Passive design includes positioning your house for greatest passive solar gains: having excellent insulation, selecting the most energy efficient tools for heating and cooling and choosing energy efficient appliances.
Focusing on real costs and savings, Home Sweet Zero-Energy Home by Barry Rehfeld (New Society Publishers, 2011) is a practical guidebook that clearly identifies all the pieces of zero energy homes and explains how homeowners and buyers can take smaller steps towards reducing the energy use of existing buildings. In this excerpt from Chapter 2, find out how to use passive design to site your house properly for maximum passive solar gain.
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The two-story home on the south side of a straight flat stretch on a road outside of Urbana, Illinois, appears to be as much a part of its rural environment as the ground surrounding it. Large stone bases support beams holding up a porch roof at the front and eastern and western sides of the house. The siding is a combination of earth tones. A three-foot-high strip of brown gives way to the brownish-gray color of the roof. Its sharp square shape and low gabled roof gives the home a solid imposing look of midwestern permanence.
Yet while it seems, like many homes in its area, to have been planted on its foundation and been quietly blending into its surroundings for a long time, that image is deceiving. This Urbana home was completed in 2008, and its shell or envelope is not just standing there, but is very busy reducing the amount of energy needed to run the home.
This work is done just by the way the home is designed and built, a concept known as passive design. The idea is that by incorporating a few relatively simple features into the house it will make the most — and, when wanted, the least — of the sun’s energy. Passive design succeeds best when it allows as much of the sun’s heat in as possible through its windows during cold months and keeps it out in hot months. Good passive design also allows sunlight in through the windows, while keeping the wind from penetrating the seams around them or anywhere else in the house’s structure all year round.
Letting the sun through the home’s windows in the winter means a homeowner can bask in its warmth and natural light while paying smaller utility bills. Keeping it from shining through the windows in the summer means the cost of running air-conditioning systems will be less.
Passive design could just as easily be called simple design. Its focus is on not complicating a few mostly basic features common to all buildings. These include orientation, shape, size, insulation, windows, doors, ventilation and landscaping. There are no moving parts to contend with, except with ventilation and, to a lesser extent, windows.
Good passive design is desirable throughout most of the country because the sun’s heat and light can contribute to energy efficiency almost everywhere. Where there isn’t much of a need, if any, for its heat indoors, as in the Deep South and parts of the Southwest where cooling predominates, developers may decide in favor of having little or no direct sunlight in the house all year long.
Passive design begins with site selection. Ideally, it’s best to have a site where the southern boundaries of the property are unobstructed and the entrance to the home will be on the eastern, western or northern side.
The light from the sun entering Earth’s atmosphere spends most of its time in the northern hemisphere shining on the southern face of anything it strikes. An unobstructed window facing that direction — plus or minus 20 degrees, which at the greatest deviation will still provide 92 percent of the sun’s heat facing due south — allows more of the sun’s energy to pass through during the course of the day than a similar window located on any of the house’s other sides. (In the southern hemisphere, it’s north-facing windows that do best.)
The ideal, however, is as rare a commodity for zero energy homes as it is with most things in life. Roughly speaking, less than 25 percent of home sites qualify.
Take a typical housing development, the kind built by major home-building companies that are laid out on vast tracts of land in grid-like formation. The classic example is Levittown, New York, built between 1947 and 1951. More than half a century later, the tradition of building large planned communities continues. The top ten builders in the US, which includes D.R. Horton, Lennar, Pulte and Centex, alone build 25 percent of all new homes, and that percentage is expected to rise to 33 percent in the coming decades.
Mass producing homes laid out on a grid leads to the same exposures repeated time and again. The grid may not be obvious from the ground level. It may be rectangular, irregular or both, like the planned community built by D.R. Horton in Windsor, Colorado, or the one built by Lennar in Waretown, New Jersey, but several left or right turns will quickly bring a driver back to where they started.
For example, think of the streets in one of these communities that run north and south. The homes will generally have their windows facing east and west, to the street and the backyard, with few windows looking out on their neighbors on the north and south sides. The other two streets in the grid — the ones running east and west — will have just the opposite arrangement. Most of their window area will face north and south. That gives both the potential for maximizing the southern exposure, but only those on the north end are, for all practical purposes, in a position to realize it. Their south sides — the backyard — are not going to have entrances or garages taking up potential window space, and they offer better privacy for bedrooms and living rooms, which get the most window area.
If the grid is square, then 25 percent of the homes will likely have the ideal. If it’s a rectangle, it would be more or less than 25 percent, depending on whether the length of the grid runs north and south (less) or east and west (more).
While facing a core of backyards may be the most common way to secure an open southern exposure throughout urban and suburban tracts of homes, it’s not the only way. Move up the economic ladder and builders can utilize strategies to orient more homes to the south by developing cul-de-sacs. This way, the entrance road and the homes can be arranged so as to give the homes a southern exposure while also endowing them with a bit of individuality and perhaps more privacy.
Sometimes though, nothing will work. Tall buildings, trees and hills or mountains can stand in the way of the southern exposure. There are also times when no matter how open a site is to southern exposures no one could be blamed for ignoring it. This could be the northern developer who opens his homes to beautiful vistas of mountains, lakes or urban skylines to the north — braving its brutal winter winds — while turning the back side of their houses, where they install garages and utility rooms, over to highways, shopping malls and other developments. More simply, the southern exposure just may come at too high a price for reasons that may or may not have anything to do with its exposure.
There are times when even a southern exposure, even one with a great view and an affordable price, should be turned down. This could be the case when the choice is between developing virgin land or an infill. The main difference between the two is that in the former the land hasn’t been developed while the latter has been at one time or another. An infill may be a site where a house burned down, or is abandoned or condemned. An infill might be created when a homeowner puts a piece of their property up for sale or an oddly shaped vacant lot between two developments becomes available. Yet another is when a commercial or industrial lot gets zoned for housing. The US Census began tracking density for the first time in the 2000 Census, signaling a growing interest in managing land use better.
What unites infills is that developing them will be more energy efficient than opening up virgin land for a variety of reasons. No energy will likely be expended preparing the land for development because it was likely to have been leveled before. Water, sewage and gas and electric utilities will probably all be in place or reasonably accessible. Public transportation, shopping, entertainment and schools will generally be nearby.
The decades-long decline of inner cities in the Rust Belt where boarded-up homes, closed factories and vacant lots are common provides opportunities for developing infills. More recently, the collapse of the speculative housing market in 2008 that left developments unfinished — with capped sewer connections sticking up out of the ground — has extended the potential for developing infills to other parts of the country.
Virgin land, however, will take a lot of energy to develop, and there’s less of it with each passing year. A stand of trees may have to be cleared for nothing better than kindling, which means it will literally be going up in smoke, thereby adding carbon emissions to the atmosphere. A septic tank and well will probably have to be installed, and electric utility lines will have to be brought in, increasing the burden on existing systems. The homeowner will also expend more energy living there. Further away from most places they want to reach, they will be spending more time burning fossil fuel by driving to wherever they need to go.
Germany is able to do it because orientation is just one facet of passive design. Some sacrifice or compromise may be required elsewhere in the building process without the perfect southern exposure, but that’s exactly how zero energy homes are developed. Give a little here; get some somewhere else.
This excerpt has been reprinted with permission from Home Sweet Zero Energy Home: What it takes to develop great homes that won’t cost anything to heat, cool or light up without going crazy published by New Society Publishers, 2011. Buy this book from our store: Home Sweet Zero Energy Home.
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