Green Comfort in a Green Home

Home Building and Sustainable Living
By: Michael Roberts - Friday, November 18, 2011
Source: iGreenBuild.com

As interest in Green Building and Sustainable Lifestyles grows the result of now irrefutable evidence of the accelerating rate of global climate change we are being inundated with huge amounts of information. Not surprisingly, at least some of this information is incorrect or misunderstood.

One of the most misleading contentions is that green living, and in particular, green housing, will require one to compromise personal comfort. Nothing could be further from the truth. In fact, a green home is not successful unless it actually enhances the comfort of its occupants.

Green building is also sometimes known as sustainable building or environmental building. Most simply put, the idea of sustainability, or ecological design, is to ensure that our actions and decisions today do not inhibit the opportunities of future generations. Green building is the practice of increasing the efficiency with which buildings and their sites use and harvest energy, water, and materials and reducing building impacts on human health and the environment through better siting, design, construction, operation, maintenance, and waste disposal the complete building life cycle. Sustainable means using methods, systems and materials that won't deplete resources or harm natural cycles. Sustainable housing is housing that is safe, healthy and life enhancing. A sustainable design has positive impacts on the occupants, the builders, and the Earth. It is resource efficient, durable and adaptable to future eventualities. Green Building is largely about how well and how long buildings perform: design efficiency and durability.

Comfort is too often regarded as an intangible quality, something we know only when we feel it. But in scientific terms, it can be described and designed - with surprising precision. BUILDING GREEN IS A SCIENCE. One’s perception of comfort depends primarily on maintaining a thermal environment in which the body’s heat production is in equilibrium with its heat loss, so that neither “shivering” nor “sweating” occurs. And the extensive science available to us allows us to describe, modulate, and enhance human comfort in an enclosed space. We seek to optimize humidity levels and heating efficiency to enhance general health without creating an environment leading to excessive condensation or support of pathogens such as molds and mildews. We seek to regulate air temperature to control the levels of convective air movement (drafts) while minimizing the stratification of temperature vertically within a structure (warm air rises). We seek to minimize the rate at which interior objects, including people, change temperature through judicious use of materials with high thermal inertia (typically meaning dense materials). And, most important of all, we must assure that the air we breathe indoors is pure, fresh, and free of pollutants and allergens. A GREEN HOME IS A HEALTHY HOME.

Naturally, we all have other objectives that affect the quality of a structure as well, most of which are related to individual lifestyle. In this article, however, we will dwell only on those variables that apply universally to the attainment of what we might refer to as body comfort.

One of the biggest challenges to creating a comfortable home in the climate of Routt County is based on simple geometry. High snow loads and deep frost lines mean that it’s more cost-effective to build up than out, since walls are cheaper than either roofs that sustain severe accumulations of snow, or foundations affected by deep frost penetration, hard rock removal, and oftentimes expansive soils. But building "up" increases the tendency for temperature stratification - warm air rises, resulting in lower levels being too cool and upper levels being too warm. The simple - and very inexpensive - solution is to incorporate an air recirculation system just a low power fan and duct moving warm air from the top of the house to the bottom of the house, thus destratifying, or even-ing, temperatures throughout the house. The entire loop is inside the house; there is no connection to the outside. Thus we are increasing comfort levels without either heating or cooling the house, but simply redistributing the air and no energy is expended except the minute amount used to operate a very low-volume fan. Simple. Comfortable. Green. Every home should have one.

But building up instead of out also creates a design commitment to incorporate multiple levels of stairs and invariably a footprint too small to accommodate a master bedroom suite on the main level (where we’ve already committed to living, dining, kitchen, and entry areas). These are two increasingly unacceptable options today as baby boomers anticipate longer life spans, along with the associated longer periods of lessened, late-life agility, than previous generations. When we choose to build out more ranch style not only do we increase the cost per square foot of a building, remember roofs and foundations cost more than walls, we also increase the rate of heat loss from the structure. Since heat loss is a function of the exterior surface area of a structure, the greater the surface area of a shape for a given interior volume, the more costly it will be to heat. Consider that the shape whose surface area-to-volume ratio is the smallest is a sphere. For obvious reasons, it is neither cost-effective nor practical to build homes in the shape of a sphere. The next best shape is a cube, in which, like a sphere, the vertical and horizontal axes are the same dimension. Every additional corner or indentation designed into the cube increases both the surface area and, hence, the rate of heat loss as well as construction costs. In advising a client about the projected costs of construction, it is essential that the Architect and/or Builder point out the significant impacts these types of choices can have. Not all square feet are created equal.

