How do I fix drafts around old windows in an insulated New Brunswick home? | Insulation IQ?

Drafts around windows are one of the most common and most frustrating comfort complaints in New Brunswick homes, particularly in older houses in cities like Fredericton, Saint John, and Miramichi where double-hung wood-framed windows from the 1960s through 1990s are still common. The good news is that most window drafts can be fixed without replacing the windows, and when addressed properly, the improvement in comfort and energy savings can be significant.

Understanding the source of the draft matters before you start applying caulk. Window drafts come from two distinct sources: air leakage through the window assembly itself (around the sash, through the glazing system, or via failed weatherstripping), and air leakage through the rough opening — meaning the gap between the window frame and the surrounding wall framing. These require different solutions.

For drafts through the window assembly, the primary fix is weatherstripping replacement. On older double-hung windows, the sash channels wear out over decades and no longer seal against the frame. Foam tape, V-strip bronze weatherstripping, or pile weatherstripping can be installed in the sash channel to restore the seal. Bronze V-strip is the most durable choice for New Brunswick's wide temperature swings — foam compresses and hardens after a few winters, while bronze holds its shape for decades. Expect to spend $10–$30 in materials per window for a DIY weatherstripping replacement.

For drafts coming through the rough opening gap, the situation is more involved. Every window is installed in a rough opening slightly larger than the window frame, and that gap must be filled with insulation and sealed with an air barrier. In older homes, this gap was often packed with fibreglass batts, which insulate against conducted heat but do nothing to stop air movement. Over time, the batts sag or shift, leaving uninsulated voids, and the inner and outer air barrier is often just a bead of caulk that has cracked and pulled away from the trim.

The correct fix for a rough opening draft involves carefully removing the interior window casing trim, inspecting the gap between the frame and framing, and either injecting low-expansion spray foam (never high-expansion, which can bow window frames out of square) or packing the gap tightly with a material that also acts as an air barrier. Low-expansion foam is ideal because it seals and insulates simultaneously. Once the foam has cured, reinstall the trim and apply a fresh bead of paintable caulk along every interior joint where trim meets wall and where trim meets window frame.

On the exterior, re-caulk the joint between the window flange (or brick moulding) and the exterior cladding. Exterior caulk in New Brunswick should be rated for temperatures down to at least -40°C and should be paintable if the window surround is painted. Polyurethane caulk outperforms latex in high-movement joints, which window perimeters always are due to the seasonal expansion and contraction of wood framing.

Another overlooked source of drafts is the interior window well itself — the drywall or plaster returns that surround the window on the inside. Especially in walls with fibre or batt insulation, the interior of the wall cavity behind the window well can act as a conduit for cold air drawn down from the attic or up from the basement by stack effect. If resealing the window assembly and rough opening does not eliminate the draft, remove a section of the window well casing and inspect whether the insulation in the wall cavity above and below is continuous and air-sealed.

For windows on exterior walls that also show condensation or frost on the glass, this indicates the window glass or frame is too cold, which usually means the window itself has lost its thermal value (failed IGU seal in a double-pane unit) rather than just an air sealing problem. In those cases, the sash or entire window unit should be replaced. In Climate Zone 6, the NB Building Code requires windows with a minimum energy rating — a qualified installer can advise whether replacement makes more economic sense than continued repair.

Weatherstripping and caulking supplies are inexpensive — most homeowners can address 6–10 windows for well under $200 in materials. For homes where the rough opening gaps are extensive or where the windows are in difficult-to-access locations, professional air sealing contractors working in the Fredericton and Saint John area can complete this work efficiently, and it is eligible for reporting on an EnerGuide audit as part of a Canada Greener Homes Grant application. New Brunswick Insulation is a good starting point to find experienced contractors in your area.

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Looking for experienced contractors? The New Brunswick Construction Network connects homeowners with qualified professionals:

• Brunswick insulation & roofing
• Thirty Four Renovations
• Arctic Fox Construction Inc.
• Gionetterenovations
• 3Tone Construction Ltd