Underlay
Underlay is the thin layer between your subfloor and a floating floor, and the right flooring underlay makes more difference to how a new floor feels, sounds and lasts than almost anything else. It smooths out small bumps, takes the hard edge off footsteps, cuts noise to the room below, adds a little warmth and, on concrete, keeps rising damp away from the floor.
The right underlay depends on the floor above it. Click wood and laminate floors use engineered wood flooring underlay and laminate flooring underlay: foam underlay for value, fibreboard underlay to level small dips and deaden sound, and acoustic underlay for flats and upstairs rooms. Luxury vinyl needs a thin, firm LVT underlay, never a thick, soft one.
On concrete, choose an underlay with a built-in damp proof membrane, and over underfloor heating, an underlay with a low TOG rating so the heat gets through. Our underlay guide explains each type in more detail.
Not sure what you need? Call our team on 020 3287 6206 and we will help you match accessories to your floor, or read our flooring accessories guide.
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What underlay does
A floating floor is not fixed to the subfloor; it rests on the underlay. The underlay spreads the load, bridges tiny bumps and gaps that would otherwise make boards rock or creak, cushions footsteps, reduces the sound that travels into the room below and the hollow sound in the room itself, and adds a little insulation. Some underlays also include a damp proof membrane. Glued-down floors and most nailed floors do not use an underlay.
How to choose underlay
Match it to your floor
Laminate and click engineered wood: foam, foam with a foil or film layer, fibreboard or rubber-based acoustic underlay, usually 2mm to 5mm thick. Luxury vinyl and SPC: a thin, dense underlay made for vinyl, usually 1mm to 1.5mm, unless the planks already have one attached; a thick, soft underlay lets the click joints flex and break. Floors with underlay attached: no second underlay, though a damp proof membrane may still be needed on concrete.
Match it to your subfloor
Concrete or screed: an underlay with an integrated damp proof membrane, or a separate membrane underneath, because concrete can release moisture for years. Floorboards or plywood: a breathable underlay, often fibreboard, which also smooths the lines of old boards; no damp proof membrane is needed on a timber subfloor.
Match it to the room
Flats and upstairs rooms: acoustic underlay reduces impact noise to the neighbours or the room below; check your lease, as many flats require a minimum sound rating. Underfloor heating: a low-TOG underlay approved for heating, so heat passes through easily. Cold rooms over unheated spaces: a higher-TOG underlay adds warmth.
Thickness: thicker is not always better
A thicker underlay feels softer, but too much give lets click joints flex and can break them. Keep within the thickness the floor maker allows (often no more than 3mm to 5mm for laminate and wood, and around 1mm to 1.5mm for vinyl). If the subfloor is uneven, fix it with a levelling compound rather than relying on a thick underlay.
TOG ratings and underfloor heating
TOG measures how well a material resists heat. A low TOG lets underfloor heating warm the room efficiently; a high TOG keeps warmth in a room over an unheated space. For underfloor heating, the underlay and floor together should stay within the heating system’s limit, so choose an underlay sold for underfloor heating.
Laying underlay
- Clean the subfloor and remove any old underlay, nails and staples.
- On concrete, lay the damp proof membrane first (unless it is built in), overlapping joins by about 200mm and taping them, and turning it up the wall a little.
- Roll out the underlay in the same direction the floor will run, edges butted, not overlapped, and tape the joins.
- Lay the floor straight away so the underlay is not damaged by foot traffic.
Our installation guides show where underlay fits in each type of floor.
Common underlay mistakes
- A soft, thick laminate underlay under vinyl, which breaks the click joints.
- A second underlay under boards that already have one attached.
- No damp proof membrane on concrete.
- Overlapping the underlay joins, which leaves ridges under the floor.
FAQs on Underlay
Yes for floating floors such as click laminate, click engineered wood and click vinyl, unless the boards have underlay attached. Glued-down floors do not use underlay.
Follow the printed side or arrow on the underlay. Underlays with a built-in damp proof membrane usually have the film side down towards the concrete, with an overlap strip to tape the joins.
No. Carpet underlay is far too soft and thick: the floor would flex, the joints would break and the floor would feel spongy.
Not always. Too much softness lets click joints flex. Stay within the thickness the floor maker allows and level an uneven subfloor rather than relying on thick underlay.
No. Timber subfloors need to breathe, so use a breathable underlay without a membrane. Damp proof membranes are for concrete and screed.
An acoustic underlay with a good impact sound rating. Many leases set a minimum standard, so check yours before you buy.
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