Thus, among the most important and certainly the single most frequently overlooked - objectives of quality home construction is the optimization of all the variables that affect temperature equilibrium (i.e., comfort). Since it is inevitable that some amount of temperature change is unavoidable when objects of different temperatures interact such as the inside and outside of a building it should be obvious that the more slowly that temperature changes and departs from the optimum equilibrium condition, the more easily we can resist that change (by adding heat from a boiler, for example) and restore the desired equilibrium comfort zone (think of a swinging pendulum; the slower it’s swinging, the less effort it takes to restore it to its center, or equilibrium, position). Buildings lose heat in three ways by conduction through solid materials (which we resist by using varying types and thicknesses of low-conducting insulation), by convection, or air movement (which we resist by sealing infiltration holes in the building envelope), and by radiation, or the transfer of heat by electromagnetic waves (which we resist by using a variety of reflective surfaces, like those applied to window glass or the backing on insulation panels and batts). The more we understand about how heat is transferred, the better equipped we are to minimize the changes that disrupt our comfort.

Now of course there are myriad other variables that affect the energy efficiency (and comfort) of a home - like glass area, orientation to the sun, shading, insulation type and thickness, prevailing wind direction, density of construction materials, leakiness of the house, number of occupants (and the heat they radiate). The science of building has mostly to do with controlling all these variables in a predictable manner so that when one is changed, the others do not get thrown out of balance and rot timber, dry mucous membranes, or form ice on the inside of windows.

It should be clear, then, that the more energy efficient the structure, the lower the operating costs, the slower the rate of temperature change, the greater the comfort, and the lower the volume of greenhouse gas emissions resulting from the combustion of fossil fuels thus slowing the increasingly disturbing rate of
climate change. Terrific! But something is missing. Over the years, it has always been assumed by Building Code officials that the leakiness of an average home was sufficient to assure adequate fresh air inside the building envelope. But this assumption has been made obsolete by the quest to maximize energy efficiency, which dictates an airtight building envelope. One dramatic example of building science run amuck is what happened to homes when the application of recently invented, synthetic stuccos began in the 70’s. The material was generally selected because of its durable, low-maintenance qualities. The horrific oversight was that this membrane-like coating also started making homes more airtight. Since these homes no longer breathed (or leaked) as was previously customary, they retained not only heat, but also moisture and a wide array of indoor air pollutants. And MOLD happened. And structural wood components rotted. And people got sick, and lawyers got rich. Comfort was being seriously compromised in the name of green building - not good press for the emerging movement. This is a good example of the Law of Unintended Consequences (also known as Murphy’s Law).

Science, including Building Science, aims to identify all the variables within a system, control and predict the way in which they interact, and avoid unintended consequences. In the effort to make homes more energy efficient by tightening the envelope and reducing air infiltration, indoor air quality (IAQ) has too often been unconsciously compromised leading to high levels of indoor air pollution and resulting in our increasingly high rates of immune-system related illnesses, allergies, colds, respiratory complications and worse. Green, perhaps, but not healthy and certainly not comfortable.

Only in the past decade or so has the science of building finally reconciled the conflicts between efficiency and comfort through its focus on the Healthy Home. The problems associated with minimizing heat loss are now resolved by advances in the technology of regulating indoor air quality, minimizing temperature swings, and controlling moisture transport. Mechanical heat recovery ventilation (HRV) systems assure adequate replacement of polluted indoor air with fresh outdoor air with minimal heat loss. Every home should have one. Central vacuum systems are no longer a luxury but an essential and integral component of Healthy Home design, removing from the house the allergens and other critters that thrive in carpet fibers. Every home should have one. Use of materials manufactured with low levels of volatile organic compounds (VOC’s) has reduced pollutants and associated allergic reactions inside the home. Radon testing and mitigation should become a standard practice. There are several areas in Routt County that have excessively high levels of radon. There are many more recycled, renewable, durable, chemically inert products that have entered the mainstream market place in recent years as their acceptance has increased production levels and reduced prices enough to make them competitive with conventional alternatives. There’s no reason we shouldn't’t be using them as standard practice.

In conclusion, we must learn to view the home as a total system comprised of many highly interrelated parts and systems. It behaves much like a living organism, responding in predictable ways to environmental stimuli, both internal and external. By understanding the variables that influence that response, we can regulate and stabilize the response. And live comfortably ever after.
A Green Home is a HEALTHY HOME, and a Healthy Home is a
COMFORTABLE HOME.

Bio: Michael Roberts is a long time resident of Steamboat Springs and an avid skier. He is also the president of Habitat Construction.

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