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| The House as a System A house is made up of many components that work together to form an integrated system. The performance of one component depends on its relationship with other components in the system. Ventilation and heating components, construction materials, methods of assembly as well as the life style of the occupants are all in relationship and effect the whole. They all interact - a change in one affects all others. Replacing or adjusting one component of a house without considering the influence it has on other components and the entire house system can waste energy and money. Creating an air tight building envelope is a method by which all the variables can be maintained in balance. It is becoming widely recognized that many of the failures and warranty callbacks in new construction point to moisture related issues, indoor air quality problems, combustion back-drafting, sooty "ghost" stains on walls and carpets, mold and mildew in homes and buildings. Often this is a result of misapplying new technologies or materials without considering the whole. Air Infiltration and moisture are the biggest culprits. Air Leakage vs Insulation Film Clip Uncontrolled Film Clip Controlled In many homes air leakage is the biggest robber of heating dollars. To increase the economy of heating, most homeowners automatically assume that adding insulation is the answer. However, insulation is not the whole story. Air infiltration can comprise up to 50% of heat loss from a building during winter months. The major sources of air infiltration are are sill plates (25%), wall outlets (20%), and duct systems (14%) followed by windows (12%).* In some instances the sum of all the leaky areas is equivalent to leaving a door open. Houses leak air because of the difference between indoor and outdoor air pressure. The biggest pressure differences are the extremes, the high and low areas in a building. Holes in these areas typically leak more air than holes in the middle. Warm air rises and leaks out any unsealed areas at the top of the building. Leaks inward tend to be at the bottom of the structure, pulling in cool air. This is called the "stack effect". The taller the building, the higher the velocity of air movement in the bottom and out the top, just like a chimney. "Airtight" and properly ventilated homes are more economical and more comfortable to occupy. There are no drafts, only controlled air flow. They are also more durable. In leaky houses, moist, heated air escapes into cooler areas, such as poorly insulated walls and ceilings. There, the vapor condenses on the colder surface, which can cause mold, mildew, rot and other moisture-related problems. Air leakage may contribute to allergy symptoms by bringing in allergens from the outdoors, and by drawing in particulates of loose insulation, dust and organic debris from within the wall cavity. * Energy Design and Construction: A Manual for Energy Efficient and Passive Solar Homes, Governor's Division of Energy report, Colombia, SC, June 1988, P. 9. |
