Sweat Under the Vapor Barrier of My Laminate Flooring

Vapor Barriers Under Flooring

• Since vapor barriers are meant to prevent the moisture in soil from making its way up into your home, you may occasionally find condensation and other types of moisture on either the underside or the top of the vapor barrier. This condensation could be normal and actually sometimes indicates that the vapor barrier is doing exactly what it is supposed to do. But under certain circumstances, this could indicate a problem.

What to Do

• The first step when addressing this issue is to carefully inspect the vapor barrier for any rips or other damage. Vapor barriers used underneath flooring require complete coverage, so any rips in the surface of the barrier could compromise its effectiveness. If you notice any tearing or damage, you will need to replace the damaged portion of the vapor barrier. If there is no visible damage, carefully inspect the top of the vapor barrier; any condensation or sweating on the top of the vapor barrier indicates that the barrier is not working properly and will need to be re-installed. If the condensation appears to be isolated to the underside of the barrier, on the other hand, this only indicates that the vapor barrier is working properly.

Preventing Future Problems

• Even if you determine that you vapor barrier is working as it should, it is wise to take steps to prevent any future moisture problems that could compromise your vapor barrier. Installing a layer of gravel underneath the vapor barrier or underneath the concrete slab below the barrier can provide further separation from the barrier and soil moisture. If possible, adding a layer of sand on top of the vapor barrier serves two benefits by weighing down the vapor barrier to prevent condensation on the barrier's underside and by absorbing condensation that forms on the top side of the barrier.

Other Considerations

• If you are particularly concerned about the effectiveness of your vapor barrier, consider re-installing an alternative barrier material. The most ideal vapor barrier materials underneath flooring include asphalt-laminated paper and polyethylene film, which are often used in conjunction with gravel and sand layers, as noted above. If your current vapor barrier consists of a different material with inferior moisture resistance, it may be wise to install a new barrier using one of these ideal materials.