Double-layer plasterboard partition: method, materials and checks

The basic build is the same as for any metal stud partition. U-shaped track runs along the floor and ceiling, vertical C-studs sit between them, mineral wool fills the cavity and both faces are boarded. In many systems these parts are called UW track and CW studs. With the double-layer version, however, two layers of board are screwed to each side, usually 12.5 mm thick. With a 75 mm stud the finished wall comes to roughly 125 mm, with a 100 mm stud roughly 150 mm.

Why two layers? Because the weight and stiffness of a wall directly affect how well it blocks sound, how it copes with knocks and how much it can carry. The second layer also covers the joints of the first, so the wall behaves as one piece and is less likely to crack along the joints.

A double-layer partition is the right choice especially when:

• You are separating a bedroom or child's room from the living room and quiet matters to you
• Kitchen units, wall cupboards, a television or heavier shelves will hang on the wall
• The wall is in a bathroom and will be tiled
• The wall is taller than usual, for example a gable wall in a loft or a room with a high ceiling
• The design calls for a certain fire resistance, for instance between a garage or plant room and the house
• The wall is in a hallway where prams, bikes or furniture are likely to bump into it

The NUMIQ price list also has a separate item for a single-layer plasterboard partition. Both are common and sound solutions, but each suits a different place. In plain terms:

• Boarding: the single-layer wall has one board on each side, the double-layer wall two. Per square metre that means twice the boards and screws, plus jointing of the first layer.
• Thickness: on the same stud the double-layer wall is about 25 mm thicker. In a narrow hallway or next to a door this sometimes matters.
• Sound: with mineral wool both reduce noise, but the double-layer wall does it noticeably better. You hear the difference most with voices and music.
• Strength: a single-layer wall sounds hollower when you knock and a board breaks through more easily on impact. A double-layer wall feels much closer to masonry.
• Loads: both carry light items. For heavy cupboards a single-layer wall almost always needs timber or steel backing. A double-layer wall has more reserve, but backing is still recommended for genuinely heavy items.
• Height: according to system manufacturers' tables, a double-layer wall allows a taller partition on the same stud.
• Time and weight: the double-layer wall usually takes noticeably longer and the material is heavier, which you feel when carrying it up several floors without a lift.

A single-layer partition makes sense for a walk-in wardrobe, a divider in a home office, a lining in a storeroom or anywhere you expect nothing special in terms of sound or load. If you are unsure about a bedroom or bathroom, in practice it is far harder to upgrade a wall later than to build it double-layered from the start.

Plasterboard does not like moisture or uneven surfaces. Check a few things before installation starts.

State of the building

• Wet trades, meaning plastering and screed, are finished and dry, otherwise the boards take up moisture and the joints crack later
• Windows are fitted and the building is weathertight, and in winter it is heated to roughly above 10 °C
• The floor and ceiling along the line of the wall are sound and reasonably level, with larger unevenness corrected beforehand

Decisions to make in advance

Once the second side is closed, you no longer have access to the inside of the wall. So be clear beforehand about:

• The exact position of the partition and doors, including the clear width and height of the opening and the type of door frame
• Where sockets, switches, lights and data cables will go
• Where the kitchen, television, washbasin, wall-hung WC or water heater will be, so that backing can be fitted
• Whether the partition will stand on the structural slab or on the finished screed

The last point matters for sound. If the partition stands on a floating floor that runs continuously underneath it from one room to the next, sound travels through the floor and the double boarding loses part of its effect. Where quiet really matters, the partition is fixed to the structural floor and the screed is broken along its line.

Flats, landlords and building regulations

In a flat, always agree the work with the building management or owners' association first. A lightweight partition does not touch the structure, but it changes the layout of the flat and the work creates noise and dust in shared areas. If you rent, you also need the landlord's consent. Whether your alteration needs approval or notification under local building regulations depends on where you live and what the wall does, so check with the local building authority rather than assuming it is a minor job. Fire-separating walls in particular must follow the approved design and the manufacturer's tested system.

