Soundproofing Between Rooms: Complete Guide
A thermally perfect house can still be unliveable if you can hear the living room TV from the bedroom, or footsteps from the floor above while sitting on the sofa. Acoustic insulation between rooms is often treated too casually: a standard 13mm plasterboard partition goes up, resilient strips are forgotten, back-to-back electrical sockets are drilled in, and the problem is only discovered once the painting is done. Yet gaining 25 dB of sound reduction between two rooms does not cost a fortune if you know the right principles. This guide explains how sound works, which indices to target, and which technical solutions to apply room by room.
Understanding Noise Before Treating It
The classic mistake is trying to insulate without first identifying the nature of the noise. The solutions differ radically depending on the type of transmission.
The Three Families of Noise
- Airborne noise: voices, television, music, barking. It travels through the air and strikes surfaces. A good massive or decoupled partition stops it.
- Impact noise: footsteps, falling objects, chairs being dragged. It originates from direct contact with a surface, which vibrates and radiates sound into the adjacent room. Only mechanical decoupling (floating screed, resilient underlay) attenuates it.
- Equipment noise: MVHR, plumbing, toilet flush, heat pump. A mix of structure-borne vibrations and airborne noise. Treated with flexible fixings and absorbent materials.
Added to this is flanking transmission: sound that bypasses the partition by travelling through adjacent walls, the floor or the ceiling. An acoustic partition placed on a non-decoupled slab loses 10 to 15 dB compared to its theoretical potential.
Key Indices to Know
| Index | What it measures | Typical values |
|---|---|---|
| Rw (dB) | Airborne sound reduction of a partition in laboratory conditions | Standard 13mm board: 32 / Acoustic: 50-60 |
| DnT,A (dB) | Actual sound reduction measured on site (completed dwelling) | Target: 50-55 dB between rooms |
| L’nT,w (dB) | Impact noise perceived in the room below | Lower is better. Target: ≤ 58 dB |
| αw (0 to 1) | Absorption coefficient of a material (echoes) | Rock wool: 0.9. Tiles: 0.02 |
Tip: on the decibel scale, +10 dB of sound reduction = noise perceived as twice as quiet. Moving from Rw 32 to Rw 52 is not “20% better” - it is four times quieter to the ear. This justifies the price difference between a standard partition and an acoustic one.
The Physical Principle: Mass, Spring, Mass
The entire art of acoustic insulation comes down to three words: mass, spring, mass. A single-leaf partition, however heavy, vibrates like a drum. To break this vibration, two masses are layered, separated by a flexible element (wool, air gap) that absorbs the sound energy.
This is the fundamental difference between:
- a standard partition (1 board + frame + wool + 1 board): Rw ~ 32 dB
- an acoustic partition (2 boards + decoupled double frame + wool + air gap + 2 boards): Rw ~ 58 dB
At roughly the same thickness, the gain exceeds 25 dB. The secret is decoupling the two frames. If they share the same track, sound crosses the metal without encountering the spring. This is what is called a acoustic bridge (flanking path).
Warning: simply doubling the boards on a single frame only adds 4 to 6 dB. It is worthwhile, but far from the spectacular gain one might imagine. For a real quality leap, you need two independent frames or a high-density acoustic board (such as Knauf Diamant or Fermacell).
Partition Walls: The Solutions
Here are the main partition configurations between rooms, ranked from least to most effective.
Level 1: Standard 13mm Plasterboard Partition (Rw ~ 32 dB)
One 13mm board on each side of a 48 or 70mm stud frame, with 45mm glass wool. This is the minimum regulatory requirement for dwellings, but not sufficient to separate two bedrooms or a bedroom from the living room.
- Cost: £22-30/m² supplied and fitted
- Suitable for: circulation areas, wardrobe divisions, non-sensitive internal walls
Level 2: 13mm Board + Acoustic Board (Rw ~ 42 dB)
Same frame, but one of the two boards is replaced by a high-density acoustic board (Knauf Diamant, Fermacell). Real gain: 6 to 10 dB for a modest additional cost.
- Cost: £30-44/m²
- Suitable for: bedroom/landing separation, bedroom/bathroom
Level 3: Double Acoustic Cladding Partition (Rw ~ 48 dB)
Two acoustic boards on each side (4 boards total) on a 70 or 90mm frame, 70mm rock wool. A good thickness/performance trade-off.
- Cost: £48-66/m²
- Suitable for: bedroom/bedroom, bedroom/living room
Level 4: Decoupled Double-Frame Partition (Rw ~ 58-65 dB)
Two independent frames separated by a 10 to 30mm air gap, each clad with two acoustic boards, 100 to 140mm rock wool. This is the acoustic benchmark: a lively conversation is barely audible through it.
