Lay underlay for a floating floor on a timber floor
Prep the timber floor, check for damp, then roll out and tape underlay ready for a floating floor.
FU-01Clear the room and check the floorRemove furniture, rugs and skirting-mounted trims if you're taking underlay right to the wall. Walk the whole floor and check for loose boards, springy spots, or boards that flex underfoot. Punch down any nail heads or screw heads that sit above the surface with a nail punch, and drive in or remove any protruding fixings.
FU-02Check for damp before you cover the floorA suspended timber floor should feel dry and smell neutral, not musty. If you have any doubt, test a few boards with a moisture meter — readings above about 18% suggest a damp problem you should sort first, such as blocked airbricks or poor sub-floor ventilation. Covering a damp timber floor traps moisture and can lead to rot, so don't skip this if the room has ever felt cold or smelt musty.
FU-03Sand or plane any high spotsUnderlay will telegraph small bumps through to your finished floor, so flatten any obvious high points where boards meet unevenly. A hand sander or block plane on a raised edge is usually enough. Vacuum up the dust before moving on.
FU-04Sweep and vacuum thoroughlySweep the whole floor, then vacuum into the gaps between boards to lift grit and old debris. Any hard particles left under the underlay will wear through it over time and can show as a bump under your new floor.
FU-05Choose the right underlay for your flooringCheck what your flooring manufacturer recommends — laminate and engineered wood usually need a foam or combi underlay, sometimes with a built-in damp membrane; vinyl click flooring often needs a thinner, denser underlay. Using the wrong type can void the flooring's warranty, so check the flooring box before buying underlay.
1 roll · Underlay roll (type per flooring manufacturer)
FU-06Roll out the first runStart along the longest, straightest wall. Roll the underlay out and cut it roughly to length with a sharp retractable knife against a straight edge, leaving a little extra to trim precisely later. Keep the blade retracted between cuts — a bare blade dragged across a floor is an easy way to nick your hand or the boards.
FU-07Butt and tape the joinsLay each following run tight against the last with no overlap and no gap — a gap or overlap will show as a ridge under the finished floor. Tape every join with the underlay's own jointing tape, or a general underlay tape if none was supplied, so the sheets don't shift while you fit the flooring.
FU-08Trim to the walls and leave an expansion gapTrim the underlay so it runs up to the skirting but doesn't need to bend up the wall — most underlays sit flat, not up the edges. Leave the usual 10-15mm expansion gap at the perimeter for the floating floor itself; this will be covered later by skirting or a scotia trim, so the gap doesn't need to look neat.
FU-09Do not fix the underlay downA floating floor underlay should sit loose under its own weight, held in place only by the tape between sheets and the flooring above it. Don't staple, nail or glue it to the timber boards — fixings through the underlay defeat the point of a floating floor and can telegraph through as bumps.
FU-10Tidy up and check the floor is readySweep up offcuts and tape scraps, and bag them for disposal. Walk the covered floor once more to check for any lumps, loose grit underneath, or gaps between sheets before you start laying the flooring on top.