Choosing Parquet Underlay: Sound Insulation and Moisture Barrier

Parquet underlay is a thin technical layer rolled out beneath laminate flooring that softens impact noise and blocks moisture rising from the subfloor. Three criteria decide the right product: vapour barrier capability, sound reduction value and compressive strength. With underfloor heating, low thermal resistance matters more than thickness.

What is parquet underlay and why is it essential?

Parquet underlay is a technical intermediate layer between the laminate boards and the screed that handles mechanical, acoustic and moisture duties at the same time.

Laminate parquet is installed as a floating system, meaning the panels are not glued to the screed but lock together to form one continuous surface. That floating structure needs balanced, uninterrupted support underneath. The underlay evens out millimetric level differences in the screed, so the locking joints are not stressed at a single point, and the risk of board edges opening over time drops considerably.

The second duty is acoustic. A hard laminate surface laid directly on screed transmits footsteps clearly to the flat below and produces a hollow ring inside the room. The underlay dampens that vibration. The third duty is moisture control. In reinforced concrete floors, capillary moisture can keep travelling upward for years. An HDF core panel swells under prolonged moisture and the locking profiles suffer irreversible damage. An underlay with an integrated vapour barrier cuts off that path. In She Parquet installations, the underlay is treated as seriously as the parquet itself.

Sound insulation: impact noise or in-room noise?

There are two distinct acoustic performances, and an underlay may be good at only one of them.

The first is impact sound reduction, which describes the footsteps, chair movements and heel clicks the neighbour below hears. Product labels usually express it as a reduction figure in decibels, and common underlays on the market declare values roughly between 18 and 22 dB. The second is in-room walking noise, the dull thud you hear in your own space while walking on the floor. In homes, this second type is usually the one that causes discomfort.

Rubber based and high density felt underlays perform strongly against impact noise. Thin foam based products offer an economical base but their acoustic contribution stays limited. In apartment buildings, and particularly in children's rooms and hallways with heavy circulation, prioritising acoustic performance makes sense. In hotel projects, in-room comfort and corridor insulation are assessed separately. Pattern choice also shapes perception, since across wide surfaces the aston louis plank laminate parquet series demands a flat and continuous base.

The vapour barrier and screed moisture

A vapour barrier is a thin polyethylene layer that stops moisture rising from the subfloor from reaching the HDF core of the laminate.

Common industry practice is that screed moisture must fall below 2 percent by weight before laminate is installed, and on cement screed with underfloor heating the threshold is kept even lower. A barrier, whether attached to the underlay or laid separately, is not a substitute for that measurement. Laid without testing, it simply traps the moisture and postpones the problem.

Polyethylene film around 0.20 mm thick is the usual choice. The critical detail is overlapping: strips must overlap by at least 20 centimetres and be joined with waterproof tape. At wall junctions the barrier is turned up to skirting height, with the excess trimmed once installation is complete. On ground floors, in basements and on slabs in contact with soil, the barrier is not optional but mandatory. Reading these criteria alongside the general logic explained in how laminate parquet selection should be made makes the decision much easier.

Underlay types and where each one belongs

Underlay selection follows the moisture load of the space, the floor level within the building and the expected acoustic comfort.

• EPE foam: Economical and light, usually 2 to 3 mm. Adequate on upper floors and in low traffic rooms.
• XPS board underlay: High compressive strength, very effective at levelling out screed variations. Common at 3 mm and above.
• Rubber based: The strongest group against impact noise, heavy and more costly. Preferred in hotel and office projects.
• Cork: Natural, dimensionally stable, balanced acoustic and thermal comfort. Requires a separate vapour barrier.
• Felt or combined underlays: Supplied with an integrated barrier film, which speeds up installation.

As a general rule, 2 to 3 mm is enough under laminate parquet. Soft layers of 5 mm and above strain the locking profiles and can cause edges to open. With small format, heavily jointed patterns such as aston louis herringbone laminate parquet, a firm and thin underlay is decidedly safer.

Step by step underlay installation

1. Sweep the screed and vacuum it until it is completely free of dust.
2. Measure screed moisture with a meter and confirm the value is below the 2 percent threshold.
3. Check levels with a 2 metre straightedge and fill any hollows with repair mortar.
4. Lay the vapour barrier with strips overlapping by 20 centimetres and tape the seams.
5. Lay the underlay edge to edge without overlapping, taping the joints.
6. Turn the barrier up at wall junctions to skirting height.
7. Advance the underlay section by section, in the direction of the boards, within the same day.
8. Fix an expansion gap of 8 to 10 millimetres around the perimeter using spacers.

Underlay choice with underfloor heating

On heated floors the thermal resistance of the underlay must be as low as possible.

Thermal resistance is expressed in m²K/W, and the industry expects the combined value of parquet plus underlay not to exceed roughly 0.15 m²K/W. Thick, soft foam underlays consume that budget on their own, heat never reaches the room, and the system runs constantly at high water temperature. For this reason, thin XPS or underlays engineered specifically for heat transfer are preferred.

The second critical point is surface temperature: the parquet surface should not exceed 27 degrees. Beyond that, dimensional movement and edge shrinkage appear in the panels. The commissioning protocol matters too. Once the screed has cured, the system is heated gradually and then cooled for a few days before installation. She Parquet teams build this protocol into the installation plan.

Common mistakes and long service life

The most frequent mistake is trying to solve an acoustic problem by making the underlay thicker.

On a soft, thick layer the panel flexes downward under foot, the locking teeth fatigue, and after a couple of seasons squeaking and edge separation begin. The second mistake is overlapping underlay strips, which creates a visible ridge across the surface. The third is laying the vapour barrier only on the floor and failing to turn it up at the walls.

Another widespread error is installing directly over old ceramic or PVC without filling the grout joints first. Ultimately, the underlay is the component that quietly extends the life of your floor. For product groups and pattern alternatives you can browse the laminate parquet articles section, and for the details of herringbone installations see herringbone laminate parquet, elegance and durability together.

Frequently Asked Questions

Can laminate parquet be installed without underlay?

It is not technically advisable, because the underlay acts both as a moisture barrier and as the balancing layer that protects the locking system. Without it, footstep noise increases noticeably and the joints fatigue early. Most manufacturers treat installation without underlay as grounds for voiding the warranty.

How many millimetres of underlay should I choose?

The common and safe range under laminate is 2 to 3 millimetres. Soft underlays of 5 millimetres and above can cause flexing beneath the panel, edge separation and squeaking. Rather than adding thickness, it is better to select a denser and firmer material.

Is a vapour barrier needed on every subfloor?

It is always required on concrete and screed subfloors, and it must never be skipped on ground floors, in basements or on slabs in contact with soil. On dry timber based subfloors a barrier can create condensation risk underneath, so it should be assessed with expert advice. A barrier never replaces a screed moisture measurement.

Which underlay suits underfloor heating?

Thin, dense underlays with low thermal resistance are preferred, and the combined resistance of parquet and underlay should not exceed roughly 0.15 m²K/W. Thick foam underlays trap heat and reduce system efficiency. The parquet surface temperature should also stay below 27 degrees.

Does underlay solve noise problems completely?

Underlay reduces impact noise significantly but does not deliver full insulation on its own. Slab thickness, screed type and skirting detailing all influence the result. The best outcome comes from combining a rubber or high density felt underlay with correct expansion detailing.