Studs and track

Galvanised steel track and studs are used in widths of 50, 75 and 100 mm. For ordinary partitions in homes, 75 mm studs are the usual choice, as they leave a good cavity for insulation and cables. 50 mm studs suit places where every centimetre counts and the wall is not tall. 100 mm studs or doubled studs are used for tall walls or bulkier services. At door openings, heavier gauge door studs (often called UA profiles) are used instead of ordinary studs so that the door does not make the wall shake when it closes.

Boards

• Standard board (type A under EN 520, usually grey or ivory face paper): for dry rooms such as bedrooms, living rooms and hallways.
• Moisture-resistant board (type H, usually green): for bathrooms and kitchens. The board itself is not waterproofing, though. In the shower area and around the bath it needs a liquid waterproofing membrane with tape in the corners.
• Fire-resistant board (type F, usually pink or red): where the wall must resist fire. Fire resistance applies only to the complete system as tested by the manufacturer, meaning the specific studs, insulation, boards and screws together.
• Acoustic and high-density boards: heavier boards that improve sound insulation or impact strength and allow higher fixing loads. They suit bedrooms next to neighbours or home studios.

Layers can be combined, for example a standard board underneath and a moisture-resistant one on top. What matters is that the result matches what you expect from the wall.

Insulation and small materials

Mineral wool, either glass or stone wool, goes into the cavity, roughly as thick as the stud is wide. Sealing tape is stuck under the perimeter track so the steel does not touch the structure directly and pass sound into it. The first layer of board is usually fixed with screws about 25 mm long, the second layer with screws about 35 mm long so they pass through both boards and grip the stud securely. Joints in the face layer are filled with jointing compound and reinforcing tape, and external corners get corner bead.

1. Measure and mark the line of the partition on the floor, walls and ceiling, using a laser to transfer it vertically.
2. Stick sealing tape to the floor and ceiling track and to the end studs against the walls.
3. Fix the track to the floor and ceiling with plugs and screws, usually about every metre and with at least three fixings per length. Fix the end studs to the side walls.
4. Set the heavy door studs, fix them into both floor and ceiling and form a header above the opening.
5. Place the C-studs in the track, usually at 625 mm centres, all with the open side facing the same way. Under a concrete ceiling, cut the studs slightly short so the wall does not stop the ceiling from deflecting.
6. Screw the first layer of board to one side. Keep the boards about 10 mm above the floor so they do not draw up moisture.
7. Fit backing for heavy items: timber noggins or steel plates between the studs at the required height.
8. Run electrical cables through the holes in the studs and fit the back boxes. This part is done by an electrician.
9. Fill the whole cavity with mineral wool, leaving no gaps.
10. Screw the first layer to the second side, then the second layer to both sides. Offset the joints of the second layer from the first by at least one stud spacing, and horizontal joints by at least 400 mm.
11. Fill the joints of the first layer without tape, then tape and fill the joints of the second layer and sand them.

Why fill the joints of the first layer when nobody will ever see them? Open joints are paths for sound and, in a fire, for flames. System manufacturers require it, and anyone who skips it loses part of what the double-layer wall was paid for.

Surface finish level

The extent of jointing on the face layer is often agreed using finish levels Q1 to Q4. Basic jointing is enough under tiles, ordinary emulsion paint needs Q2, glossy paint or low side light from a window calls for Q3, and the most demanding finish is a full skim, Q4. Agree this in advance, otherwise expectations often differ at handover.

How demanding the job is, and therefore what it costs, depends on the conditions the crew finds on site.

• Straightforward: a straight wall at one height, no doors, level floor and ceiling, on the ground floor or with a lift, few services.
• More complicated: many door openings, sloping loft ceilings with lots of angled cuts, heights above a normal room so that scaffolding is needed, uneven old ceilings, connections to timber joists where movement must be allowed for.
• Slower: lots of backing, access panels, many electrical boxes, corners and returns, curves, a Q3 or Q4 finish.
• Logistics: twice the boards means twice the carrying. Up to a third floor without a lift, that is a lot of heavy work.

With a double-layer partition all of this multiplies, because every box cut-out, every door reveal and every corner is dealt with in four layers instead of two.

