How much would it cost to retrofit a fire-rated and sound-rated wall between units in a duplex?

Retrofitting a fire-rated and sound-rated party wall between units in an Ottawa duplex typically costs between $5,000 and $12,000 per wall, depending on wall height, length, complexity of existing services, and the target STC rating. For a standard 10-foot by 8-foot party wall, most Ottawa homeowners land in the $6,000 to $9,000 range for a professionally installed assembly that meets both the Ontario Building Code fire separation requirements and achieves a comfortable STC 55 to 60 rating — well above the OBC minimum of STC 50.
What the Assembly Looks Like and What Drives Cost
The most common retrofit approach involves building a new decoupled wall layer on your side of the existing party wall. This typically means installing sound isolation clips (such as RSIC-1 at $4 to $7 each) and hat channel to the existing wall, filling the cavity with Rockwool Safe'n'Sound acoustic mineral wool, then finishing with a double layer of 5/8-inch Type X drywall with Green Glue compound between the layers. This assembly maintains the existing fire rating while adding substantial sound isolation. The material cost alone runs roughly $8 to $14 per square foot, with labour adding another $10 to $16 per square foot depending on the complexity of electrical, plumbing, and HVAC penetrations that need to be addressed.
The biggest cost variable in duplex retrofits is dealing with existing services in the wall. Electrical outlets, light switches, plumbing pipes, and HVAC ducts all create penetrations that must be individually sealed with acoustic putty pads and fire-rated acoustic caulk to maintain both the fire and sound ratings. In older Ottawa duplexes — particularly in neighbourhoods like Centretown, Old Ottawa South, and the Glebe — you may encounter knob-and-tube wiring, outdated plumbing, or unconventional framing that adds to the scope and cost. Budget an additional $1,000 to $3,000 if electrical work needs to be brought up to code as part of the project.
Because this work modifies a fire-rated assembly between dwelling units, a building permit from the City of Ottawa is required. Expect permit fees of $150 to $400 and plan for an inspection. The permit process is straightforward — apply through ottawa.ca or 3-1-1 — but factor in two to four weeks for approval. Your contractor must ensure the finished assembly carries a tested fire rating, which is why using Type X drywall and fire-rated sealants is non-negotiable, not optional.
One approach that saves money is treating only your side of the wall, which is the standard practice since you typically cannot access or modify your neighbour's side. Even a single-side retrofit with proper decoupling and mass can improve the wall's performance by 15 to 20 STC points. For a duplex party wall project, consulting with an experienced soundproofing professional is essential to get the fire and sound ratings right the first time — Ottawa Soundproofing's Sound IQ can help you understand what your specific wall needs.Looking for experienced contractors? The Ottawa Construction Network connects homeowners with qualified professionals:HomeupgradersRenoMotion Inc.L.L. RenovationOttawa CaulkingTiptop ContractingView all contractors →