Sound insulation
of a wall.

Before talking about materials, you need to name the noise. Airborne noise is born in the air: voices, television, music, barking. It makes the partition vibrate, and the partition radiates it on the other side. Impact noise is born from a shock to the structure: footsteps, a chair dragged, a slammed door. It travels through floors and walls much further than the room where it started. Equipment noise, finally, comes from water falling in a duct, a fan, a boiler. A lining treats the first well, the second poorly, and the third not at all if the pipe remains rigidly fixed to the wall.

Next, you need to find the path. Sound goes through the wall itself, but it also passes through leaks: an electrical socket placed back to back with the neighbour's, an open service duct, a cracked joint at the foot of the wall, a shutter box. Finally, it goes around the wall through flanking transmission: the floor, the ceiling and the facade walls that run continuously from one home to the next. In an old building in Chambéry or Aix-les-Bains with timber floors, these indirect paths often weigh as much as the party wall.

That is why we start by listening on site, room by room, before proposing a partition. A sound insulation quote drawn up without knowing where the noise passes promises a result that nobody can deliver.

A wall stops noise better when it is heavy, and much better when it is made of two heavy leaves separated by a soft cushion. This is the mass-spring-mass principle: the existing wall is the first mass, the wool in the cavity acts as the spring, the plasterboard is the second mass. The sound that makes the first leaf vibrate is damped in the cavity instead of being transmitted directly to the second.

In practice, this gives a lining wall on a metal frame:

1. A frame independent of the wall. The tracks are fixed to the floor and the ceiling, and the studs do not touch the masonry, or are connected to it by anti-vibration supports. A frame screwed rigidly into the wall transmits vibrations and ruins a good part of the gain.

2. A fibrous insulation in the cavity. Glass wool, rock wool or plant fibre: their fibres slow the vibrating air. Our comparison of glass wool or rock wool points out that Isover announces, for its Optima lining system filled with GR 32, a gain of 12 to 26 dB compared with the bare wall: a figure that applies to the complete system, not to the wool alone.

3. One or two layers of plasterboard. The mass of the second leaf matters: double boarding, or a high-density board known as “acoustic”, improves the result where the stakes are high.

4. Flexible, airtight junctions. A resilient strip under the tracks, an acoustic seal around the perimeter, airtight and offset electrical boxes, no pipe rigidly fixed through it. A hole of a few square centimetres lets through a surprising share of the noise: airtightness to air and airtightness to sound go together.

Foams and decorative panels. They absorb sound in the room and reduce echo: very useful in a meeting room, a tiled office or a music studio. But they are light and porous: the sound that passes through the wall goes through them almost without loss. They correct a room's acoustics; they do not insulate from one room to another.

Thin insulation and “insulating” paints. A few millimetres bring neither mass nor spring. Our guide on insulating walls from the inside already details their thermal limits; they are the same when facing noise.

Bonded linings with rigid insulation. A board bonded directly to a polystyrene panel, itself bonded to the wall, forms a stiff system: at certain frequencies, it can transmit noise instead of damping it. It is a thermal solution, not an acoustic one. On our sites, this bonded lining remains very much a minority.

Treating the wall and forgetting the door. Between a bedroom and a living room, a hollow-core door with a gap of several millimetres under the leaf lets through more noise than the most careful partition. The gain is played out across the whole partition, door included.

The party wall of an apartment or a town house. This is the most frequent request. The decoupled lining wall is built on the side of your home, along the whole length of the wall and from floor to ceiling, redoing the sockets and skirting boards. It clearly improves insulation from the neighbour's airborne noise. It does not remove what passes through the shared floor and ceiling: in a building with timber floors, the result also depends on these junctions. In a co-ownership building, the rules may govern the works, and may require an acoustic underlay when a floor covering is changed: to be checked before the work begins.

The partition between two rooms. Between two bedrooms, our quotes most often provide for a 72/48 partition filled with wool between the studs: a 48 mm frame, a 13 mm board on each face. When the stakes are higher, bedroom against living room, home office, child's bedroom against master suite, we work on the number of boards and the type of frame, up to an independent double frame. This double partition, which we rarely price, is decided on a visit rather than on a price per square metre.

The ceiling and footstep noise. The upstairs neighbour's footsteps are impact noise: the real answer lies in their home, with a floor laid on a resilient underlay. From your home, a false ceiling suspended on anti-vibration hangers, with wool in the ceiling void and flexible junctions with the walls, clearly reduces airborne noise and partly reduces footstep noise. Our page on the price of a false ceiling per m² gives our ranges for these works.

Street noise. Facing a road or a railway line, the masonry wall is rarely the weak link: it is the windows, the air vents and the shutter boxes. Acoustic laminated or asymmetric glazing, properly sealed joinery and acoustic air vents do more than a lining. Our guide on window replacement starts there.

The order of 30 June 1999 on the acoustic characteristics of residential buildings sets the requirements for dwellings whose building permit application was filed from 1^st January 2000. It covers only new buildings, but it gives a useful order of magnitude of what “correct” insulation is.

For impact noise, the same order limits to 58 dB the level perceived in a main room when the floor of another dwelling is struck. An old building, built well before these rules, is often far from these values between two apartments: that is precisely where a well-designed lining wall brings the most.

The ranges below come from our 2024-2026 quotes in Savoie and Haute-Savoie, published on our page on the price of plasterboard per m². They are exclusive of VAT, with supply and installation by our plastering teams included.

Worked example. A party wall 4 m long by 2.50 m high is 10 m². Lined with insulation, it comes, according to these ranges, to €750 to €900 excl. VAT, i.e. €825 to €990 incl. VAT at the 10% rate, excluding painting and excluding reworking the electrics. An acoustic board or double boarding is added as an extra.

VAT. In a home completed more than two years ago, partitions and plastering fall under 10% VAT. A lining that thermally insulates a wall facing the outside may qualify for the 5.5% rate if it meets the technical criteria for energy renovation; a purely acoustic lining on a party wall stays at 10%. Our guide on VAT on renovation works details the cases.