The practical difference between square, angled and curved bays, and the questions a surveyor should ask before quoting.
Short answer: a bay window uses three or more flat frames set at an angle (or square) to the wall, while a bow window uses four or more narrower frames arranged in a gentle curve. Both project outwards, both add floor space and light, and the right choice usually follows the shape of the opening you already have rather than taste alone.
Replacing a bay is a bigger job than swapping a flat window because the frames often carry part of the load from the roof or brickwork above. That structural question, far more than the glass, is what separates a sound quote from a risky one.
We fit three configurations. Square box bays give clean, modern lines. Angled bays, usually at around 45 degrees, suit traditional and Edwardian frontages. Curved bow windows create a sweeping line and look best on rounder openings or where a softer outline is wanted.
Changing from one shape to another is possible but may involve new roofing over the projection, new sills and in some cases alterations to the brickwork. Keeping the existing footprint is nearly always the simpler route.
On many older houses the original timber bay frames were built to support the roof of the bay or even the wall above. When those frames come out, the load has to go somewhere. Most installers deal with this using steel bay poles hidden inside the new frame couplers, or by confirming a lintel is already in place.
A good survey checks for signs of movement, looks at what sits above the bay and decides whether support is needed before the price is fixed. If a quote does not mention it at all, ask.
Because every bay is a set of linked frames, several choices stack up:
A bay has more glass and more joints than a flat window, so it can be a noticeable source of heat loss when the old units fail. Modern A-rated glazing brings a bay into line with any other window in the house, provided the couplers between frames are properly sealed and insulated.
uPVC is the most common choice and suits most period and modern homes. Aluminium allows slimmer sightlines and more glass on each facet, which many people prefer on contemporary properties or where a dark colour such as anthracite grey is planned.
We measure every facet, check the structure above and give you a fixed quote with no obligation. We beat any like-for-like quote.
Not quite. A bow window is a type of bay made from more, narrower frames arranged in a curve, while a standard bay uses fewer flat frames at an angle or square to the wall.
Replacing like for like is usually permitted development on a house, but listed buildings, flats and some conservation areas have extra rules. Check with your council if any of those apply.
Sometimes. It depends on what the original frames were carrying. A surveyor should check this before the price is fixed, and support is usually hidden inside the new frame joints.
Yes, any facet can have an opener, although each one adds to the cost. Many people choose openers on the two side facets and a fixed centre pane.