Flooring Underlay is the term for a thin material laid between the subfloor and the floor. Flooring Underlays are useful for stability, insulation, sound reduction, and moisture protection. Flooring Underlay is commonly used for floating wood floors. Fixed floors do not usually incorporate an underlay as they are fixed directly to the subfloor.
A Damp Proof Membrane or DPM is a waterproof barrier that's introduced between your subfloor and your Timber Flooring. Effectively a thick plastic sheet, a damp proof membrane (DPM) is used to create a barrier between a concrete (or screed) subfloor and a Timber Floor.
When installing Timber Flooring, solid or engineered, on a concrete base the use of a Damp Proof Membrane is always recommended. No matter how dry your Timber Flooring feels it will always contain dampness, which can be drawn to the wood if not treated causing cupping, lifting and general damage to the floor. For engineered flooring use a plastic membrane sheet exceeding 0.2mm. For solid floors, a 2 part liquid Damp Proof Membrane should be used.
