Floor Underlay And Acoustics

What this is

Underlay is the layer between the structural floor and the covering that sits on it. It absorbs small irregularities, softens impact, and is the main opportunity to do something about the noise that travels between floors of a house. Different coverings want different underlays, and using the wrong one shortens the life of the floor.

Telling whether your home needs it

Footsteps clearly audible in the room below, a floor that creaks or feels hollow underfoot, and a covering that has worn unevenly over an uneven base are the common reasons. Lifting a corner of an existing covering usually shows what is there, and whether it has broken down into fragments.

What the job involves

Fix the base first: refix loose boards, punch down proud fixings, and level obvious dips, because underlay is not a levelling compound. Then choose the underlay for the covering going over it, and check whether a moisture barrier is needed for the floor below. Lay it with joints butted and taped rather than overlapped, and think about the total build-up height before you start.

Things to watch

That build-up height decides whether doors still swing and whether thresholds between rooms work; check both before committing. Where there is underfloor heating, only use an underlay rated to pass heat through, since a thermally resistant layer will make the heating ineffective. Soft, thick underlay under a rigid click floor causes the joints to work loose over time.