Terraced or semi-detached houses can sometimes suffer from a lot of sound being transmitted through the party walls, even if the neighbours are not particularly noisy (some houses are just badly insulated). There are several ways to insulate a party wall to cut the sound that is transmitted, but one of the most effective is adding an insulated dry lining.
If the wall or walls to line feature a chimney breast, you need to decide if you want to lose 100mm in front of it or simply apply the lining in the alcoves on either side. In most cases, just lining the alcoves will cut out most of the transmitted noise, with the additional brickwork in the chimney breast acting as some sort of sound insulation. If the fireplace on the chimney breast in question is not used, you could consider bricking it up and plastering over it to increase the insulation. Although if you have a nice fireplace, even one which isn’t used, it is usually a nice focal point to a room.
Fixing the Head Plate
Measure out 100mm from the party wall you wish to line and mark this on the ceiling. Using 75mm x 50mm softwood, cut a length to the width of the room. Position the front edge of this piece of wood on the ceiling mark and nail it to the ceiling joists above. To find the joists, tap the ceiling until you hear a solid thud and then investigate further by pushing a thin nail or piece of metal through the ceiling plaster to see if you hit wood. Once you find one joist you should be able to easily find the rest as they are usually set at 400mm centers. Make any investigation holes in the area that will be covered by the head plate or hidden behind the lining.
Fixing the Sole Plate
Using a plumb line, transfer the position of the head plate onto the floor and cut yourself a Sole Plate using the same size timber as the head plate. Fix the sole plate to the floor using nails or screws (masonry nails if you have a concrete floor). Take your measurements carefully and make sure that the sole plate is perfectly in line with the head plate before fixing it down.
Adding the Studs
Measure the distance between the head plate and the sole plate at one end of the wall and cut a stud to fit between them. Use the same size timber as you used for the head and sole plate. Fix this first stud into place at the end of the sole and head plate, using a level to keep it vertical rather than relying on the wall. No repeat this process at the other end of the run. Now measure and fit studs all the way along the run at 600mm centres, using skew nailing to fix them in place. Have a look at our guide to skew nailing if you are unsure. You can cut and fix noggins between the upright studs to give the structure more strength if you want.
Adding the Insulation
You can now start to add the insulation material, either hanging sheets of mineral wool between the studs (nail or staple it to the studs to hold it in position) or cut and fit thick sheets of polystyrene insulation material between each stud. The tighter the fit, the better the sound insulation will be. The second part of the insulation will be the plasterboard. Cut a sheet to length and, starting at one end, attach this to the studs. Repeat this until the full run is covered. You can then add a second layer of plasterboard over the first, staggering the joints, to really add some soundproofing. Tape and fill the joints in the plasterboard and seal around the edges of the lining with non-setting mastic.
To finish off you can either skim the wall with plaster or simply decorate directly onto the plasterboard. Remember to add a new skirting board along the bottom, profiled to fit against the skirting at each end of the new wall. You can get more tips on finishing off a plasterboard wall here.