Vapor Barrier

Definition

A vapor barrier is a membrane used to segregate permeable from impermeable materials, controlling the dew point and preventing condensation problems within a roof system or under concrete floor slabs.

Purpose

Vapor barriers are crucial in building construction to prevent moisture from penetrating walls, roofs, and floors, thereby reducing the risk of mold, mildew, and structural damage.

Examples of Use

• Roof Systems: Installing vapor barriers between the roof deck and insulation to control moisture and prevent condensation.
• Concrete Slabs: Placing vapor barriers under concrete floor slabs on grade to block ground moisture from rising into the building.
• Wall Construction: Using vapor barriers within wall assemblies to prevent moisture from migrating through the walls.

Related Terms

• Moisture Barrier: A material used to prevent moisture from passing through walls, floors, and ceilings.
• Insulation: Material used to reduce heat transfer and control temperature within buildings.
• Dew Point: The temperature at which air becomes saturated with moisture and water vapor begins to condense.

Notes

Proper installation of vapor barriers is critical to their effectiveness. They should be continuous and sealed at seams and penetrations to ensure a complete barrier against moisture.

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