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What the Homeowners Were Dealing With
If you are trying to figure out how to soundproof a party wall in a semi-detached house, this is a real case study of exactly that. A 1960s UK semi where the owners were hearing everything from next door. Clear conversation, doors banging, kids running around, and worst of all, the neighbour’s washing machine vibrating through the floor and into every room in the house.
The noise was so constant they could follow the neighbours’ board game from their own living room. This is exactly the kind of situation a full party wall soundproofing installation is built to fix.
The Four-Step Soundproofing Method
Every step of Quietco’s 4-step soundproofing method was followed on this project.
Before anything gets soundproofed, every noise path has the same consistent process applied:
- A. Find and seal holes in the structure where noise pours in
- B. Open hidden voids in the floor and ceiling where noise travels and amplifies
- C. Sound-deaden vibrating surfaces with visco-elastic membranes
- D. Add isolation and mass using decoupled floating frames and various acoustic boards
This is why foam panels and clip-and-channel systems so often disappoint. They skip straight to step D without addressing what is happening behind the walls. The biggest gains in this project came from steps A and B, before a single acoustic board went up.
Find out more about our tried and tested, award winning method here
Why Treating Just the Party Wall Is Not Enough
Most people assume the party wall is the problem. It is one of the problems, but far from the only one.
Noise travels through your home in several ways:
- Through the suspended floor void beneath your feet
- Through the ceiling void above your head
- Along RSJ steel beams
- Through the chimney stack and fireback
- Through flanking walls running perpendicular to the party wall
If you only treat the painted surface of the party wall and leave everything else alone, you will still hear your neighbours. The best result you can realistically expect is a 30 to 50% reduction. That sounds promising at first, but even a small amount of residual noise is enough to keep you feeling unsettled in your own home.
The Two Root Causes to Fix First
Before any soundproofing layers go in, two structural problems need to be dealt with. Skipping these makes everything else pointless.
Holes in the Party Wall Structure
Above the ceiling plasterboard and below the floorboards, there were numerous small holes where joists met the party wall and where old services had passed through. Lots of small holes add up to one big hole. Until you brick these up and seal them with acoustic sealant, noise will keep pouring through regardless of what else you do.
The Suspended Floor Void Acting as an Amplifier
The hollow space beneath the floorboards acts like a drum. Sound from the neighbours enters the structure, resonates inside that void, amplifies, and radiates back up into the room. This is why so many people still hear noise after treating only the wall, as the floor void is working against them the whole time.
As a result, clearing the void, addressing damp, and disconnecting the joists from the party wall is non-negotiable for a real result. It is also why the washing machine vibration was felt so strongly. Those timber joists were a direct physical bridge between the neighbour’s appliance and this family’s floor.
How Every Noise Path in This Semi-Detached Was Treated
Party Wall
Sound deadened with 20mm rubber, then one of our trademarked wall systems was applied including a decoupled floating frame filled with Rockwool, resilient bars, and acoustic plasterboard.
One of the most important parts of this stage is what Jim calls “tuck it up and tuck it down.” The wall system does not stop at the skirting board or the ceiling line. It gets tucked all the way down into the suspended floor void to the subfloor, and all the way up into the ceiling void above. This seals the system off completely so noise cannot bypass the wall by sneaking through the voids above and below. This tucking process is where most of the physical labour sits and why a proper installation takes weeks, not a weekend.
Suspended Floor and Ceiling
The team disconnected the joists from the party wall and bricked up the holes. They then insulated the ceiling void with 200mm of Rockwool and overboarded the full ceiling with acoustic plasterboard. More on ceiling soundproofing here.
Chimney Stack and Fireback
The fireback is one of the most commonly skipped areas and one of the most important. The flue runs between floors, giving sound a clear channel between upstairs and downstairs rooms. Consequently, every layer applied to the alcoves was also applied to the fireback, with additional materials on top.
RSJ Steel Beams
Steel transmits sound easily. The team wrapped both RSJs in a viscoelastic membrane and insulated the web of each beam with Rockwool before installing the surrounding wall systems.
Upstairs Partition Wall
A hollow paramount board wall upstairs was resonating with the neighbours’ TV and sending sound back down into the lounge below. The team opened it up, insulated it fully, and closed it off.
Acoustic Secondary Glazing
Acoustic secondary glazing was fitted to the bay window. This reduces external noise coming in through the glass and also stops sound travelling between neighbouring bay windows, which is a commonly overlooked noise path in semi-detached homes.
Soft Furnishings and Room Acoustics
Once all the hard surfaces from the soundproofing work are in place, the room can sound echoey without soft furnishings to absorb that energy. The homeowners had a thick high-pile carpet fitted, which made an immediate difference. Curtains, blinds, and soft wall art all help too. These are not optional extras. They are the final step that makes the room feel genuinely comfortable to live in again.
For a full picture of what goes into a professional installation, Quietco’s solutions pages are a good starting point, or you can book a free noise diagnosis call to talk through your specific situation.
The Results
Watch the full video walkthrough of this project below:
Four weeks after the installation, here is what the homeowners reported:
- No more overheard conversations or words made out through the wall
- No more doors banging or children heard playing ball indoors next door
- Washing machine vibration completely gone from the lounge and all downstairs rooms
- Full privacy restored. They could talk and laugh normally without worrying about being overheard
Some very faint thumping from upstairs is still noticeable in complete silence, but the homeowners described it as distant, more like something outside than next door. With anything on in the background, it is a non-issue.
Overall, the transformation was significant. This lines up with what acoustic science tells us: every 10 dB reduction is perceived as roughly half as loud, which explains just how different a properly treated room feels compared to one with a surface-level fix.
If you are at the point of deciding what to do next, get in touch with Quietco to find out what the right solution looks like for your home.
FAQ
Can I just soundproof the party wall and skip the floor?
You can, but expect limited results. Treating only the party wall typically delivers a 30 to 50% noise reduction. To get a meaningful and lasting result, the floor void and ceiling void both need attention alongside the wall.
Do I need planning permission?
Not for soundproofing generally, but joist disconnection does require a building regulation application in the UK. Your local building control officer needs to inspect before work starts. Quietco handles this process as part of their installations.
How long does a full installation take?
A project like this one takes several weeks. Opening voids, disconnecting joists, and building properly decoupled systems is substantial work that you cannot rush without compromising the outcome.
Will I still hear anything after soundproofing?
Most airborne noise including conversation, TV, and music will be eliminated or reduced to an unnoticeable level. Some heavy impact noise like footsteps directly above may still be faintly audible in total silence, but significantly less than before.