The drylining crew works in the middle of the build, so it helps to know the order:

• Before: bricklayers and plasterers, screed, and where relevant insulation and window fitting.
• During: the electrician, plumber and ventilation installer run their services after the first side is boarded and before the insulation goes in and the second side is closed. Agree an exact date so the crew does not stand waiting.
• After: tiler, decorator, flooring fitter and door installation.

Use back boxes designed for plasterboard with enough depth for double boarding. Do not place sockets on opposite sides of the wall directly back to back. Move them at least one stud bay apart, otherwise sound passes straight through. Electrical work must be done by a qualified electrician, and it is sensible to photograph the cable routes before the wall is closed.

In a bathroom, backing for a wall-hung WC, washbasin and taps is prepared together with the plumber. The waterproofing membrane goes on after jointing and before tiling.

• Joints of both layers in line: if the second layer is not offset, the wall is weaker along the joints and cracks appear there over time.
• Missing sealing tape: the wall rings at the edges and sound passes into the ceiling and walls. This cannot be fixed afterwards.
• Gaps in the insulation: wool that is fitted carelessly or squashed reduces sound insulation. You notice it mainly with voices.
• Overdriven screws: a screw that tears through the paper does not hold the board. Later you see popped screw heads or a board that moves.
• Wall jammed tight under the ceiling: if the studs hit the ceiling with no clearance, the wall takes load when the ceiling deflects and the top corner cracks.
• Boards touching the floor: when the floor is mopped or there is a leak, the board soaks up water.
• No movement joints: very long walls and junctions with different structures need movement joints as the manufacturer specifies, otherwise a crack forms in a random place.
• Fitting in a damp building: boards warp and joints crack once the heating goes on, often in the first winter.
• Forgotten backing: hanging heavy cupboards later on board and plugs alone leads to fixings pulling out and a damaged wall.

Building the frame and boarding a double-layer partition usually takes noticeably longer than a single-layer one, because each side is screwed twice. Allow for a break for the services between closing the first and second sides. Jointing compound dries according to the manufacturer, usually by the next day, longer in cool and damp weather. Higher finish levels mean several coats, so allow extra days. You can paint only once the compound is fully dry and a primer has been applied. Tiling waits until the waterproofing membrane has dried.

If you are handy, own a good spirit level or laser and have someone to help, you can build the partition yourself. Keep to dry rooms and lower walls with no fire requirements. Leave all electrical work to an electrician and do not touch anything structural.

1. Mark the line of the partition with a laser on the floor, ceiling and walls, and check for hidden pipes and cables along it.
2. Stick sealing tape to the track and fix it to the floor and ceiling with plugs and screws.
3. Set the C-studs at 625 mm centres, cut slightly shorter than the floor-to-ceiling height.
4. Screw the first layer of board to one side, leaving about a 10 mm gap at the floor.
5. Fit backing for shelves and cupboards, then have the electrician run the cables.
6. Fill the cavity with mineral wool without gaps, wearing gloves.
7. Screw the first layer to the second side, then the second layer on both sides with offset joints.
8. Fill the joints of both layers, using reinforcing tape on the face layer.
9. Sand, prime and let everything dry before painting.

Boards are heavy, so always lift them in pairs when fixing to the ceiling. Wear a dust mask and safety glasses when cutting and sanding.

Before the second side is closed, ask to see the insulation, backing and cables, and photograph them. When the work is done, check:

• Flatness of the wall with a 2 m straightedge in several directions, within the agreed finish level and the tolerance in the relevant national standard
• Plumb of the wall and the door reveals with a spirit level
• That the door opening has the agreed width and height and the studs do not flex
• That face-layer joints are smooth, without cracks or visible tape
• That screw heads are set just below the surface and filled, with no torn paper
• That external corners are straight and protected with bead
• That electrical boxes are firm and in the agreed positions
• That the wall does not sound hollow when knocked, which would suggest missing insulation or a missing layer
• That the gap at the floor and the joint at the ceiling are in place
• That you have photos of the backing, services and insulation taken before the wall was closed