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Good results depend on understanding how the sound gets through. Noise travels through the air and through the structure, and it slips around walls by way of gaps, ducts, outlets and floor joists. A soundproofing contractor combines a handful of principles, adding mass, separating the two sides of an assembly, damping vibration, absorbing sound inside cavities and sealing leaks, to suit the noise, the building and the space you can give up.
This page covers airborne and impact noise, those principles, common projects, STC and IIC ratings, condo and fire-separation rules, and realistic expectations.
Airborne vs impact noise: which kind of noise are you trying to stop?
Airborne noise starts in the air, as voices, music, a television or a barking dog. It sets walls and floors vibrating slightly, and they pass the sound on to the other side. Impact noise starts when something strikes the structure directly: footsteps, dropped objects, chairs dragged across a floor, a door slammed in its frame. The two call for different fixes, and many complaints involve both.
- Voices and television through a shared wall are mostly airborne noise, which responds to added mass, decoupling and careful sealing.
- Footsteps and thumps from upstairs are impact noise, best reduced at the floor surface above or by decoupling the ceiling below.
- Low-pitched sound, such as bass from a sound system or the hum of mechanical equipment, is the hardest to stop and calls for heavier, well-separated assemblies.
- Noise from plumbing, ducts and appliances often travels through the structure and is best reduced at the source, with isolation pads, flexible pipe supports or quieter equipment.
How soundproofing works: mass, decoupling, damping, absorption and sealing
Most soundproofing assemblies combine several of these principles, because each one handles part of the problem. None of them is a single product you can add to a wall and forget.
- Mass: heavier layers, such as additional or denser gypsum board, are harder for sound to set in motion, so they block more airborne noise.
- Decoupling: separating the two faces of a wall or ceiling with resilient channels, isolation clips, staggered studs or a second, independent wall keeps vibration from passing straight through the framing, but only if nothing, not even one misplaced screw, bridges the gap.
- Damping: a viscoelastic compound sandwiched between two layers of board converts part of the vibration into heat, which helps with frequencies that mass alone lets through.
- Absorption: sound-absorbing insulation such as mineral wool or glass fibre in the cavity reduces resonance inside the wall or floor, and it works best combined with mass and decoupling.
- Sealing: sound leaks through any air gap, so the edges of each layer, electrical boxes and pipe penetrations are sealed; Natural Resources Canada lists acoustical sealant as a caulking meant to be sandwiched between materials rather than left exposed.
Common soundproofing projects: shared walls, basement ceilings, home offices and home theatres
Flanking spoils many projects: sound goes around the treated wall through the floor, the ceiling, a continuous joist, a duct or back-to-back outlets. Before choosing what to build, a good contractor traces the whole path from the noise source to your ear.
- Shared walls in semis, row houses and condos: usually a decoupled layer or a second independent wall on your side, with outlets and edges sealed, since you can rarely work on the neighbour's side.
- Basement ceilings: resilient channels or isolation clips, insulation between the joists and added gypsum board reduce noise between a basement suite or family room and the floor above, with extra care around ducts and recessed lights.
- Floors: a resilient underlayment beneath new flooring, or a floating floor, is the most direct way to cut footstep noise at its source, and carpet over a good pad also helps.
- Home offices: a solid-core door with seals, a sealed wall and absorbent finishes inside the room reduce what you hear and what others hear of your calls.
- Home theatres and music rooms: often a room within a room, with decoupled walls and ceiling, a sealed door and ventilation designed so it doesn't become a sound leak.
STC and IIC ratings: understanding soundproofing numbers
Assemblies are compared with two ratings. The Sound Transmission Class, or STC, describes how well a wall or floor blocks airborne sound in a laboratory test, and the Impact Insulation Class, or IIC, describes how well a floor and ceiling assembly resists impact noise such as footsteps. For both, a higher number means better performance.
