What a casement window actually is
The sash, the opening part, is hinged along one edge and swings outward on a stay. That single hinge line is what separates it from a tilt and turn, which hinges on two edges, or a sash window, which slides vertically.
Because the whole sash swings clear of the frame, you get full ventilation from even a modest opener, which is why casements suit kitchens and bathrooms as well as bedrooms.
Opening configurations you will be asked to choose between
Side hung is the standard arrangement, hinged down one vertical edge and opening outward. Top hung windows hinge along the top and open outward from the bottom, useful above worktops or where a side hung sash would clash with a path or a bin store.
Fixed lights do not open at all and cost less, which is why a wide window is often specified as one opener flanked by two fixed panes rather than three openers nobody uses. A dummy sash looks exactly like an opener from the street but is sealed shut, used to keep a symmetrical elevation on a house where only some rooms need ventilation.
- Side hung, hinged on a vertical edge, the everyday choice
- Top hung, hinged along the top, good for hard to reach spots
- Fixed light, no opener, cheaper and thermally tighter
- Dummy sash, decorative only, matches the look without the function
Profile chambers and reinforcement
Modern uPVC frames are extruded with several internal chambers rather than being a solid tube. Each chamber traps still air, which is what actually slows heat loss, so a five or six chamber profile generally outperforms a two or three chamber one for the same wall thickness.
Wider spans and taller sashes need galvanised steel reinforcement inserted into the chambers to stop the frame flexing in wind or under its own weight. A reputable installer will reinforce based on the opening size, not fit the same bar everywhere to save time.
Hinges: friction stay, easy clean and egress
A friction stay hinge holds the sash open at any angle and resists wind pushing it shut, which is the standard fitting on a side hung casement. An easy clean hinge lets the sash rotate almost 180 degrees so you can wipe the outside glass from inside, useful upstairs or anywhere access outside is awkward.
Bedroom windows generally need an egress hinge, which opens wide enough and quickly enough to meet Building Regulations escape requirements, a detail worth checking rather than assuming.
Get a fitted price for your casements
Tell us your opening sizes and we will quote standard or flush casements, fully fitted, with no pressure to upgrade.
Glazing and Window Energy Ratings
The glass unit does most of the thermal work: a warm edge spacer bar, an argon filled cavity and a low-E coating together bring the U-value down, and the combined performance is shown on the Window Energy Rating label from A++ down to lower bands. Ask to see the WER for the specific unit quoted, not a generic figure from a brochure.
Flush casement vs standard casement
A standard casement sits proud of the outer frame, visibly stepped, which is the cheaper and more common look. A flush casement closes level with the frame, echoing a timber window, and suits period elevations or conservation style streets where a stepped profile looks wrong.
The flush look costs more to manufacture because the sash and frame are cut to sit flush rather than overlap, which is reflected in our from-price of £520 against £450 for standard.
| Style | From price, fully fitted |
|---|---|
| Standard casement | £450 |
| Flush casement | £520 |
| Triple glazed casement | £610 |
Sizes, trickle vents and Part F
Building Regulations Part F requires background ventilation in habitable rooms, usually met with a trickle vent built into the head of the frame. If you are replacing like for like this is often required even when the old window did not have one, since the regulation applies to the new installation.
Standard casement sizes are fairly flexible because the profile is extruded rather than cast, but very wide single sashes need extra reinforcement or splitting into two openers with a mullion, which a proper survey will flag before manufacture rather than on site.
Security hardware: espagnolette locks and cylinders
A casement window is normally locked by an espagnolette mechanism, a single handle action that drives locking points along the full height of the sash into keeps on the frame, rather than a single point catch. More locking points spread the load if anyone tries to force the sash, which is why multi point locking is the standard on every casement we fit rather than an optional extra.
Where the window includes a cylinder, for example on a handle with a key, a TS007 3 star rated cylinder resists the drilling and snapping attacks that older cylinders were vulnerable to. Pairing a 3 star cylinder with 2 star hardware, or checking the handle itself carries a security rating, gives the same overall protection at lower cost than replacing both with 3 star parts.