Does adding a second layer of drywall significantly reduce noise between floors in a GTA townhouse?

Adding a second layer of drywall to the ceiling below will provide a noticeable but modest improvement in airborne sound reduction — typically an STC improvement of 3–6 points on its own — but it does very little to reduce impact noise like footsteps, which is usually the primary complaint in GTA townhouses. To get a significant improvement, the second layer needs to be combined with other strategies, particularly decoupling and damping.

The reason a simple second layer of drywall has limited effect comes down to physics. Sound transmission through a wall or ceiling assembly is governed by mass, decoupling, damping, and absorption. Adding a second layer of 5/8-inch drywall increases the mass of the ceiling by about 2.5 pounds per square foot — and while more mass does block more sound, the improvement follows a logarithmic curve. You need to double the mass to gain roughly 6 STC points, and a second layer of drywall does not quite double the mass of the entire assembly (which includes the joists, subfloor, and flooring above). More importantly, if the second layer is screwed directly through the first layer into the same joists, both layers vibrate together as a single unit, significantly limiting the benefit.

The key to making that second layer effective is adding Green Glue Noiseproofing Compound between the two drywall layers. Green Glue is a viscoelastic damping compound that converts sound vibration into tiny amounts of heat. Apply two tubes ($15–$20 per tube in the GTA) per 4x8 sheet in a random pattern, press the second sheet against the first, and screw it through. This combination of mass plus damping typically yields an STC improvement of 8–12 points over a single layer — roughly twice the improvement of adding drywall alone. The installed cost for a Green Glue plus second drywall layer on a typical townhouse ceiling (approximately 400–600 square feet) runs $2,500–$5,000 including materials, labour, taping, and finishing.

For even better results, particularly for impact noise (footsteps, dropped objects, children running), the second drywall layer should be mounted on resilient channel rather than screwed directly through the existing ceiling. This means removing the existing ceiling drywall, installing resilient hat channel perpendicular to the joists at 16- or 24-inch spacing, adding R-20 batt insulation in the joist cavities (if not already present), and then hanging new drywall on the resilient channel. Adding a second layer with Green Glue on top of that gives you the full package: decoupling (resilient channel), absorption (insulation), mass (double drywall), and damping (Green Glue). This assembly achieves STC 55–60 and provides meaningful impact noise reduction. The cost is higher — $5,000–$10,000 for a typical townhouse floor — because it involves removing and disposing of the existing ceiling, which is a messy, labour-intensive job.

GTA townhouses have specific challenges that affect this decision. Most townhouses built in the 1990s–2010s across Mississauga, Brampton, Markham, Vaughan, and Richmond Hill were built with engineered floor trusses that are excellent structurally but less massive than solid lumber joists, meaning they transmit more vibration. The original ceiling in many of these townhouses is a single layer of 1/2-inch drywall — already below what most acousticians would recommend for floor/ceiling separations. The Ontario Building Code requires STC 50 for separations between dwelling units (shared walls between townhouse units), but the floor/ceiling assembly within your own unit has no minimum STC requirement — meaning the builder likely installed the minimum.

There are also practical considerations for GTA townhouse owners. Adding a second layer of drywall to the ceiling reduces your ceiling height by about 5/8 inch (16mm). In a standard 8-foot ceiling, this is barely noticeable. In a basement with lower ceilings, it could matter — the Ontario Building Code requires minimum 1.95-metre clear ceiling height in basements. The existing ceiling texture (stipple or popcorn, common in 1990s–2000s GTA townhouses) does not need to be removed before adding the second layer if you are using Green Glue, though the surface should be scraped flat enough for good contact. All pot lights, electrical boxes, and smoke detectors must be extended to the new ceiling surface.

The bottom line: a second layer of drywall alone is a modest improvement. A second layer with Green Glue is noticeably better. A resilient channel system with insulation, double drywall, and Green Glue is the real solution. For townhouse noise between floors, the resilient channel approach is worth the extra investment — footstep noise is what drives most GTA townhouse owners to soundproof in the first place, and only decoupling addresses impact noise effectively. Need help finding a drywall installer? Toronto Drywall Installers can match you for free.