How to Soundproof a Room
During a Renovation

If you're putting drywall up, this is your one shot to soundproof correctly. After the rock is on, your options shrink to area rugs and apologies.

Most of the soundproofing I do in Ottawa is in basement legal suites, home theatres, second-storey home offices over the kitchen, and shared walls in semi-detacheds. The four principles below apply to all of them.

The four levers (in order of effectiveness)

Every legitimate soundproofing strategy uses one or more of these four levers. Skip any of them and your wall underperforms.

1. Mass. Heavy materials block sound. Period. This is why two layers of 5/8" drywall beats one layer of 1/2".
2. Decoupling. Sound travels through structure. Break the structural connection between the noisy side and the quiet side, and you cut that path.
3. Absorption. Cavity insulation absorbs energy bouncing inside the wall. Roxul Safe'n'Sound is the industry default.
4. Sealing. Sound leaks through gaps the same way water does. Outlets, gaps under doors, register cuts. All of them matter.

You'll see soundproofing products that claim to do everything in one step. They don't. Real performance comes from stacking these four levers.

STC ratings, and what they actually mean

STC stands for Sound Transmission Class. It's a single number that rates how well an assembly blocks airborne sound (voices, TV, music). Higher is better.

For Ottawa renovations, here's the rough scale I work to:

• STC 30-35: Standard interior wall. Loud speech is intelligible through it.
• STC 40-45: Decent privacy. Loud speech is audible but not intelligible. This is the Ontario Building Code minimum for shared walls in legal duplexes (Code calls for STC 50, but real-world post-construction often comes in around 45).
• STC 50-55: Loud speech inaudible, music faintly audible. Good for bedrooms over kitchens, basement suites, home offices.
• STC 60+: Studio-grade. Drum kits, full home theatres at reference volume.

The OBC requires STC 50 between dwelling units in a duplex or triplex. If you're doing a basement renovation in Ottawa with a legal secondary suite, this is the target.

"Going from STC 35 to STC 50 is a noticeable change. Going from 50 to 55 is a small one. Past 55 you're chasing diminishing returns at fast-rising cost."

Lever 1: Add mass

Drywall blocks sound roughly in proportion to its weight. The cheapest, most reliable mass upgrade is doubling up.

What I spec for shared walls in basement suites:

• Two layers of 5/8" Type X drywall on the suite side
• One layer of 5/8" Type X on the homeowner side
• Green Glue damping compound between the two layers on the suite side (one tube covers roughly a 4x8 sheet)

That alone, with cavity insulation, gets you to STC 50 on a wood-stud wall. The Green Glue between the two layers acts as a constrained-layer damper, converting acoustic energy into a tiny amount of heat.

Lever 2: Decouple the drywall

If your noise problem is bigger than mass alone can fix, decouple the wall. The two methods I use:

Resilient channel

RC-1 (sometimes called "hat channel" but technically resilient channel is the Z-shaped one) is screwed horizontally across the studs every 24 inches. The drywall hangs off the channel, not the studs.

The catch: RC fails if even one drywall screw goes through the channel into a stud. That short-circuits the decoupling. I've seen rooms tested before and after a single missed screw was found and removed; it changed STC by 4-5 points.

Hat channel + sound clips

This is what I spec for serious projects. Sound clips (PAC International RSIC-1 or similar) screw to the studs; hat channel snaps into the clips; drywall hangs off the hat channel. The clips have a rubber isolator that breaks the structural path almost completely.

Cost driver: clips are priced each and hat channel by the foot, so the spend scales with wall area and clip spacing. On a 10x12 room the clips and channel are a modest add beyond standard framing, well worth it for the decoupling they buy.

Lever 3: Absorb inside the cavity

The cavity between studs needs insulation. Without it, your wall is basically a drum.

I use Roxul Safe'n'Sound. It's mineral wool, R-value around R-15 in a 2x4 wall (not its primary purpose but a bonus), and it's denser than fibreglass batts which makes it better at absorbing low frequencies.

Spray foam is the wrong choice for soundproofing. Closed-cell foam is rigid, which means it transmits structural vibration. It's great for thermal performance and air sealing; it underperforms for sound versus fluffy mineral wool.

Lever 4: Seal every gap

This is the lever everyone skips. Doesn't matter how good your wall assembly is if there's a half-inch gap under the door or an electrical box that goes all the way through.

The seal-the-gap checklist:

• Acoustic caulk around the perimeter of every drywall sheet, top and bottom plates, and around every penetration. Tremco or OSI brand. A few dollars a tube, and one of the cheapest STC gains you can buy.
• Putty pads on every electrical box. They wrap around the box and seal the holes where wires enter. Inexpensive per box.
• Solid-core doors instead of hollow-core for any room you actually want quiet. STC for a hollow door: about 17. For a solid-core: about 30.
• Door sweeps and weatherstripping. A standard interior door has a 3/8" gap underneath. That gap alone drops a wall's effective STC by 8-10 points.
• Offset HVAC registers. A return-air vent on the shared wall is a sound highway. Reroute through the ceiling or use a flex duct that takes a 90-degree turn.

Floor and ceiling matter too

Walls are only one path. If you're soundproofing a basement suite, the ceiling between the suite and the homeowner above carries the most sound, mostly footstep impact.

For ceilings I spec:

1. Roxul in the joist bay
2. Sound clips and hat channel under the joists
3. Two layers of 5/8" drywall with Green Glue between
4. Acoustic caulk at every perimeter

For floors above, the homeowner's side, the highest-impact upgrade is an acoustic underlay (Acousti-Tech or similar) under whatever finished flooring goes down. A good underlay drops impact noise (kids running, dropped pots) by 10-15 dB.

What drives the cost

For a typical basement suite shared wall in Ottawa, the price climbs with the assembly you choose. Each step up adds material and labour, and buys you STC points:

• Standard wall (R12 fibreglass, single drywall): the cheapest assembly, and the worst performer at roughly STC 35.
• Mass-loaded wall (Roxul + double drywall + Green Glue): a moderate step up in cost for roughly STC 45.
• Decoupled + mass-loaded (clips, hat channel, double drywall, Green Glue, Roxul): the most expensive assembly, and the one that reaches roughly STC 52-55.

So the spend is driven by wall area and which of those three assemblies you build. The decoupled assembly is what you want for any legal secondary suite, and we put the exact assembly and its cost into a clear itemized proposal before any rock goes up.

What soundproofing won't fix

Two things I get asked about that no amount of wall assembly can solve.

First: low-frequency bass. A subwoofer in the apartment below will travel through the building's structure (foundation, joists, posts) regardless of how well your wall is built. Bass needs structural decoupling, which usually means floating the entire floor on rubber pucks, which usually isn't worth the cost in a residential project. If your noise problem is bass, the realistic fix is asking the neighbour to lower it, not the wall.

Second: flanking paths. Sound that gets around your perfect wall by traveling through the floor, ceiling, or a shared duct. A shared HVAC duct between two apartments is a sound highway no wall can compete with. Same for a shared plumbing chase. If you're soundproofing a basement suite, you have to look at every shared structural element, not just the wall you're rebuilding.

The honest version: soundproofing is about reducing intelligibility, not eliminating sound. STC 50 means you'll still hear that someone is talking next door; you just won't make out the words. That's the realistic goal in a wood-framed Ottawa home.

Dream Touch builds about 20 basement suites a year in Ottawa, including the soundproofing required to pass OBC inspection on shared assemblies. If you want it spec'd right the first time, call 613-862-4555.