Bay and bow windows
Bay and bow windows: glass, seat, roof and support
From inside, a bay is a nook with a seat. From outside, it's a small structure: window units joined at angled posts, a roof cap, a platform and supports tying it to the house. A fogged pane and a sagging seat are different jobs. We match you with an independent local window professional who checks the whole assembly in your home and says so when one new sealed unit will do.
- Glass-only fixes when the frame is sound
- Structure checked before quoting
- Heritage permit explained first
Know the house
Bay or bow: what you have
Bay
Usually three units: a wide centre, often fixed, between two angled side windows that open. Front rooms of Markham houses from the 1980s to the 2000s often have one.
Bow
Four or more similar units in a gentle curve. More joints and more glass mean more weight on the supports, so sagging tends to show sooner.
Heritage bay
On older houses, the bay is part of the architecture. The City's architectural styles guide lists bay windows among the features of Queen Anne Revival homes built from the 1880s to 1915.
One lite at a time
Replacing glass in one lite of a bay
Each window in a bay has its own sealed unit, or lite. If only the centre has fogged, it's replaced while the sides, frame and trim stay; our foggy window page explains why seals fail.
The care goes into matching tint, coating and grilles across the row. A large centre is handled like any big picture window; a shaped unit above is covered under arched and transom glass.
Beyond the glass
Sagging, drafts and a cold seat: the structure around the glass
Many bay complaints aren't about the glass. The pro will say which fixes are theirs and which need another trade.
Sagging
A gap above the trim or a seat sloping outward can mean the cables or brackets have let go. They can be reset or added.
Drafts at the corners
When the insulated posts between units, called mullions, lose their seal, cold air gets in though the glass is fine.
A cold seat
A poorly insulated platform under the seat board stays cold whatever glass is above it.
Water from above
Stains on the head board usually point to flashing on the small roof, which can be a roofer's job.
The whole unit
Full replacement: what's involved
When the frames fail or several units fog at once, a new bay can beat a string of repairs. The old assembly comes out whole, the supports are checked, and the new bay is set, insulated, flashed and trimmed. Our replacement windows page explains retrofit and full-frame work.
Markham needs no building permit for a same-size replacement, per its permit page; ask before changing the size or shape. A complete ENERGY STAR replacement may count toward Ontario's Home Renovation Savings rebate; new glass alone does not.
What affects the quote
Why bay quotes vary so much
A bay can be a one-unit glass job or a small building project. The quote depends on:
- One sealed unit, several, or the whole assembly
- Grilles, tint and coatings to match
- The condition of the supports, seat platform and head board
- Interior trim, and whether it can be saved
Photograph the bay from outside and inside, plus any corner that's drafty or stained.
Heritage houses
Bays on heritage houses
Every property in Markham's four heritage conservation districts, Unionville, Markham Village, Thornhill and Buttonville, needs a heritage permit before exterior changes, windows included. The district plans ask for repair of original frames and sash first, and replacement only in matching material and proportion.
For a Queen Anne Revival bay, that usually means repairing the wood sash, not fitting a vinyl bay. Our heritage district guide covers the permit and the City's 2026 heritage grant, which can help pay to repair original windows.
Questions
Bay and bow window questions
Explore your options
Related window work
Local pros work on bay and bow windows across Markham, including Unionville, Markham Village, Angus Glen and Box Grove.
Photograph the whole bay, inside and out
Add a close-up of whatever bothers you: a fogged pane, a gap in the trim, a cold corner. We pass it to a local pro who works on bays and follows up with a written quote.