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We can hear the neighbours’ TV. How can we go about soundproofing?

We live in a semidetached house that is unsuitable for external wall pumping

'We can often hear the neighbour’s television, especially in the upstairs bedroom.' Photograph: iStock

Pat McGovern
Tue Apr 16 2024 - 05:45

Is it possible to pump internal walls as a means of soundproofing? We live in a semidetached house and can often hear the neighbour’s television, especially in the upstairs bedroom. The house is unsuitable for external wall pumping with many houses in the estate opting for external insulation. However, two houses have had the front facade of the house pumped.

Soundproofing an existing house is not an easy task and there are no fully successful solutions. Pumping the cavity is usually associated with thermal insulation and can be effective in that regard but has little impact on soundproofing.

There are two types of noise: airborne (muffled voices, TV or music from next door) and impact (vibration from footsteps, doors banging, a drum kit) and the methods of treatment differ.

Pat McGovern is a chartered building surveyor

In your case, the problem seems to be mostly airborne noise. The key to airborne soundproofing is to increase the “mass” of the wall, or in other words, increase its density.

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Before trying to solve or reduce the problem, you need to know the type of wall between your house and your neighbour’s. The standard is a solid party wall of brick or block formation – usually block – with a plasterboard dry lining. If the house is timber framed, the wall is usually a solid block wall, but it may be a double stud wall with no blockwork. Very rarely is a party wall of two-leaf block wall construction with a cavity. For this reason, pumping some kind of soundproofing material into the cavities is not possible.

In the case of your property, I will assume the party wall is a single block, 225mm thick laid on the flat (on its long edge), with a plasterboard dry lining and with no render finish in the attic. This is the standard, even today; however, as surveyors, we find that these walls can be poorly constructed with beds of mortar often roughly pointed and where the mortar only partially fills the gap between blocks. This is not good for soundproofing as sound passes through.

The solution:

  • A “simple” fix would be to repoint the party wall. You would check for any gaps or weak points in the wall pointing. If water can get through, sound can get through. You would then fill the gaps by repointing or using a proprietary acoustic sealant.
  • Adding a layer of sand cement render will greatly increase the mass and density of the wall.
  • Adding an insulated soundproof board will further improve the sound insulation of the wall and also improve its ability to absorb sound energy and vibration.
  • A particular weak point is the party wall in the roof space (attic). The joint between the roof covering and the top of the party wall should be checked and sealed. This is also an important fire seal in a compartment wall (a fire-resisting wall, delineating a compartment or part of the house).
  • Structural timbers built into a party wall can reduce its effectiveness while increasing the fire safety risk. The purlin support (a horizontal timber) to the rafters in the attic often rests on the party wall. Purlins should be sleeved to offer increased fire protection, and this will also reduce sound transfer.
  • Sockets and switches should not be fixed to a party wall and if they are you should consider relocating them. In the old days, the wall would have been chased to bury the cables and recess the socket or switch boxes, thereby reducing the thickness of the wall and in doing so its soundproofing qualities.

Doing all this in an existing house is not easy and involves stripping back all the current finishes and joinery details. What’s more, to be one hundred per cent efficient, you would need to do this on both sides of the party wall. It could be worth a chat with the neighbours because if you can hear their TV, they can hear yours, so soundproofing both sides may be mutually beneficial. Make that call.

Pat McGovern is a chartered building surveyor and a member of the Society of Chartered Surveyors Ireland

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