- Cost: £80-115/m²
- Suitable for: home cinema, studio, dwelling/commercial unit separation
| Solution | Thickness | Rw (dB) | Price/m² |
|---|---|---|---|
| Standard 13mm single 48mm frame | 7 cm | 32 | £22-30 |
| 13mm + acoustic board | 7 cm | 42 | £30-44 |
| Double acoustic 70mm frame | 10 cm | 48 | £48-66 |
| Decoupled double frame | 14-18 cm | 58-65 | £80-115 |
Best practice: with a tight budget, prioritise the sensitive partitions (bedroom/bedroom, bedroom/living room, bedroom/WC) at Level 3, and keep Level 1 for circulation areas. A proper treatment in 5 places is better than a poor one everywhere.
The Details That Make All the Difference
An acoustic partition can be ruined by five installation mistakes. All are avoidable if anticipated.
1. Resilient Strips Around the Perimeter
Before screwing the track to the floor and ceiling, glue a resilient strip (polyethylene foam or SBR strip, 3 to 6mm) under the track. It absorbs vibrations that would otherwise travel directly into the slab or upper floor. Without the strip, you lose 5 to 8 dB.
2. Perimeter Joint with Acoustic Sealant
All joints (floor, ceiling, side walls) must be treated with acoustic sealant (non-setting silicone). Air that passes through carries sound: a 1mm open joint halves the Rw.
3. Offset Electrical Back Boxes
A back-to-back socket on the other side of the partition creates a major acoustic weak point (loss of 8 to 12 dB). Solution: offset back boxes by at least 30 cm, and use airtight electrical back boxes (such as Schneider Multifix Air) with an integrated membrane.
4. Seal Service Penetrations
Cable and pipe passages (electrical, plumbing, MVHR) through the partition must be sealed with acoustic foam (PU foam, fire-rated) then rendered. An unsealed 50mm hole cancels the 30 dB of the partition in that area.
5. Continuous Insulation Fill
The insulation must fill the entire volume of the partition, without compression, without gaps at the top or bottom. Rigid slab insulation (semi-rigid rock wool) holds in place better than roll insulation in a vertical partition. Also remember to bring the insulation down to floor level, behind the skirting board.
Warning: do not confuse acoustic wool with standard thermal wool. A 100mm thermal glass wool delivers approximately 28 dB of absorption; the same thickness in acoustic rock wool delivers approximately 38 dB. On the same partition, that is 10 dB of difference for an extra cost of around £1.50/m². Favour rock wool or high-density acoustic glass wool.
Floors Between Storeys: The Number One Issue
The noise that causes the most problems in a house is impact noise at the ground floor ceiling: footsteps, toys dropping, chairs sliding. An untreated concrete slab transmits almost all of these shocks.
Solution 1: Resilient Underlay Under Timber or Laminate Flooring
An acoustic underlay of 3 to 5mm (cross-linked foam, wood fibre, cork) laid between the slab and the floor covering. Attenuation: 18 to 22 dB.
- Cost: £3.50-10/m²
- Suitable for: upper floors with floating timber or laminate
Solution 2: Floating Screed on Acoustic Insulation
The benchmark for new builds. A high-density acoustic insulation board (dedicated rock wool, 20 to 40mm) is laid on the slab, then a 50mm screed on top, with no contact with the walls (perimeter strip turned up at the edges). The floor covering (tiles, timber) is laid on top of the screed.
- Attenuation: 25 to 35 dB on impact noise
- Cost: £30-48/m² (insulation + screed)
Solution 3: Suspended Decoupled Ceiling
At the ground floor ceiling, a suspended ceiling on anti-vibration hangers (such as Vibrofix) is built, with 100mm rock wool and double acoustic board. Attenuation: 12 to 18 dB.
- Cost: £44-70/m²
- Suitable for: renovation, or as a complement to floating screed
Tip: in new builds, combine floating screed + decoupled suspended ceiling on upper floors above bedrooms. This is the investment that makes the most noticeable difference in daily life, especially with children. The additional cost (£35-55/m² extra) is negligible compared to the comfort gained.
