Bay vs Bow Windows

A bay window is angular — typically three panels forming a trapezoid, with the central panel wider than the two returns. A bow window is curved — usually four or five equal panels forming a gentle arc. Bay = angular; bow = round-ish.

Bay windows are quintessentially Edwardian and 1930s British suburban. Bow windows read Georgian or American colonial. On a UK street of 1930s semis, a bow window replacement looks out of period. On a Georgian townhouse or a modern build seeking a soft curve, a bow can work beautifully.

Bay windows are load-bearing when they're original — the return walls carry the roof above. Any replacement must maintain that structural support. Bow windows are usually non-load-bearing overlays. Ask a surveyor to confirm before ordering — the wrong assumption is expensive to fix.

Bay windows can have a small lead-clad or tiled bay roof, or an integrated fibreglass roof. Bow windows almost always use an integrated GRP or lead roof due to the curved geometry. The roof detailing is often what dates a poor replacement — get it right and the bay looks period-correct.

Bay replacements start around £3,500 for a standard 3-panel bay in uPVC and rise to £8,000+ for aluminium or timber. Bow windows cost 15–25% more due to more panels and more complex roof geometry. Both require structural sign-off and, in conservation areas, planning consideration.