Watch out for trees (even leafless deciduous trees can shade out between 30 and 60 percent of the sun's energy) and any neighboring buildings that might be in the way.
* Avoid low-lying locations, where cold air settles at night. Also avoid the brow of a hill, where wind speeds are frequently 20 percent higher than on any of the sides.
If yours is a city or suburban lot that is both small and flat, your options might be limited. But note where the sun shines, and place the house on the most northerly section of this sunny location. This will reduce the potential for shading by any future building that goes up on a neighboring lot.
The house and its largest windows should always face the sun, but remember to use discretion. True south might be the best theoretical direction to face a house, but you will base your decision on the amount of sun that is available to you. If afternoon shade is a problem on your lot, then face your house a few degrees to the east; if morning sun is the problem, then face the house toward the west.
I was told recently of a young woman who steadfastly set her mind against any form of solar house because she felt she could not afford anything more than a factory-built, modular home. She had the house delivered and placed on the foundation so that it faced the street, which wasn't the most energy-efficient option she had.
There is nothing wrong with modular homes. Indeed, they provide some of the best value for the money available today. But even a nonsolar home uses far less energy if it is bathed in the sun all winter long and if its principal windows face the equator. To have less is inexcusable in this day and age.