Although many old houses are built more solidly than modern ones, when a house is divided into flats noise can still pass from outside and between flats. This is a guide to sound-proofing in period houses.
Airborne noise it literally carried in the air. Structural noise is passed in the structure of the building; the walls and timbers.
Although you are unlikely to have an airport, road or even slightly noisy neighbour moved, you may be able to stop the noise reaching your building. Sound can be reflected with solid structures such as walls, or absorbed by soft structures such as dense planting.
To block airborne noise you must seal up doors, windows and other gaps in the same way as you stop draughts. However this can cause problems with condensation. Try to open windows as often as you can.
Some of the sound will be re-emitted into the air by the walls and windows. This can be reduced by double-glazing windows. Conventional sealed units have a limited effect on noise; a larger gap achieved with secondary glazing is more effective and can be more attractive in period houses as original windows are easier to retain. With walls, a false wall should be built; battens are fixed to the wall, the gaps filled with insulation and then dry-lined with one or two layers of plasterboard.
Structural noise is more difficult to stop.
Vertical noise can be blocked with false floors and ceilings, disconnected as far as possible from the adjacent flat. For example the new joists must not touch the original ones. A typical overall thickness of a suspended ceiling system with insulation would be between 150-200mm. The new suspended ceiling should have a 50mm air gap between the floor above and the insulation below. Use a thick (100mm minimum) layer of sound insulation, packed tight with no gaps, of two 50mm layers at right-angles. All gaps around the edges of the room should be sealed with a sound-insulating mastic sealant. The supporting framework for the ceiling can be either timber or metal, but substantial enough to take the weight of the insulation. The fixings used to the support the suspended ceiling framework should also be able to absorb sound transmission. Use a plaster coving to ensure a good seal.
Structural noise through walls can only really be stopped by building a false wall, again not touching the original wall. Use a steel frame with acoustic quilt insulation and two layers of acoustic plasterboard with a skim coat of plaster. Some noise reduction can be achieved more cheaply by dry lining the walls with plasterboard, or at greater cost using acoustic plasterboard or else acoustic board with an acoustic insulation backing.
Once sound has got into your rooms, you can absorb it with furnishings. A carpet will be better than a hard floor. However, these approaches also absorb your own noise and mean that the relative volume of your neighbour's noise will be the same. It may be better to drown it out with your own noise by avoiding too many effective sound absorbing materials.