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How Your Home Works

The House as a System

Until fairly recently, designers and builders considered each part of a house – foundation, walls, roof, windows and doors, plumbing and electrical systems, heating, ventilation and air-conditioning systems – independently. Experts at Natural Resources Canada have gained a lot of experience with energy-efficient building over the last three decades. One of the most important lessons is that the house works as a system. Each part of the house is related to all other parts, and making a change in one place causes an effect somewhere else.

There are many forces at work in a house: structural loading, the effects of wind and weather and flows of moisture, heat and air. These must be kept in the right balance. Adding insulation, air barriers and vapour barriers can affect moisture conditions, ventilation and combustion air. That is why the house-as-a-system approach considers not just the individual parts but the interaction of the house, its equipment and systems, the occupants and potential weather conditions.

The research that led to the development of the R-2000* Standard showed not only that the various parts of a house work together as a system, but that this system interacts with both the surrounding environment and the occupants. The overall comfort, durability and energy efficiency of a house depends on how well the system works.

The concept of the house as a system is best shown by example. The supply of fresh air in a house was once considered a simple matter of opening a window or of assuming that there were enough cracks and leaks in the home's exterior to provide fresh air. For much of the year, though, such uncontrolled ventilation causes higher heating costs and cold drafts. Conversely, in a home that has an airtight construction but no ventilation system, moisture and other pollutants caused by everyday living could build up and cause air quality problems. Poorly ventilated houses often have stale air that's full of moisture from everyday living. This constant high moisture can result in condensation and mould growth that compounds the poor air quality problem.

Another reason air leakage remains so important is how it can affect your home's durability. Warm, moist air from the interior leaking into the wall cavity can result in condensation within the cavity. This may reduce the effectiveness of any insulation and affect the durability of the structure.

*R-2000 is an official mark of Natural Resources Canada.