Science

Building Science: Keeping Elements in Balance

Building science is the study of how buildings function under various environmental conditions. Building scientists study how heat is generated or lost and how to make the structure more comfortable and healthy. Most important, building scientists have learned that buildings work as a system of inter-related elements.

When we try to achieve a healthy and safe building with optimal indoor air quality, the control of heat, air, and moisture are the most important building science elements to focus on (along with health and safety). These five elements are counterbalanced by the envelope of the building and its mechanical systems. The envelope is the actual shell of the building, which includes the structural elements and the insulation.

Occupants are primarily concerned with durability, comfort, and affordability. Occupants affect the durability and comfort of the building by the way they operate its mechanical systems.

The Building as a System

Building science includes several important concepts. First, heat flows from hot to cold. The use of insulation does not control heat flow. Second, heat itself does not rise; warm air rises. This is an important factor in air leakage. Cool air is brought into lower areas of a structure as warm air leaks out the top.

Air leakage is also a comfort problem because it dries out the structure. Warm, moist air leaking out the top of the house is replaced by cool, dry air from outside. If a building is too leaky, or the rate of leakage is too high, the building will be exceedingly dry and unhealthy.

Third, there are three methods of heat transfer: conduction (the molecule to molecule transfer of heat that occurs when objects are in contact with each other), convection (the movement of heat by a fluid), and radiation (the transfer of heat by a hot object without the need of a transfer device or contact, as occurs when the sun heats the earth or when a wood stove heats a space).

Fourth, insulation traps air or other gases, which slows down heat loss. Fifth, building structures "airtight" is a major way to prevent heat loss. A common misunderstanding is that you can build a building too tight. This is not true! You can only under-ventilate it.

Leaky Buildings

In the past, people relied on air leakage to provide ventilation. However, leaky buildings do not guarantee good indoor air quality. Particularly in a cold climate, comfort and health problems result if the building is too leaky. A building leaking air during the coldest part of the winter will cause continuous drying of the indoor air and can lead to increased upper respiratory disease and discomfort.

Leaky buildings also enhance the transport of outdoor pollutants and help them enter the building. Leaky buildings allow for more insect entry as well. High heating and cooling costs result if the building is too leaky, since the heated air leaks out so quickly.

From: Healthy Indoor Air for America's Homes Training and Reference Manual

 

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