A vapor barrier under laminate floor, required for most laminate flooring installed over concrete. This vapor barrier which is actually a vapor retarder helps to keep moisture vapor from entering into the laminate floor. Concrete substrate must be tested in accordance with the flooring manufacturers instructions. Excessive moisture can be found in a concrete slab of any age. Not all manufacturers require the same tests and not all floors are the same. All-in-one laminate underlayment cushions with a vapor retarder attached are available.
A Vapor Barrier Under Laminate Floor Reduces Damage
Interior Vapor Retarder Over Concrete Subfloor
When a laminate floor is installed over a concrete subfloor a moisture barrier must be used. Most every laminate manufacturer will require a vapor barrier under laminate flooring. Not sure, check the manufacturers installation guide for the flooring that you are installing.
Failure to install a proper vapor retarder over concrete will likely result in a floor expanding. This will cause laminate floor problems such as cupping and gaps.
Always check a manufacturers installation instructions prior to installation to assure that proper procedures are followed and proper materials are used.
Do Not Use a Vapor Barrier “Retarder” on Wood Sub Floors
It is important to note that you DO NOT install a vapor barrier under laminate floor that is installed over a wood subfloor. Over wood a vapor barrier will trap moisture and cause damage. Some laminate underlayments are a combination of vapor barrier and foam so take care in selection.
While most manufacturers, NALFA and NWFA flooring associations do not recommend the use of a vapor barrier (moisture retarder) over wood subfloors their are laminate manufacturers such as Harmonics that do. If the manufacturer of your laminate products requires you use their moisture barrier over wood, use it, but ONLY the moisture barrier they say to use. Be sure to follow their installation directions carefully. Harmonics for example states, “For wooden subfloors, cut the moisture barrier 1 inch from the wall.” The reason for this is to give any trapped moisture trapped below to have an opportunity to gas off at the side of the wall. This is unlike the requirement to run the moisture barrier up the wall when the laminate floor is being installed over concrete.
A foam or other type underlayment approved by the laminate manufacturer needs to be used for installation over wood subfloor.