Can I soundproof a single wall in my Toronto semi-detached without tearing out all the existing drywall?

Yes, you can add soundproofing to a single shared party wall in a Toronto semi-detached without removing the existing drywall, and it's one of the most common soundproofing requests we see across the GTA. The approach involves building a new sound-isolation layer directly over the existing wall surface, which avoids the mess, cost, and disruption of a full tear-out.

The most effective method is to apply Green Glue Noiseproofing Compound directly to a new layer of 5/8-inch drywall and then screw that second layer over the existing wall. Green Glue is a viscoelastic damping compound that converts sound energy into tiny amounts of heat, and when sandwiched between two rigid layers it can improve the wall's STC (Sound Transmission Class) rating by 8-12 points. In the GTA, a tube of Green Glue runs about $18-$25, and you'll need roughly two tubes per 4x8 sheet. The new layer of 5/8-inch drywall costs $18-$26 per sheet. For a typical semi-detached party wall of around 120-160 square feet, you're looking at $1,500-$3,500 installed including materials, taping, finishing, and painting — a fraction of a full tear-out rebuild.

For even better results, Toronto drywall contractors often recommend installing resilient channel (also called hat channel or RC-1) horizontally across the existing wall at 24-inch intervals before attaching the new drywall layer. Resilient channel mechanically decouples the new drywall from the wall structure behind it, meaning sound vibrations travelling through the framing don't transfer directly to your new drywall surface. This adds roughly $1.50-$2.50 per square foot in materials and labour but can push the STC improvement to 15-20 points when combined with Green Glue. The critical installation detail here is that every single screw must go through the drywall and into the resilient channel only — if even one screw penetrates through the channel and into a stud behind it, that screw acts as a sound bridge and short-circuits the entire isolation assembly. This is why professional installation is strongly recommended.

Another option gaining popularity in GTA renovations is QuietRock soundproof drywall, which has a viscoelastic polymer core built right into the board. A single layer of QuietRock over the existing wall provides roughly the same performance as the Green Glue sandwich method but with faster installation since there's only one layer to hang and finish. QuietRock sheets run $55-$90 per 4x8 sheet in the GTA, so materials cost more, but labour is less since you're hanging one layer instead of two.

There are a few things to be aware of with any over-the-existing-wall approach. You'll lose about 1 to 1.5 inches of room depth per wall you treat — not a huge amount, but it does mean adjusting electrical outlet boxes, light switches, window and door casings, and baseboards. Your electrician will need to extend outlet boxes to reach the new wall surface, and this may require a permit depending on the scope. Also, sound doesn't just travel through the party wall — it flanks around through the floor, ceiling, electrical outlets, and any shared structural elements. Treating the party wall alone typically produces a noticeable improvement, but if the noise issue is severe, you may need to address the ceiling and floor connections as well for a complete solution.

For Toronto semi-detached homes specifically, the party wall is often a double-stud or masonry construction depending on the era. Pre-war semis in neighbourhoods like the Annex, Riverdale, and Leslieville may have a solid brick party wall, which already provides decent mass-based sound isolation — adding a decoupled drywall layer over that can be remarkably effective. Post-war semis in Scarborough, East York, and North York are more likely to have wood-framed party walls with less inherent sound blocking, so the improvement from adding a soundproofing layer will be more dramatic.

This is absolutely a project for a professional drywall contractor with soundproofing experience. The resilient channel installation is unforgiving — one mistake compromises the whole assembly — and the taping and finishing of the new surface needs to be seamless. Budget $2,500-$5,000 for a single party wall done properly with resilient channel and a Green Glue drywall sandwich, including all finishing work. Browse drywall professionals in your area through the Toronto Construction Network directory.