When houses follow nature's ways

Posted Wednesday, December 19, 2012 in Sustainable Maine

When houses follow nature's ways

field mouse nest

by Paul Kando

Earlier, using the metaphor of a walk in the woods, I briefly explored nature’s self-sustaining ways in contrast with humankind’s wasteful use of resources. What if we modeled our economy and management energy on nature’s plentitude rather than human-contrived austerity. What if we gave up our delusion of controlling nature and managed our affairs in harmony with it? (If you missed “Walk in the Woods”, it is posted on www.midcoastgreencollaborative.org  ) Let’s now explore how nature’s ways apply to our everyday needs, beginning with houses.

Squirrels winter in snug, insulated nests which, combined with their own fur and body heat, keep  them warm. The nests are thermal extensions of the body -- animal and shelter form an integrated system. Come spring, winter nests are recycled, nourishing the commons. Nothing is wasted.

Animals curl into a ball and fluff up their fur against the cold, obeying nature’s heat transfer laws. Heat flows from warm to cold. The equation is Q = 1/R x A x DT , where Q is the quantity of heat transferred, R is thermal resistance (reciprocal of U for thermal transmissivity), A is the surface area, and DT is the temperature difference (e.g. between a squirrel’s body temperature and the outdoors). Curling into a ball minimizes the surface area (A).  Fluffing up or flattening the fur varies the insulation value (R) as needed.  A snug nest further increases the thermal resistance (R) of the system centered on the body.

Animals employ diverse energy strategies, depending on their circumstances. Nests built in windless places minimize air infiltration. The Arctic sled-dog’s moisture resistant fur is so thick and fluffy that it permits a comfortable sleep in a blizzard out on the open snow pack. Hibernating animals lower their body temperature: The smaller the DT, the smaller the heat loss and the need for replacement energy. A hibernating bear goes without food all winter. 

State of the art houses built to the international Passivhaus standard mimic these strategies. Like animal nests, they are snug, super-insulated, airtight, yet have a supply of fresh air. They have no thermal bridges (across framing members, for example).  They use less than 10 percent of the heating energy of conventionally built houses. Some of us even mimic hibernating bears: we don sweaters and lower the indoor temperature – and our home’s heat loss. 

What’s wrong with “conventional” houses?  Unlike animal nests and tents of nomads, which serve a short term need, houses are meant to last. Some last for centuries, and all reflect the state of knowledge at the time they were built. In recent decades, unlike our animal cousins, we also lost sight of the purpose of a house, letting it morph from a shelter, to an investment and status symbol in our mind. As investments, we have to build houses as inexpensively as possible and worry more about their resale appeal than their thermal performance. As status symbols, houses fall victim to fashion and fad. Large mansions, tall castles, turrets and towers have always been symbols their owner’s power. In mindless imitation egged on by propaganda, exurban “McMansions” have replaced the functional simplicity of many New England capes and salt boxes, their broken-up roof lines, fancy windows and doors pale imitations of castles of yore. As investors we seek the fastest and best possible return and these visual features cost money. Therefore, false economies are often introduced at the expense of the unseen: poor insulation, poor air tightness, shoddy construction, leaks, thermal bridges and so on. The building process has also changed: marginally skilled subcontractors trying to maximize their own profits replaced old-time craftsmen with their marine-quality workmanship. Building methods have come to mimic mass-production. Oversized heating systems try to make up for quality defects. Some houses perform more like disposable commodities. Quality, no longer a given, now commands a price premium.

The remedy?  Sort out our priorities in harmony with nature’s ways. As home dwellers we want maximum comfort for the least amount of energy consumed. As investors we want a decent return on our initial investment when we sell.  Passivhaus is by far the best at doing both. It is comfortable throughout the seasons.  It costs a bit more to build, but over the expected lifetime of house and mortgage, it costs far less.

Some existing homesteads can be upgraded to Passivhaus energy standards. Others, ideally, would best be replaced. The remainder can be improved 50 to 70 percent. The worst strategy is to deny the shortcomings of your house. Nature’s laws ignored often result in major damage to a structure. Better to (1) bone up on how to upgrade an older house by attending a Home Energy Clinic. (2) Find out where you stand with your home through an independent energy audit. Expect a detailed report on the home’s energy performance, backed up by data, and a prioritized list of suggested improvements along with their cost-effectiveness.  (3) Understand your options.  Make a plan to implement these suggestions on a schedule you can manage and stick to the plan. 

Up next: Houses and the way we think.

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