Air and Moisture Control in Hot, Humid Climates

Moisture Control in Humid Climates

A well-designed air and moisture control system can add decades to a home’s life, save the home buyers thousands of dollars on energy and maintenance costs, reduce health risks like mold, and generally add to the value of the home and the quality of life and comfort of the buyers.

The best practices for air and moisture control vary depending on climate: it isn’t always cut-and-dry. Climate dictates the primary direction-of-flow for moisture, where moisture is in danger of becoming trapped, and where in the walls it is best to place moisture retarders. In this article we will go over the specifics of proper air and moisture control in warm, wet climates, where constant humidity threatens to erode building materials and promote mold growth.

In hot and humid climates, the largest source of moisture comes from outside air. Infiltrating moisture condenses on cool indoor surfaces, forming droplets of water and promoting mold.

While designers and builders can’t control the occupants’ ventilation practices, you can impact building tightness in important ways. 

Here are a few key points from the “12 Golden Rules for Builders in Warm and Humid Climates” to ensure air and moisture control in climates with high humidity:

  1. Use an air infiltration barrier on the outside of exterior walls. Vinyl coverings or other moisture-retarders placed on the inside of exterior walls will trap moisture inside the walls and promote mold.
  2. Eliminate crevices in exterior walls with tight building practices. The envelope should prevent outside air from entering the stud space and the house interior.
  3. Place a vapor retarder (at least 6 mils thick) beneath concrete slab floors to stop moisture and gases from entering the house. Any tears or holes must be tightly sealed.
  4. Air conditioning and heating ducts should be metal with exterior insulation. Ducts with interior fiberglass linings trap dust, which feeds mold.
  5. Install return air ducts in each bedroom or undercut the doors. Unless bedroom air can enter the return air stream, a negative pressure will form in other parts of the house and pull humid air in from outside.
  6. Provide air circulation into and through each closet and enclosed space via louvered doors, open shelving, or air conditioner supply vents to discourage moisture retention.
  7. Cure poured concrete and dry the structure before applying wallpaper, paint, or floor coverings. Wet building materials can create future problems and destroy the strength of the structure.

Preventing air and moisture infiltration and diffusion is vital in hot, humid climates, where the air is wet and warm. When moisture infiltrates the walls of a structure, the warm temperatures allow mold to thrive, and even more so when it can feed off organic building materials (wood, cloth, or paper).

Mold and other fungi pose serious health risks, as well as threatening the integrity of the structure’s materials. Ensure a tight enclosure and properly placed moisture retarders to protect the life and value of the home.