Laboratory ratings describe an assembly built perfectly, with no side paths. In a real building, outlets, ducts, gaps and the surrounding structure lower what you actually get. That is the idea behind apparent ratings, which account for those paths: when the Régie du bâtiment du Québec updated the Construction Code, it aimed to improve soundproofing in dwellings, notably by introducing an apparent sound transmission index. When a contractor quotes a rating, ask whether it comes from a tested assembly that matches what will be built, and be wary of any promise of a specific number in your home.
Soundproofing between units: building code, fire separations and condo rules
Walls and floors between dwelling units have to meet building code requirements for both sound and fire. If your project creates a new unit, such as a basement apartment, or changes a separation between units, ask your municipality about permits before work starts.
Fire separations must stay intact. A wall or ceiling between units, or between a house and an attached garage, is built to slow the spread of fire and smoke, and soundproofing must not weaken it: fire-rated gypsum that is cut is restored to the same rating, penetrations are sealed with approved firestop products, and a tested assembly is rebuilt as tested rather than improvised. Ask the contractor to state in writing how the fire rating will be maintained.
In a condo, the walls, floors and ceilings between units are often common portions or governed by the building's rules, and many buildings set requirements for flooring underlay. Before any work, read the declaration of co-ownership or the bylaws and ask the condo board what is allowed and what approvals you need.
Realistic soundproofing expectations: what it can and can't do
Soundproofing reduces noise; it rarely eliminates it. A well-built retrofit can make a neighbour's conversation much harder to make out, but deep bass, heavy footsteps on a light wood-frame floor and noise that travels through the structure are stubborn. The more of the path you can treat, including the floor above or the neighbour's side, the better the result.
- Soundproofing takes space: a decoupled layer or a second wall makes the room slightly smaller and means moving outlets and trim, sometimes door and window casings.
- Foam panels, acoustic tiles and heavy curtains improve how a room sounds inside but do little to stop noise passing through a wall.
- Blowing insulation into an existing wall helps somewhat, but on its own it won't transform a thin shared wall.
- Doors, windows and ventilation openings are often the weak link, and a sealed solid door or an upgraded window can matter as much as the wall.
- In a house built before 1990, opening walls and ceilings can disturb asbestos, which Health Canada says was mainly used then to insulate buildings against cold and noise, so have suspect materials tested before cutting.
Soundproofing: frequently asked questions
Can I soundproof a shared wall from my side only?
Yes, and that is the usual situation. A decoupled layer or a second independent wall on your side, with the outlets and edges sealed, can make a real difference. The limit is flanking: if sound also travels through a shared floor, ceiling or joists, treating one wall won't catch it all. In a condo, check with the board first.
What is the difference between STC and IIC?
STC rates how well a wall or floor blocks airborne sound such as voices and music, while IIC rates how well a floor and ceiling assembly resists impact sound such as footsteps. Higher is better for both. Both are usually measured in a laboratory, so the result in your home also depends on flanking paths and workmanship.
Do resilient channels really work?
They can, but only when installed correctly. The most common failures are screws driven through the channel into the studs or joists, channels mounted the wrong way up, and cabinets or shelves fastened through the gypsum into the framing, each of which reconnects the two sides. Ask the contractor how they avoid these shortcuts for sound, or whether isolation clips suit your project better.
How can I reduce footstep noise from the unit above?
The most effective fix is at the source: a resilient underlayment, carpet with a good pad or area rugs on the floor above, which means working with the neighbour or, in a condo, the board. From below, a decoupled ceiling with insulation in the joist spaces helps, though low thuds are harder to stop than the sharper click of heels.
Do I need a permit for soundproofing work?
It depends on your municipality and the scope. Adding a layer of gypsum to an existing wall is often minor work, but creating a basement unit, altering a wall or ceiling between units, changing a fire separation or moving electrical boxes may require a permit, and electrical work goes to a licensed electrician. Call your municipality before you start.
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Written by the LokalMatch editorial team. Reviewed by Zubair Afzal on September 10, 2026. How we write and check our guides