Soundproof underlay buying guide

A soundproof underlay is basically resilient, shock-resistant material that is installed beneath flooring. This layer helps to absorb shocks in order to improve sound insulation through floors or even walls.

Acoustic underlays are highly recommended for floors in a flat or multi-storey house, and can help to reduce noise by about 20 dB.

In new builds, a maximum impact sound transmittance level of 62dB is set for floors and stairs. This covers things like footsteps, jumping and dropped objects.

A maximum impact sound transmittance also applies to conversion projects. However, a maximum level of 64 dB is allowed in this case.

A soundproof underlay is essential since it provides both thermal and acoustic insulation.

Before you go about installing an underlay, it is highly recommended to set up a vapour barrier. Made of plastic or foil, this layer helps to prevent moisture getting into the floor or insulation. This step is important for both new builds and retrofitted floors.

Some underlays come with a vapour barrier but most required the plastic film to be installed first. Your underlay will then be installed on top of this layer.

Cork

Cork is one of the most insulating materials. Used alone or in combination with rubber, cork provides the best acoustic insulation and shock absorption. Cork underlays come in boards or rolls and vary in thickness from about 2 to 8 mm. Your cork underlay must be either less thick than your flooring or the same thickness to avoid problems with your floor installation.

Rubber

Just like cork, rubber underlays offer high performance in terms of sound insulation. This material offers the best compression resistance thanks to its flexibility. It also offers a long service life. Rubber also comes in boards or rolls and varies in thickness from 2 to 10 mm.

Polyethylene foam

While it is the thinnest and easiest type of underlay to fit, foam is not the best option in terms of insulating properties or resistance. Polyethylene foam underlays usually come in rolls and measure about 2 mm in thickness.

Natural fibres

This type of underlay is better at thermal insulation than sound insulation. That said, while it is a slightly less popular option than other materials, it does offer pretty good insulation overall. It comes in boards of about 4 mm in thickness. As the name suggests, natural fibre underlay is made of natural wood fibres and is therefore fairly rigid. That's why it usually comes in boards rather than rolls.

Extruded polystyrene

Polystyrene underlay comes in boards measuring 5 mm in thickness. It is also possible to find thinner boards (around 1 to 3 mm) that come in folded up in a kind of accordion shape. Often combined with a thin layer of aluminium (or another material), extruded polystyrene is a pretty worthy ally in terms of soundproofing. It also offers good value for money.

Tile underlay is designed to lie between the subfloor and tiles. If you've converting a floor, the insulation should be placed between the old floor and the new tiles. Cork underlay or extruded polystyrene will usually work best in this case, but your choice will come down to the level of sound insulation you're hoping to achieve.

However, this type of installation does require some expertise as you will need to start with a very smooth and even surface before you lay your tiles.

Any type of underlay can be installed beneath a wooden floor so you just need to think of your own needs. If you are gluing down the flooring, go for a thin underlay.

If you are nailing your floor to your joists, you can place the underlay between the joists. The ideal option here will be polyurethane foam or glass wool.

When it comes to laminate floors, you'll have a wider choice of underlays. However, laminate flooring does require the most help with soundproofing.

As a reminder, you have to fit a vapour barrier before installing a floating hardwood or laminate floor.

Vinyl click floor tiles or boards do not require a vapour barrier as this type of flooring is designed to be watertight. In terms of underlay, choose a material that is resistant to footfall.

Vinyl boards, tiles or sheets are thin and flexible and, without a suitable underlay, may buckle under the weight of feet or furniture.

For PVC flooring, the best acoustic insulation will be provided by rubber.

Cork can also work as long as long as it is reinforced with rubber as cork alone is too soft.