How much does it cost to run ductwork through a Toronto home soffit for a second-floor reno?

Running ductwork through a soffit for a second-floor renovation in Toronto typically costs $800–$3,500 per run, depending on the length of the run, the number of fittings required, material choice, and how accessible the soffit chase is from the basement or main floor mechanical room.

This is one of the most common ductwork challenges in GTA second-floor renovations, and it is worth understanding what drives the cost before you get quotes.

What the Work Actually Involves

A soffit duct run for a second floor means building a concealed chase — usually framed with drywall over a rectangular steel duct — that travels vertically from the main trunk line in the basement or main floor up through the wall or closet cavity, then horizontally along the ceiling of the main floor (inside the soffit) to reach a point below the second-floor register. From there, a short branch run connects to the floor register above. Each 90-degree turn, transition fitting, and offset adds both material cost and labour time.

The duct itself is almost always rectangular galvanized steel for the main soffit run — typically 8×4 or 10×4 inch profile — to keep the soffit as slim as possible while still delivering adequate airflow. Branch connections to individual registers use 6-inch round flex duct, kept short and pulled taut. Material costs for the steel duct and fittings alone run $150–$500 per run depending on length. Labour in the GTA for a sheet metal worker runs $85–$130 per hour, and a single soffit run with two or three offsets typically takes 4–8 hours.

GTA-Specific Considerations

Toronto's housing stock matters here. In a post-war Scarborough or North York bungalow being converted to a two-storey addition, the existing trunk duct is often undersized for the added second-floor load — meaning the soffit run may need to connect to an upgraded trunk, not just tap into the existing one. In an older Toronto semi or detached in areas like Leslieville, Roncesvalles, or the Annex, wall cavities are often narrower than modern framing, making vertical runs trickier and requiring custom-fabricated fittings.

Condensation is also a real concern in GTA homes. If any portion of the soffit run passes through an exterior wall or an uninsulated section of the soffit adjacent to an exterior, the duct must be wrapped with R-8 duct insulation to prevent sweating in summer when cold supply air meets warm humid conditions. Skipping this step leads to water stains on the drywall soffit within one or two cooling seasons.

Permits are worth flagging. If this soffit run is part of a larger second-floor renovation that includes new construction or a significant duct system modification, a City of Toronto mechanical permit is likely required. Permit fees typically run $200–$500 for mechanical work of this scope.

Practical Tips

Get quotes that specify the duct size, number of fittings, sealing method (mastic is the standard — not duct tape), and whether the drywall soffit framing and finishing is included or separate. Many ductwork contractors do the sheet metal only and hand off the framing and drywall to a carpenter — make sure you know who is responsible for what. Also confirm the contractor will size the new branch run based on the actual heating and cooling load of the second-floor room, not just whatever fits conveniently. An undersized duct in a soffit that is already closed in is very expensive to fix later.

Hire a professional for this work. Soffit duct runs involve custom sheet metal fabrication, proper sizing for second-floor loads, sealing all joints with mastic, and coordinating with drywall finishing. This is not a DIY project, and getting it wrong means tearing open finished ceilings to fix it.

Toronto Ductwork can match you with a local ductwork contractor experienced in second-floor renovation work — get in touch for a free match, or browse HVAC and ductwork professionals through the Toronto Construction Network directory at torontoconstructionnetwork.com/directory?trade=hvac.