When Is a Vapor Barrier Needed?


Vapor barriers often serve as some of the most useful materials for professional builders and contractors as well as installers of new flooring units or tile applications. These rolls of material serve as insulators against humidity and moisture that move between surfaces, whether it's the condensation that builds up on your basement floors or the humidity in your bathroom from showering. However, a vapor barrier is not always needed, so doing a little research ahead of time can save you some time and trouble during installation.

Building Projects

  • A vapor barrier is usually a necessary part of all new building projects. Many wall surfaces, including wood and drywall, are permeable and allow moisture to move freely from them. When the temperature and humidity indoors varies from the temperature and humidity outdoors, condensation forms on the cooler, less humid side as the excess moisture moves from the moist side, which can create rotting in wood components, rusting in steel structures and stains on drywall. The vapor barrier stops this movement from either side of the walls, ensuring a safer and cleaner installation.

Laminate Flooring

  • Laminate hardwood flooring is highly susceptible to expansion and contraction as a result of moisture exposure. Manufacturers require the installation to include an expansion gap between the floors and the surrounding walls, but excess moisture exposure can cause the laminate planks to expand even more than this gap, creating gaps or cracks in the floor boards. This is generally only a problem when the planks are installed over concrete, which can wick and transfer moisture from the foundation of the home. Spread a vapor barrier between the concrete and laminate flooring to prevent the transfer of moisture into the flooring.

Tile Flooring

  • Tile flooring doesn't expand and contract the way that laminate flooring does. Instead, the tiles can crack as moisture seeps in behind them and changes the bonding capability of the mortar that holds the tile in place. Some concrete subfloors are sealed or do not have access to excess moisture, but those that do should be covered with a vapor barrier to prevent the transfer of moisture into the adhesive, grout or tile surface itself.

Other Information

  • Always apply the vapor barrier for a construction application on what is generally considered the warmer side of the wall, which stops the transfer of extra moisture before it even really begins. Installing the vapor barrier on the cool side, or on both sides, will only result in the moisture getting trapped between the wall and the barrier, leading to even worse rusting or mold building. You should always use a vapor barrier under laminate flooring over concrete, but not all concrete subfloors that will support tile require vapor barriers. Perform a moisture test before installation, and consult your manufacturer's instructions to determine if these barriers are needed.

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