By Trust Build Windows and Doors ·
The first sign is usually the cushion. Someone in an Old North four-square or Edwardian cottage finally notices the window seat cushion is always a little damp, even in July, and assumes it's a plumbing problem somewhere upstairs. It isn't. It's the bay window underneath it, and it's been quietly failing for longer than anyone in the house realized.
Old North has more bay windows per block than almost anywhere else in London. Walk along Waterloo Street or through the blocks around Victoria Park and you'll see them on nearly every second house — projecting three-sided windows under their own little hip roof, often with a built-in bench seat tucked beneath the glass. Builders used them constantly in this neighbourhood's peak construction years because they pulled extra light into front parlours and dining rooms while giving a plain Edwardian or foursquare facade some visual depth, cheaply. A century later, that same structure is the reason so many of these homes have a soft spot nobody wants to talk about.
Here's the part that surprises people who call about a drafty window and end up talking about structure instead. A bay window isn't one unit — it's three (sometimes five) units joined at angles, sitting on a framed-out box that cantilevers past the foundation wall. That box has its own roof, its own flashing, and its own sill ledge exposed to weather on three sides instead of one. The original wood sashes held up fine for decades. But once the glazing starts failing — fogged double-pane units from a 1980s or '90s retrofit, or original single glazing nobody upgraded — water finds its way into that box faster than it does on a flat wall opening. The cushion gets damp long before anyone sees rot at the corners.
I'd rather homeowners catch this at the window-seat-cushion stage than at the sagging-roofline stage, which is where a lot of Old North bay windows end up if nobody looks closer. By the time the little roof over the bay has visibly dropped half an inch at the outer corner, you're not just replacing glass — you're often rebuilding the box frame underneath, which is a bigger job and a bigger bill.
What a proper bay window replacement actually involves here
Because Old North is almost entirely solid brick construction, not brick veneer over wood frame like newer subdivisions, a straightforward retrofit insert isn't always the right call for a bay. Retrofit works well when the existing frame is structurally sound and you're mainly replacing failed glass units. But if there's rot in the box sill or header, a proper stud-to-stud or brick-to-brick rebuild of that projecting structure is usually the better long-term move, even though it costs more upfront. Saving a compromised bay frame with a quick insert just moves the water problem a few years down the road.
Glazing choice matters more on a bay than on a standard window, too, simply because there's more glass surface facing outward on three exposed angles instead of one. For a west- or north-facing bay in an Old North winter, pairing an Energy Star-rated vinyl or hybrid frame with a solar-control Low-E coating — Cardinal's Lowe²-272 is a common, well-performing choice for this climate — keeps the bench seat usable in January instead of being the coldest spot in the room. Triple glazing is worth pricing out specifically for bays that catch a lot of winter wind, since the extra pane does more work when there's three times the glass area to protect.
A note on heritage review: parts of Old North, including pockets like the Bishop Hellmuth area, carry heritage conservation district status, which can mean an extra step before exterior changes to street-facing windows are approved. It's not something to skip or guess about — check with the City of London's heritage planning staff before ordering anything if your property sits inside one of those designated areas. Most bay window replacements that keep the original proportions, muntin pattern, and roofline sail through without issue.
Financing is one area where there's genuinely good news for a project like this. Trust Build offers 0% interest financing on windows and doors, which matters for a bay replacement since the structural rebuild version of this job runs meaningfully higher than a standard window swap. We've now done this kind of work for more than 8,700 homeowners across Ontario — enough of them in older London neighbourhoods that we've gotten familiar with exactly how Old North's bay boxes are built and where they tend to fail first.
