Getting to Know Vapor and Moisture Barriers
When warm, humid air meets cold air, condensation occurs, leaving moisture on house surfaces.
Inevitably, a home accumulates vapor from the environment and daily activities such as bathing, cleaning, and cooking. Allowing this vapor and moisture to remain in the house can result in mold growth, a musty odor, metal corrosion, and wood surface rotting. Fortunately, homeowners can use vapor and moisture barriers to prevent this.
Let's explore vapor and moisture barriers:
Understanding vapor barriers
When warm, humid air meets cold air, condensation occurs, leaving moisture on house surfaces. When this moisture accumulates, it can begin to destroy the house structure. Vapor barriers, also called vapor retarders, prevent air from outside entering the house and air in the house from leaving. As such, no vapor moisture can infiltrate walls, ceilings, basements, and floors.
Usually, vapor barriers are positioned close to the side of the building that's warm because warm air tends to move toward cold air. For instance, if a home is in a place with a hot outdoor temperature, the vapor barrier should go close to the outer wall. Conversely, if the indoor temperature is warmer than the outdoor temperature, the vapor barrier must be close to the interior wall.
Understanding moisture barriers
A moisture barrier is more advanced than a vapor barrier because, apart from blocking moisture in the air, it also blocks water from rain, leaks, and underground from infiltrating the house structure. This barrier operates by repelling or diverting water and moisture from where it's unwanted. They are suitable for exterior walls and basement subfloors to prevent the flooring above them from touching water.
Grading vapor and moisture barriers
All moisture and vapor barriers are not created equal and differ in their permeability and materials used. Permeability determines the resistance of a material to moisture, and it's expressed in perms. A barrier with a high perms number is more permeable and will allow some moisture to pass through. Conversely, a barrier with a low perms number is less permeable or impermeable and will restrict moisture from passing through.
Impermeable vapor and moisture barriers are suitable in areas with cold temperatures to prevent vapor transmission. Warm and humid areas require permeable barriers to balance moisture transmission and free airflow. Below are the classifications of moisture and vapor barriers:
Class I barriers: These vapor and moisture barriers have a permeability rating of 0.1 perms or less and are the strongest because they are impermeable. Examples include sheet metal, rubber membrane, and polyethylene sheet.
Class II barriers: The permeability of these barriers ranges between 0.1 and 1.0 perms. They are partially permeable, meaning they let in some vapor. Examples include plywood and 30-pound asphalt-coated paper.
Class III barriers: These barriers allow the most moisture vapor in and have a perms range of between 1.0 and 10. Examples include house wrap, concrete block, and gypsum board.
Keep the house vapor- and moisture-free
Leaving moisture to lurk in the house can weaken the structure and damage valuable assets. A homeowner should consider adding moisture and vapor barriers in high-exposure areas. When selecting the right barrier for a house, consulting a professional in this field is crucial.
Accurate Builders of the Chesapeake provide foundation, basement, and crawlspace installation and repair for the greater Baltimore area homeowners.
