Portland, Maine — The house at 4 Poe Street here sits with its back to the street and at a slight angle to the rectangular lines of the plot. Most visitors wonder why. So owner-builders Peter and Susan Martelle are happy to explain: The demands of the central heating system, they say, dictate that the house face as close to due south as possible.
Put another way, the Martelles rely largely on the sun to heat their home. It does this most effectively simply by shining in through the windows. There are no fans to circulate hot air or pumps to move sun-warmed water, no rock-filled basement for heat storage.
Simplicity is the key to everything in this low-cost passive solar home. Moreover, this very practical and straightforward design has proved itself over the centuries. It is a "saltbox," among the more commonplace house designs in pre-petroleum New England.
Just how effectively the Martelle saltbox works is shown in the annual heating bill for the last three winters -- the cost of 1 1/2 cords of wood a season.
In maine, firewood is still relatively inexpensive. But even elsewhere, at $ 200 a cord, the heating bill would still be dirt cheap by today's standards. In wood-short regions, coal could provide inexpensive backup heat. Even electric resistance heat would not prove exorbitant in a home that traps the sun's heat and holds it as effectively as this one does.
When the new married Martelles sought a home of their own, they hadn't the money to go out and buy one. So they enrolled with the Cornerstones Institute in nearby Brunswick and learned how to build their own. Just as important, they learned about energy-efficient designs and that some of the most effective were among the least costly to build.
In deciding on the type of home they wished for themselves, the Martelles looked back to a time when cheap oil or gas was not available and when New englanders generally could not afford expensive housing. In other words, when people "were in much the same position as we find ourselves today," Peter Martelle says.
Among the most efficient and inexpensive designs to be developed during that era was the saltbox. So the Martelles chose that concept and Susan drew up the plans, bearing in mind two cardinal principles of effective passive solar design: 1. South-facing and therefore sun-facing windows and 2. good insulation in the ceilings and the walls to prevent rapid loss of heat once the sun goes down or the fire in the stove goes out.
The first of these principles adds nothing to the cost of construction and the second is the most cost-effective action in home building today.
The saltbox has a long sloping roof facing the north -- to shed against wall to let in the sun. The Martelle home has one-third of the south wall given over to windows. In winter the sun streams in to within some 7 feet of the back wall; at the height of summer it comes in a mere 2 feet.
Small east and west windows let in some light but exist principally to provide cross ventilation in warm weather.
Peter gives his wife full credit for her design.
"I knew it would work well," he says of the house they have lived in for the past three winters, "but I never dreamed it would be this efficient."
The sun, along with a relatively small wood stove fired only a few times even on the worst of winter days, provides comfortable warmth.
"I put in plenty of amperage when I built this house," says Peter, "so I could install electric resistance heat if necessary. I was pretty sure I would need it in prolonged cold spells." But that precaution wasn't necessary. Even in the record cold of last January the house was tight enough, and well enough insulated (6 inches of fiber glass in the walls and 9 inches in the ceiling), for the small stove to hold its own easily.
"We never burn a fire in the stove after we have gone to bed," Susan asserts.
In the Martelle house it isn't necessary. On several occasions last January the couple would retire with the stove damper shut and the temperature at about 70 degrees F. The next morning, even with the outside temperature at zero, the house "would be somewhere in the mid-50s." A quick firing of the stove would quickly warm up the 1,200-square-foot home, and "then the sun would take over."
Even on the coldest of days, if it is bright and clear, Susan dresses in light summer clothing -- "often in my jogging shorts," she smiles -- such is the warmth of direct sunlight.
"It's like having someone else pay most of your heating bills," Peter says of well-insulated homes that face the sun.
On the February evening I visited the Martelle home, it had been an unusually mild day (in the low 50s) for the time of year. But there had been no better than partial sun all day long. Even so, the home was a comfortable 70 degrees on sun power and whatever heat the human occupancy and cooking had generated. There had been no fire in the stove that day, nor did they plan to light up after I left around 8:30 in the evening.
"It won't be necessary," they both agreed.
It cost the Martelles around $20,000 to build this two-bedroom, 1 1/2-bath home. According to insurance estimates it would cost a little more than twice that figure to have an outside builder replace it.Even the latter figure is low by todays standards.
Peter recalls how the bank refused to believe he could build at so little cost. The Martelles had $5,000 and asked the bank for $15,000.
"You'll never do it for that price," the loan officer said as he insisted they take $20,000 or there would be no loan at all.
The Martelles did indeed build the house within their estimate and returned the unused $5,000 to the bank. But it bothers them that they had to pay interest on the money they did not need.
If there is one flaw to the Martelle design, according to contempory thinking , it is a lack of much conventional thermal mass (interior stone or brickwork which absorbs heat when the house is hotter than needed and releases it when the house cools down). But the heat storage provided by the house itself (even wood will absorb and radiate heat) has proved perfectly adequate in this New England climate.
"Perhaps thermal mass becomes more critical in the hotter regions of the country," Peter concedes, but it isn't that important here.
It was this lack of conventional thermal mass that failed the Martelle design when it was entered in a Department of Energy competition for passive solar homes. But Susan points out that every one of the winners (there were more than 30 of them) were intricate and outrageously expensive to build, in her opinion.
"Our house has shown that passive solar not only works, but that it is inexpensive as well," the Martelles agree.
Others might describe it as downright cheap.
Plans of the Martelle-designed home are available through Cornerstones Energy Group, Brunswick, Maine 04011.m