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Underlay – Glossary

Often used beneath laminate floors, engineered floor boards or solid hardwood flooring. High quality underlay usually takes the form of a foam sheet of approximately 2-3mm thickness on a film backing. The underlay serves as a thin layer of insulation (therefore an appropriate type needs to be considered in under-floor heating situations) but more importantly serves to quieten creaking and knocking ,particularly of floating floors, as they are walked upon. It gives a better quality feel to the finished floor for very little cost outlay. The film backing to the underlay serves as a vapour barrier provided that edges are overlapped by at least 200mm and taped correctly.

In basement and ground floor installations it is advisable to use a more substantial damp proof membrane beneath the underlay.

An alternative type of underlay often used over concrete [where the surface of the latter is not perfectly sound and or flat] is wood fibre. As the name suggests this is a sheet material made from wood and other organic fibres. It is typically laid in sheets of 7mm thickness. It can be used on solid sub-floors having height irregularities up to 2mm. Over and above that the use of leveling compound or plywood onto the sub -floor should be considered.

Wood fibre underlay performs well in terms of heat insulation and sound deadening.