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The building envelope is a critical system that separates the inside of a building from the outside environment. Think of it as the skin of the house, made up of the roof, walls, windows, doors, and foundation. Its primary job is to control the flow of energy, air, and moisture. When the building envelope fails to do its job, it can directly and negatively impact the indoor air quality (IAQ) of a property, often leading to serious health issues for the occupants.
The Enemy: Moisture
The Enemy: Moisture
The biggest threat to a building envelope's integrity, and thus to IAQ, is moisture. Moisture can enter the building envelope in two main forms: liquid water and water vapor.
Liquid Water
When liquid water, such as rain or melting snow, gets into the building envelope, it's a major problem. This usually happens because of leaks in the roof, cracks in the foundation, or poorly sealed windows and doors. When building materials like wood, drywall, and insulation get wet, they become the perfect environment for mold growth. Mold needs three things to grow: moisture, food (which is the building material itself), and an ideal temperature. Once a leak gets into the wall or roof, mold can grow silently behind the scenes, releasing spores and mycotoxins into the indoor air. These particles can trigger allergic reactions, asthma attacks, and other respiratory problems in occupants.
Water Vapor
Even if a building envelope keeps liquid water out, it can still have problems with water vapor. Water vapor is a gas, and it can move through building materials like drywall and insulation. In most climates, there's more moisture in the air outside than inside, especially during humid summers. If this moisture-laden air gets into the walls and hits a colder surface, it can condense back into liquid water—just like the condensation on a cold glass. If this liquid water can't escape and dry out, it gets trapped, and you guessed it—mold will grow. This is why a building envelope must not only be able to keep moisture out, but it must also be able to let moisture dry and escape. If a vapor barrier is installed incorrectly, it can trap moisture inside the wall cavity, leading to hidden mold growth and a contaminated indoor environment.
In short, a well-designed and properly functioning building envelope is the first line of defense against poor IAQ. By controlling the flow of both liquid water and water vapor, it prevents the conditions that allow mold and other biological contaminants to thrive, ensuring a healthier home for everyone inside.
Click the links below to read more about each of the following parts that make up the building envelope
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