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Noise - Environmental - Insulating the Home - Walls

Improving Walls

An external reference is to the proposed revisions to the Building Regulations which cover conversions and suitable sound insulation treatments to walls.

Firstly, it is worth inspecting the construction for weaknesses, such as spaces in the brickwork where joists are supported, 'thin' areas of a wall, where recessed fittings may be located, and transmission via the loft when there are very lightweight ceilings.

If the noise is coming from outside, the most likely weak points are air bricks, vents and the windows and these should all be considered; unless the walls are particularly lightweight, treatment of the walls to reduce external noise is unlikely to be beneficial.

The typical form of wall treatment is erecting a secondary leaf in front of, but isolated from, the existing wall; naturally the whole of the wall needs to be treated. A secondary construction might comprise

  • Make good any holes, gaps or cracks in the wall to be treated.
  • 2 layers of 12.5mm (or thicker) plasterboard arranged to have staggered and sealed joints, on a 75mm thick timber framework.
  • The timber frame should be supported from the floor, side walls and ceiling, but not the wall to be treated; the gap between two walls should be at least 125mm.
  • In the cavity, a 50mm thick (or thicker) quilt of mineral wool or glass fibre insulating material should be hung; note that this "insulation" is thermal insulation; actually this layer is "absorbing" sound as it passes through the cavity.
  • Ensure that a good seal is achieved between the plasterboard panels and the boundary walls, ceiling and floor, e.g. use acoustic non-hardening sealant, fit new skirting boards and coving.
  • Surface mount and fittings or services on the new inner wall; any holes will prejudice the performance.

Such a treatment will result in a significant loss of room area. An alternative would be to use plasterboard drylining (e.g. Crown dry-liner or Gyproc Triline) where the mineral wool backing, glued to the existing wall, isolates the new inner plasterboard layer; the same general advice as for secondary walls, should be followed; the cost and loss of area are likely to be lower, but so will be the likely improvement especially at low frequencies.

A possible alternative, in some circumstances, might be to build a floor to ceiling wardrobe across the whole wall to be treated, along the lines of the secondary wall construction above; note that the doors should be 50mm solid timber incorporating effective seals at the jambs and thresholds, i.e. louvered or sliding doors are not suitable. This way the cavity would be put to use and the clothes in the wardrobes would act as the absorbent material in place of the mineral wool.

Airbricks, ventilators & airconditioning units

The most cost effective form of noise control treatment is either to consult the manufacturer (if appropriate) for details of a proprietary silencer/attenuator, or to fit a mineral wool lined cowl or hood around the fan to direct air flow downwards, and prevent a direct sound path, through the fan unit to the room occupants. The cowling can be constructed of galvanised steel or plywood as appropriate; it should not fit too closely to avoid too great a load being placed on the unit.

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