What's the cost to install a sound-rated floor assembly in a second-storey addition?

Second-storey addition floor assemblies with sound ratings typically run $18 to $35 per square foot installed in Ottawa, depending on the level of isolation required and the complexity of the framing situation. For a typical 400 square foot addition, budget $7,200 to $14,000 for the complete floor-ceiling assembly.

What Goes Into a Sound-Rated Floor Assembly

A high-performing floor assembly is actually a layered system working from top to bottom. Starting at the top, you have your finished flooring — hardwood, tile, or LVP — sitting on a resilient underlayment (typically 3 to 6mm acoustic foam or cork at $0.50 to $1.50 per square foot) that cushions impact noise at the source. Below that is your subfloor, ideally two layers of 3/4-inch tongue-and-groove plywood with the seams staggered and Green Glue Noiseproofing Compound applied between layers at roughly $15 to $22 per tube. This damping layer converts vibration energy into heat before it ever reaches the joists.

Inside the joist cavity, Rockwool Safe'n'Sound acoustic mineral wool at $1.20 to $1.80 per square foot is the right choice — standard fibreglass batts provide significantly less sound absorption and are worth avoiding here. Then comes the ceiling assembly below, where the real magic happens for airborne sound. RSIC-1 sound isolation clips with hat channel, at roughly $4 to $7 per clip installed on 24-inch centres, decouple the ceiling drywall completely from the joists above. A double layer of 5/8-inch Type X drywall with Green Glue between the layers finishes the assembly, adding mass and damping simultaneously.

A well-executed version of this assembly can achieve STC 55 to 65 for airborne sound and IIC 50 to 60 for impact noise — comfortably exceeding the Ontario Building Code minimum of STC 50 and IIC 50 for floor-ceiling assemblies between dwelling units.

Ottawa's climate adds an important wrinkle here. In a second-storey addition, the floor assembly may also function as part of the thermal envelope if the space below is unheated or semi-conditioned. Vapour barrier placement must be carefully coordinated — it belongs on the warm side of the insulation, which in Ottawa's climate means the upper surface of the floor system. Getting this wrong while chasing acoustic performance can lead to condensation within the assembly, mould, and structural damage. This is a genuine concern in Ottawa given the extreme temperature differential between interior and exterior during our -25°C winters.

The most common mistake on these projects is short-circuiting the isolation clips — driving a screw through the hat channel directly into the joist defeats the entire decoupling system and can drop your STC rating by 10 points or more. Every penetration through the ceiling for pot lights, HVAC registers, or plumbing must also be carefully detailed with acoustic putty pads and fire-rated acoustic sealant, or those gaps will bleed sound regardless of how well the main assembly performs.

Because this is new construction within an addition, a building permit from the City of Ottawa is required, and the floor assembly must meet OBC minimums at minimum. If the addition connects to a party wall situation — common in Barrhaven townhouses or Centretown semi-detached homes — the requirements become even more specific.

For a project like this, it is genuinely worth sitting down with an experienced soundproofing contractor before framing is complete — the easiest and most cost-effective time to build in proper isolation is before the subfloor goes down and the ceiling is closed. You can find soundproofing professionals serving the Ottawa area through the Ottawa Contractor Directory at justynrookcontracting.com/directory, where you can review contractor profiles and get in touch directly for quotes.