How effective is adding a second layer of drywall for soundproofing in an existing home?

Adding a second layer of drywall is one of the most effective and economical soundproofing upgrades you can make to an existing home, typically improving sound blocking by 8-12 decibels when done properly. This translates to roughly a 50-75% reduction in perceived noise levels — a significant improvement that most homeowners notice immediately.

How Double Drywall Works for Sound Control

The effectiveness comes from adding mass to the wall assembly, which is one of the fundamental principles of sound blocking. Sound waves lose energy when they encounter heavy, dense materials. A single layer of 1/2-inch drywall weighs about 2 pounds per square foot, while adding a second layer of 5/8-inch Type X drywall brings the total mass to roughly 4.5 pounds per square foot — more than doubling the sound-blocking capability.

However, the real magic happens when you use Green Glue Noiseproofing Compound between the two drywall layers. This viscoelastic damping compound converts sound energy into tiny amounts of heat, adding another 3-5 decibels of improvement. A properly installed double drywall system with Green Glue can achieve STC ratings of 45-50 compared to STC 33-38 for a standard single-layer wall.

In Ottawa's housing stock — from Centretown condos to Kanata subdivisions — this upgrade is particularly valuable because most homes built before 2000 have minimal sound isolation between rooms. The Ontario Building Code requires STC 50 for party walls between dwelling units, but interior walls in single-family homes have no minimum requirements, often performing at just STC 30-35.

Installation considerations for Ottawa homes include working around the climate — Green Glue requires temperatures above 10°C to cure properly, so winter installations in unheated spaces need temporary heating. The compound takes 7-30 days to fully cure, with performance improving over time. You'll also need to extend electrical boxes and trim work to accommodate the additional 5/8-inch thickness.

Cost-effectiveness makes this upgrade attractive — expect to pay $4-$8 per square foot for materials and professional installation in the Ottawa area. For a typical 10x8 foot bedroom wall, that's $320-$640 total. Compare this to a full wall rebuild with resilient channels and isolation clips at $15-$25 per square foot, and double drywall offers excellent value for moderate noise problems.

The main limitations are that this approach doesn't address flanking paths (sound traveling through connected structures) and provides minimal improvement for low-frequency sounds like bass or footsteps from above. It's most effective for airborne sounds like voices, TV, and music. Also, if the existing wall has significant air leaks around outlets, doors, or baseboards, those must be sealed with acoustic caulk for the upgrade to reach its full potential.

For serious noise problems or new construction, combining double drywall with resilient channels or sound isolation clips can achieve STC ratings of 55-65, but the cost jumps significantly. Most Ottawa homeowners find that properly installed double drywall with Green Glue provides the best balance of performance and affordability for typical noise concerns.

For a project like this, it's worth consulting with an experienced soundproofing contractor who can assess whether your specific noise problem will respond well to this approach and ensure proper installation for maximum effectiveness.