Double glazing styles are usually presented as a matter of taste, and they are, but they are also a pricing decision. The style of a window determines how many moving parts it has, what hardware hangs and locks it, how it is made at the factory and how long it takes to fit. That is why a straightforward change of style across a whole house can move a quote further than a change of glass specification, and why it is worth settling style before you start comparing numbers.
Casement is the default, and the cheapest place to start
A casement window is hinged at the side or the top and opens outwards, and it is what most British replacement windows are. Its price is driven by how the opening is divided: a single large fixed pane is the cheapest arrangement, and every opening sash added to the frame brings hinges, a locking mechanism, a handle and a seal. This is the reason a window firm asks how many of your existing sashes actually open before it quotes, and the reason keeping fixed lights fixed is the easiest saving in any specification.
Flush casement costs more because it is made differently
A flush casement sits level with the frame when closed rather than sitting proudly on it, which is how timber windows on older houses were traditionally made. Reproducing that in uPVC or aluminium needs a different profile and different tooling, so it is a dearer product rather than a finish option. It is a common choice in conservation areas and on period properties where a standard stormproof casement looks wrong, and it is worth pricing it separately rather than assuming it is a small upgrade.
Tilt and turn buys cleaning access and pays for hardware
A tilt and turn window tilts inwards at the top for ventilation and swings fully inwards for cleaning, which makes it useful above ground level where the outside face is hard to reach. All of that lives in the hardware, which is more complex and more expensive than a casement's, and the window opens into the room, so it changes where furniture and curtains can go. It is a sensible choice for flats and upper storeys and an expensive one applied to a whole house without reason.
Bays and bows are structural, not decorative
A bay projects from the wall in flat sections at angles, a bow curves in shallower ones, and both carry whatever is above them. Replacing them means dealing with that load, either through a structural head or a corner post system designed for it, and that work is priced on top of the windows themselves. This is why a bay is never one window in a quote and why the cheapest way to get a bay wrong is to let somebody price it as though it were.
Sash windows are their own decision
Vertical sliding sash windows are the traditional pattern across much of British housing, and modern replacements reproduce the movement with spiral balances or weights. They are more expensive than casements in every material, the detailing matters a great deal to how a period house looks, and in a conservation area or on a listed building what you may fit is not entirely your choice. If your house has them, price sash replacements against sash repair before assuming replacement is the route.
Conservation windows, and what a conservation area or a listing changes
In a conservation area the local authority can restrict what replaces a window, and an Article 4 direction removes the permitted development right to change them at all without applying. On a listed building the windows are part of the listing and altering them needs listed building consent, whoever fits them. What the authority usually wants is the original pattern kept: the same opening style, the same sight lines, timber where the house had timber, and no trickle vents cut across a historic frame where another route exists. The two answers that most often get consent are a slim profile double glazed unit in a frame made to the original section, and secondary glazing behind the existing window, which alters nothing outside. Ask the conservation officer before ordering rather than after, and treat any installer who says their certification covers it as somebody who has not read the designation: a competent person certificate covers the building regulations and has nothing to do with planning consent.
Questions people ask about double glazing styles
Can I mix styles across one house?
You can, and it is common where a front elevation is period and a rear extension is modern. Within a single elevation, mixing usually reads as an accident rather than a decision, so it is worth drawing the front of the house before choosing.
Does style affect the energy performance?
Indirectly. More opening sashes mean more seals and more frame relative to glass, which changes the whole window performance even with identical glass. The difference is real but smaller than the difference between frame materials.
Are period style windows allowed everywhere?
The question is usually the other way round: in conservation areas and listed buildings the authority may require a particular style, material or opening pattern. Ask the local authority before ordering rather than after.