Which Level to Target Room by Room
Not all partitions in a house require the same attention. Here is a prioritisation guide to calibrate the budget.
| Separation | Recommended level | Target Rw index |
|---|---|---|
| Bedroom / bedroom | Double acoustic 70mm frame | ≥ 48 dB |
| Bedroom / living room | Decoupled double frame | ≥ 55 dB |
| Bedroom / bathroom | Double acoustic + plumbing treatment | ≥ 50 dB |
| Bedroom / WC | Double acoustic + toilet cistern isolation | ≥ 50 dB |
| Living room / open kitchen | 13mm + acoustic board (or nothing if open plan) | 35-40 dB |
| Study / living area | Double acoustic 70mm frame | ≥ 48 dB |
| Utility room / living area | Double acoustic + rubber mounts under appliances | ≥ 45 dB |
| Garage / living area | Masonry wall + acoustic lining | ≥ 55 dB |
Decision Tree
Doors: The Weak Link
A partition rated at 50 dB is useless if the door only achieves 22 dB. A budget hollow-core door barely insulates better than a curtain. The options:
- Solid-core door (particleboard or solid MDF panel): Rw ~ 28 dB. Moderate additional cost.
- Acoustic door set (compressible perimeter seal + automatic threshold): Rw 32 to 38 dB.
- Studio door (double cladding, multiple seals, fitted threshold): Rw 38 to 45 dB. Essential for a music studio or soundproofed office.
The floor threshold is critical: a 5mm gap under the door loses 10 dB. An automatic drop-seal (Ellen Matic, Athmer) or a fitted threshold with seal are the effective solutions.
Equipment Noise: Do Not Forget the Plumbing
Tap and toilet flush noise in a bedroom adjacent to the bathroom is a classic source of regret. Three levers:
- Anti-vibration sleeves on pipe fixings (rubber, neoprene).
- Insulated boxing for soil and vent stacks (50mm rock wool + acoustic board).
- Silent wall-hung WC (concealed cistern frame with foam, such as Geberit Sigma) rather than a standard floor-mounted toilet.
For MVHR: fit a silencer on the supply/extract duct at the unit, and mount the unit on anti-vibration pads in an uninhabited space (loft, utility room).
Costs and Budget for a 100 m² House
Here is a realistic acoustic budget for a new build aiming for good comfort without extravagance.
| Item | Quantity | Unit price | Total |
|---|---|---|---|
| Resilient underlay under upper floor screed | 50 m² | £5/m² | £250 |
| Floating screed with acoustic insulation | 50 m² | £16/m² (self-build materials) | £800 |
| Level 3 acoustic partitions (double acoustic 70mm) | 60 m² | £19/m² | £1,140 |
| Acoustic boards replacing standard 13mm | 80 m² | £5/m² (surcharge) | £400 |
| Perimeter resilient strips | 200 m | £1.30/m | £260 |
| Acoustic sealant + airtight back boxes | lump sum | £220 | |
| Anti-vibration hangers for ceilings in critical areas | 30 m² | £7/m² | £210 |
| Total acoustic surcharge | approx. £3,280 |
For roughly £3,280 of additional materials on a £180,000 build, you transform the everyday experience of living in the house. This is one of the best cost-to-comfort ratios in the entire build.
Common Mistakes to Avoid
Checklist: before closing the partitions
- Resilient strips fitted under all tracks (floor and ceiling)
- Acoustic sealant around the perimeter of every acoustic partition
- Electrical back boxes offset by at least 30 cm on each side
- Membrane-sealed airtight back boxes on acoustic partitions
- Service penetrations sealed with acoustic foam
- High-density acoustic rock wool (not standard thermal wool)
- Insulation filling the full volume with no compression or gaps
- No standard 13mm boards on sensitive partitions (bedrooms, living room)
- Floating screed decoupled from walls (perimeter strip turned up)
- Soil and vent pipework with anti-vibration pipe clips
- Automatic drop-seal on bedroom doors
- MVHR on anti-vibration pads, silencer on ducts
- Ear test before closing up: knock with your fist, speak loudly, check the drop
Going Further
Acoustics must be addressed at the same time as the rest of the insulation, not as an afterthought. Some related articles:
- Choosing and fitting plasterboard as internal lining for board installation techniques.
- Understanding thermal bridges and how to avoid them: the continuity logic applies to acoustics as well.
- Insulating a ground floor: suspended floor or slab for complete floor treatment.
- Minimum acoustic requirements for new builds are detailed by the relevant building regulations - consult the Association of Noise Consultants for UK guidance.
- The Acoustic Glossary is a useful reference for technical terminology and acoustic indices.
- Certified Rw performance data for acoustic boards is available on the manufacturer’s website, for example Knauf or Fermacell.
Key Takeaways
Acoustic insulation between rooms is not simply about adding thick wool: it is a mass, spring, mass logic based on decoupling and continuity. A properly designed acoustic partition (double high-density cladding or decoupled double frame) costs £45-90/m² more than a standard partition, but transforms daily comfort. The details (resilient strips, sealant, offset sockets, sealed penetrations) matter as much as the choice of materials. In a new build, plan for acoustics from the drawing stage: it is ten times more effective and ten times cheaper than remediation during renovation.