Short answer: there is no single best underlay for everything. On tiles or a cement screed, the underlay must have a damp-proof barrier; if noise is a concern, a higher-density acoustic underlay; and if there is underfloor heating, a specific underlay that lets the heat through. In every case, use the one recommended by the manufacturer of the laminate flooring: many guarantees depend on using a compatible underlay.
What underlay is for
Laminate is installed as a floating floor, on a thin layer between the existing floor and the planks. That underlay:
- Absorbs small irregularities in the subfloor.
- Protects the laminate from damp rising from the floor, if it has a barrier.
- Reduces footstep noise and the hollow sound.
- Adds some comfort underfoot.
It is not meant for levelling a floor with large differences in height: that must be corrected beforehand with levelling compound.
Types of underlay for laminate flooring
| Type | What it's good for | Bear in mind |
|---|---|---|
| Polyethylene foam | The cheapest and most common in dry areas | Without a damp-proof barrier, it is not suitable on cement or tiles on ground floors |
| Foam with damp-proof barrier | On tiles, cement screed and ground floors | The barrier must be overlapped and sealed at the joins to work |
| High-density acoustic underlays (boards, wood fibre, cork) | Flats with neighbours below or rooms where echo is a nuisance | More expensive; some have no barrier and need a separate membrane |
| Underlays for underfloor heating | Homes with underfloor heating or cooling | They must let the heat through: the manufacturer limits their thermal resistance |
How to choose for your situation
On tiles or cement screed
Cement and tiles can transmit moisture, especially on ground floors and in houses near the sea. Here the underlay must have a damp-proof barrier. It is what we use in our installations, including on ground floors, and we check the floor's moisture level beforehand during the visit.
On an old wooden floor
If you are laying laminate over parquet or wooden floorboards that are firm, manufacturers usually recommend not using a vapour barrier, so as not to trap moisture in the wood underneath. Check the data sheet for your laminate.
If noise is the problem
There are two different kinds of noise:
- Impact noise: what the neighbours below hear when you walk. A good-density acoustic underlay reduces it.
- Reflected noise: the hollow sound and echo in your own room. High-density underlays and some laminates with a built-in acoustic underlay reduce it.
Technical data sheets usually give a figure for each. If noise matters to you, compare those figures, not just the thickness.
With underfloor heating
Don't confuse the laminate underlay with the insulation of the underfloor heating system itself (the boards that go under the pipes, already installed during the build). On top of the heating, the laminate underlay must be thin and specific so that the heat reaches the room. More detail in the best floating floor for underfloor heating.
Common underlay mistakes
- Choosing the thickest one thinking it's the best: an underlay that is too soft or thick makes the click joints flex underfoot, and the floor ends up creaking or the joints open (see how to fix a creaking floating floor).
- Laying two underlays on top of each other: same problem.
- Overlapping the foam: foam strips are butted together; what is overlapped and sealed is the damp-proof barrier.
- Using the underlay to hide uneven floors: unevenness is corrected beforehand, in the subfloor.
Frequently asked questions
Do you have to put underlay under laminate flooring?
Yes, unless the laminate already has one built in. Without underlay, the click joints work against a hard, uneven floor and the laminate is noisier and wears out sooner.
Which underlay is best for damp?
One with a damp-proof barrier, properly overlapped and sealed. But no underlay solves damp in the subfloor: if the floor is damp, the cause must be found and fixed before installation.
Is the underlay built into the laminate enough?
It depends on the model and the situation. Some manufacturers require a separate damp-proof barrier on cement; the technical data sheet will tell you.