What's the cost per room to add blown-in dense-pack cellulose to existing interior wall cavities?

Adding blown-in dense-pack cellulose to existing interior wall cavities typically costs $800 to $2,200 per room in Ottawa, depending on room size, number of walls being filled, wall height, and accessibility. For a standard 10×12-foot bedroom with three interior walls (one shared with a hallway, two with adjacent rooms), expect to pay roughly $1,200 to $1,800 including patching and painting touch-ups. Ottawa labour rates for this work are approximately 10–15% below what you would pay in the Greater Toronto Area, making it one of the more affordable acoustic upgrades available.
Dense-pack cellulose is installed by drilling small holes (typically 2–3 inches in diameter) into each stud cavity, either from inside the room or from an adjacent space, then blowing the cellulose in at a density of 3.5 to 4.0 pounds per cubic foot. At this density, the material resists settling and provides meaningful sound absorption — though it is important to understand what dense-pack cellulose can and cannot do. It fills the cavity and absorbs mid-to-high-frequency airborne sound, which noticeably reduces voice transmission and general household noise between rooms. However, it does not decouple the wall structure, so low-frequency sounds like bass music or impact noise will still transmit through the studs themselves. On its own, dense-pack cellulose in a standard single-stud wall might improve the assembly by 3–5 STC points — noticeable but not transformative.
The real value of dense-pack cellulose comes when it is part of a layered approach. If you are already planning to add a second layer of drywall with Green Glue compound or install resilient channels, filling the cavities with dense-pack cellulose first maximises the performance of those additional treatments. For homeowners in neighbourhoods like Barrhaven, Kanata, or Stittsville with relatively modern drywall-over-stud construction, this combination can bring a standard interior wall from roughly STC 33 up to STC 48–52 — a substantial improvement in everyday comfort.
One practical advantage of dense-pack cellulose over batt insulation like Rockwool Safe'n'Sound is that it can be installed in existing walls without removing the drywall, which saves considerably on labour and finishing costs. The trade-off is that you cannot inspect the cavity for issues, verify complete coverage, or address electrical boxes and other penetrations the way you can with an open-wall installation. If your walls have significant air leaks around outlets, switches, or plumbing penetrations, those flanking paths will limit the benefit of any cavity fill. Budget roughly $50–$100 per room for acoustic putty pads on electrical boxes if you want to address those weak points at the same time.
Scheduling matters in Ottawa — winter installations in unheated spaces require the blowing equipment and material to be at reasonable working temperature, though for interior walls this is rarely an issue. For a personalised assessment of which rooms would benefit most from dense-pack cellulose, Sound IQ can help you understand your options and connect with contractors who specialise in retrofit acoustic insulation.Looking for experienced contractors? The Ottawa Construction Network connects homeowners with qualified professionals:Justyn Rook ContractingRenoMotion Inc.Nic’s D.U.C.T Works IncDenys Builds Designs RenovationsLeeds Property MaintenanceView all contractors →