Casement Windows Explained: A Complete Guide

Top hung versus side hung

The two main hinge arrangements are top hung and side hung. A top hung casement is hinged along the top edge and opens outward from the bottom, similar to an awning, which makes it a useful choice for a window you want open slightly even during light rain, since the top acts as a small canopy. A side hung casement is hinged down one side and swings open like a door, which usually allows for a larger opening area and easier cleaning of the outside face from indoors.

Many houses use a mix of both within the same window frame, for example a side hung opening light next to a fixed pane, with a top hung vent above for background ventilation.

Flush casements

A flush casement is a specific style where the opening sash sits flush with the surrounding frame rather than proud of it, giving a flatter, more traditional appearance that is often chosen to suit period properties or conservation areas where a more authentic timber-look profile is wanted. Flush casements are available in uPVC, aluminium and timber, so the traditional look does not necessarily mean traditional maintenance.

Fixed lights and dummy sashes

Not every section of a casement window needs to open. A fixed light is a pane of glass set permanently into the frame with no hinge, often used where ventilation is not needed or where matching a symmetrical appearance matters more than function, such as either side of a front door.

A dummy sash takes this a step further, it looks like an opening casement from the outside, complete with a visible frame line and sometimes even hardware, but is actually fixed shut. This is mainly a cosmetic choice, used to keep a symmetrical multi-pane appearance across a wide window while only some sections genuinely open.

Restrictors and egress requirements

Window restrictors limit how far a casement can open, which is particularly relevant for upper floor windows in households with young children, since they prevent a window opening wide enough for a child to fall through while still allowing ventilation. Most restrictors can be temporarily released by an adult, so they do not compromise your ability to use the window as an emergency escape route.

Building regulations require certain rooms, particularly bedrooms, to have at least one window that provides an adequate means of escape in an emergency, with minimum dimensions for the opening. A good installer will factor this into the design of your casement windows rather than treating restrictors and escape requirements as an afterthought.

• Restrictors limit opening width, usually to around 100mm, for child safety
• Escape windows need a minimum clear opening area and height, particularly in bedrooms
• Restrictors should be easily releasable by an adult without a key in an emergency

Glazing options

Casement windows accept the full range of modern glazing specifications, from standard double glazing through to acoustic laminated glass for noise reduction and triple glazing for extra thermal performance. Because the sash opens as a single hinged unit, casements are also well suited to decorative glazing bar designs, Georgian bar effects, or leaded patterns if you want a more traditional appearance.

Cleaning and maintenance

Side hung casements are generally the easiest window style to clean from inside the house, since the whole sash swings open to give access to the outer glass face. Top hung casements can be slightly less convenient for cleaning the top corners depending on how far they open. Ongoing maintenance is minimal, mainly keeping hinges and locks lubricated and drainage channels clear, alongside an occasional wipe down of the frame.

Where casement windows suit best

Casement windows work well on almost any property type, which is a large part of why they are the default choice for most UK homes. Flush casements suit period terraces and conservation areas where a traditional look matters, while standard casements in uPVC or aluminium suit modern extensions, bungalows and semis equally well. Where a wide expanse of glass is wanted, combining fixed lights with opening casements often gives the best balance of light, ventilation and cost.