There’s a lot about casement windows that makes them unique. They can be manufactured in a range of materials and to various sizes and budgets, with different style options available. And they are among the most popular window types for UK consumers.

In this post, we will cover everything you need to know, including how they work and their advantages and disadvantages for your property.

What are Casement Windows?

A casement window attaches to its frame via a side-mounted hinge. This means they can swing open in the same way a door would, though they are also available as tilt-and-turn windows.

Casements open outwards in virtually every case, using a small mechanical crank or handle situated on the opposite side to the hinge. The crank or handle usually functions as a latching mechanism to lock the window shut and secure it in place when open. Casement windows:

Different Types of Casement Windows

There are actually a few variations on the way casement windows are presented. Here are the different types you may encounter:

What Are the Different Components of a Casement Window?

A casement window is made up of multiple parts. They may not always be in the same place, but they will all be there in virtually every casement window. Please note that, in addition to the following, a casement window may include Georgian or Astragal bars as decorative features.

The Frame

This holds the casement window in place. It is composed of a head and a sill that run along the top and bottom, combined with a vertical jamb on either side. The sill (or cill) is usually slanted to direct water away from the building.

Mullion and Transom

These are strips of uPVC, timber or aluminium that supports the structure and divides separate window units. The mullion is a vertical strip, while the transom is a horizontal one. Some windows will have both, while others will only have one or neither.


This is the part of the window that opens. It secures the glazing in place and is the component of the window that you will interact with. A locking mechanism is located on the casement jamb for securing the window in a closed or open position.

Trickle Vent

Situated at the top of the window, trickle vents have a grill on the outside and a closing vent on the inside. They allow moisture to evaporate and leave the building to help prevent condensation on window interiors. You can learn more about trickle vent in our informative article Trickle Vent Regulations Explained.

What Are the Pros and Cons of Casement Windows?

There is lots to love about casement windows, but there are also some limitations that are worth thinking about. Let’s take a look at the strengths and weaknesses of these window types.

Here’s what makes casement windows great:

Casement Windows Disadvantages

There is one particular limitation to be mindful of with casement windows.

They are limited by the size of the opening panel. The weight of the glass means the opening panel hinge must support the window, so it can only be built up to a particular maximum size. This is why the central section of a bay window is typically fixed and cannot be opened. Casement windows may also be vulnerable to damage when open in strong winds or heavy rainfall, and installation and repairs can be complicated.

Despite their minor limitations, the design versatility means there is a configuration to work for virtually any property.

How do Casements Compare with Other Window Types?

There are some key differences that differentiate casement windows from other window types.

Casement Windows vs Sash Windows

Sash windows open by sliding one panel across the other. This means that only one window can be open at any time, so you get less ventilation that you would with a casement window. Traditional sash windows may be less efficient that casements as they don’t have the same latch or watertight seal. However, they can be designed to be very energy efficient.

Casement Windows vs Jalousie Windows

Jalousie windows consist of glass slats across the frame which open and shut like blinds. They can be a unique focal point in a building’s design, but they are less durable than casements as the smaller slats can be broken. They also lack the energy efficiency of casements as they may still allow cold air into the building when they are shut.

Casement Windows vs Fixed Windows

Fixed or ‘picture windows’ differ from casements in that they cannot be opened. They may come in different styles, like an arch with a rounded top. Fixed windows are often paired with casements to allow ventilation in a room.

Final Thoughts

Casement windows offer the best balance between aesthetic appeal, functional merit, durability and affordability. It is no surprise they are the most popular type of window on the market, and they should definitely be on your radar if you are looking to get new windows for any type of building.

Why choose Eco Thermal Design for your new windows?

Eco Thermal Design has transformed countless homes across Barnsley, Sheffield and other areas of South Yorkshire. We are experts when it comes to windows and can help you find the right windows for your home. We manufacturer our windows in our factory in Barnsley, and only work with quality brands such as KömmerlingSchucoSheerline and Origin. We also offer Residence Collection windows, perfectly suited for period properties.

Our expert team can help you decide on the right window for your home, and our team of fitters can complete their work to the highest standards, causing you minimal disruption along the way. We’re proud of the quality of our products, work and people, which is echoed by our customers in our Which Trusted Trader reviews.

If you would like to speak to one of our window experts or get a quote, you can contact us here or give us a call on 0800 009 6241.

What Our Customers Say

“Quality products are only as good as the team that fit them and in our case both the product and the fitters resulted in a first class and professional installation. Respectful of our home and tidied up at the end of each day….Thank You”
Les Finucane

“Excellent service from Eco Thermal again. Would recommend to anyone. Also good to have a local firm that you can trust.”
Ross Duguid

“Very happy with the whole process and of course the finished installation.”
Michael Senior

You can also read our reviews on Which Trusted Trader where we are rated five stars.