Sound Insulation in Drywall Partitions: Rw Values and Build-ups
The acoustic performance of a drywall partition is set by the build-up, not the brand of board. With the same materials you can produce 35 dB or 58 dB. Three things make the difference: how many layers of board, what goes inside, and how the frame is built.
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What Rw means in practice
Rw is the weighted sound reduction index — a single number describing how much a building element cuts sound. Higher is better.
In everyday terms: at 35 dB, speech next door is audible and largely intelligible. At 45 dB you hear speech but cannot make out words. Above 50 dB normal conversation is effectively inaudible and a television drops to a murmur.
Between a bedroom and a living room the usual target is 45–50 dB. For a rental unit, a meeting room or a music room, the conversation starts at 52 dB.
Build-ups and typical values
The figures below are typical laboratory ranges. Site workmanship can pull them 3–5 dB lower.
| Build-up | Total thickness | Approx. Rw |
|---|---|---|
| Single frame, single board, no infill | ~75 mm | 33–36 dB |
| Single frame, single board, mineral wool | ~75 mm | 41–44 dB |
| Single frame, double board, mineral wool | ~100 mm | 47–50 dB |
| Twin independent frames, double board, wool | ~155 mm | 55–60 dB |
| Double board + high-density acoustic board | ~125 mm | 52–56 dB |
Infill: stone wool, glass wool, or none?
An empty partition behaves like a drum: the air cavity between the two boards couples sound straight through. Filling it with fibrous insulation breaks that resonance and is worth 6–8 dB on its own.
Acoustically the difference between stone wool and glass wool is small; the real difference is fire behaviour. Stone wool is class A1 and holds its form at high temperature, which is why it is preferred where the partition carries a fire requirement.
The infill has to fill the cavity completely. Insulation left short or slumped costs you performance in proportion to the gap above it.
Details that undo the insulation
Even a correctly built wall can be wiped out by one of the details below. Most of the problems we are called to look at start here.
- Back-to-back sockets: cutting boxes into the same stud bay from both sides leaves a direct hole through the wall. Offset them.
- Perimeter joints: without acoustic tape between the track and the floor or slab, sound passes along that line.
- Flanking over the ceiling: if the partition stops under a suspended ceiling, sound travels through the void into the next room. The wall must run to the structural slab.
- The door: hang a standard internal door in a 50 dB wall and the assembly performs like the door. The weakest element always governs.
- Rigid contact: if the two frames touch each other or share a track, vibration passes straight across; the point of a twin frame is that it is separated.
Choosing the right target
Not every wall needs 55 dB — cost and thickness climb quickly. Setting the target by use is the sensible approach.
| Use | Suggested target | Typical build-up |
|---|---|---|
| Splitting a room (same household) | 40–44 dB | Single frame, single board, wool |
| Bedroom / living room | 45–50 dB | Single frame, double board, wool |
| Meeting room | 48–52 dB | Double board + acoustic tape + full height |
| Separating rental units | 55+ dB | Twin independent frames |
| Music / studio | 58+ dB | Twin frames + high-mass board + door detail |
In short
- Rw comes from layer count, infill and frame design — not the brand on the board.
- Filling an empty partition with mineral wool is worth 6–8 dB by itself.
- Back-to-back sockets, untaped perimeters and flanking over a suspended ceiling are the three commonest faults.
- A wall can never perform better than the door in it.
- 45–50 dB is a realistic residential target; 55+ requires twin independent frames.
