Bay windows and bow windows: the difference
A bay window is usually three units: a large fixed window in the middle and two narrower windows on the sides, set at an angle to the wall. The side windows often open. A bow window uses four or more equal panels in a gentle curve and sticks out less sharply. Both make a shallow alcove with a seat or shelf, and both are replaced the same basic way.
What bay window replacement involves
Before anything is ordered, we look at the parts that keep a bay in place and keep water out:
- The seat and head boards, the flat panels at the bottom and top of the unit, checked for rot and water stains
- The roof over the bay, whether it's a small shingled roof or flashing tucked under the eave
- The support: cables to the wall framing above, brackets underneath, or a framed bump-out to the ground
On install day the old unit comes out and the new one is set, supported and flashed into the wall and roof. The space under the seat and above the head board gets insulated, a spot older installs often skipped. Then the interior trim and seat are finished.
Signs a bay or bow window needs replacing
- Gaps opening at the top corners, or a seat that slopes away from the wall
- Water stains on the ceiling inside the bay or on the seat board
- Soft wood under the seat or along the bottom of the unit
- A seat that's cold to the touch all winter
- Fog between the panes on one or more sections
- Side windows that stick, won't lock, or let air in
Why bay windows fail
A bay hangs its whole weight off the wall. Over the years support cables loosen and brackets rust, and the unit starts to drop at the outside edge. The little roof and its flashing are the most common leak point, and once water gets behind the trim it finds the seat and head boards. On top of that, many older bays had little or no insulation above and below, so the alcove runs cold in winter and hot in summer.
Same style, or something different
Most people replace like for like, with better glass and a tighter install. You don't have to, though. A bay can become a bow if the opening width suits it, side windows can switch from double-hung to casement, or the center window can be made larger. Going back to a flat wall of windows is possible but means framing and siding work, so it costs more.
What affects the cost of a bay or bow window
- Overall size and number of panels
- Which panels open and which are fixed
- The glass package
- The roof over the unit and how it ties into the house
- How the unit is supported
- Rot repair at the seat, head board or wall framing
- Interior finish on the seat and head boards, and any siding patching outside
Bay and bow windows cost well more than a standard window of the same width. The cost page covers what goes into a quote.