What's the price to add a second window pane behind existing heritage windows for sound control?

Adding a secondary interior window pane behind existing heritage windows — commonly called a secondary glazing system or interior storm window — typically costs between $500 and $1,400 per window in Ottawa, depending on the window size, glass specification, and mounting system. For a heritage home in Sandy Hill, the Glebe, or New Edinburgh with 10 to 15 windows, that puts the total project cost at $5,000 to $21,000. This approach is often the best option for heritage properties because it leaves the original exterior window completely untouched while delivering substantial noise reduction.
The principle is straightforward: you mount a separate sealed glass panel on the interior side of the existing window frame, creating an air gap of 2 to 4 inches between the original glass and the new pane. This air gap is the key to performance — the wider the gap, the better the sound isolation, especially at lower frequencies like traffic rumble. A 4-inch air gap with 6mm laminated glass on the interior pane can achieve a combined assembly performance of STC 40 to 48, compared to STC 24 to 28 for a typical single-pane heritage window alone. That is a transformative difference — the kind that turns a bedroom facing a busy street from unliveable to genuinely quiet.
Material costs break down as follows: a custom-sized laminated glass panel runs $150 to $400 depending on size, a magnetic or compression-seal mounting frame (aluminum or wood, colour-matched to the interior trim) costs $100 to $350, and perimeter acoustic seals add $30 to $80. Labour for professional installation runs $200 to $550 per window in Ottawa. The magnetic-mount systems are particularly popular for heritage homes because they allow easy removal for cleaning or seasonal ventilation — you simply pull the interior panel away from its magnetic seal, clean both panes, and snap it back.
There are important installation details that affect both cost and performance. The air gap between panes must be sealed airtight — any air leakage dramatically reduces the sound isolation. If the original heritage window is itself leaky (common with old rope-and-weight sash windows), you may also need to add weatherstripping to the original window ($50 to $150 per window) for the secondary glazing to reach its full potential. In Ottawa's climate, the air gap can create condensation issues if not properly detailed — a small silica gel desiccant packet in the air cavity or micro-ventilation to the interior prevents moisture buildup. The secondary pane should always be on the warm side (interior) to minimize condensation risk, which is the natural position for this installation.
Heritage Conservation District approvals are generally not required for interior-only modifications, but it is wise to confirm with the City of Ottawa if your property has a heritage designation. This is one of the most effective and least invasive soundproofing upgrades for Ottawa's older homes — Ottawa Soundproofing's Sound IQ can help you evaluate whether secondary glazing will address your specific noise problem before you invest.Looking for experienced contractors? The Ottawa Construction Network connects homeowners with qualified professionals:HomeupgradersRenoMotion Inc.BFI RenovationsVanguard EnvironmentalTitley ConstructionView all contractors →