Oriel Windows – Specifying Tips & Advice For Architects

When it comes to ‘wow factor’ in the world of structural glazing, oriel windows stand out – literally, as well as figuratively. These load-bearing glazed protrusions are often used as window seats, offering a snug space to enjoy a coffee and a good book while enjoying all the benefits of natural light and a connection with the outdoors.  



20 Apr 2022


Simon McAuliffe

Oriel windows offer a wealth of potential, conferring both aesthetic and practical benefits; but when it comes to specifying an oriel window, architects are faced with a range of challenges and factors to consider. Having worked on many of these projects over our four decades in the industry, we thought we’d share a few tips that we’ve picked up along the way…

What is an oriel window?


Simply put, an oriel window is a window that projects from the facade of a building but does not reach the ground floor. With a solid base, oriel windows are often used as window seats, offering an idyllic and enviable reading and relaxation corner.


Oriel windows aren’t something new. They have been used in architecture since the Middle Ages in Europe and the Middle East, although their aesthetic qualities and design trends have developed enormously. Since the evolution of structural glass, modern oriel windows have taken on a  striking, geometric style, showcasing just how versatile modern glazing can be. 


Is an oriel window the same as a bay window?

Both an oriel window and a bay window project outward from the main structure of a building, but the main difference is that oriel windows are supported by brackets or corbels and are often found on upper stories of buildings, whereas bay windows typically extend from the ground floor and are supported by the building itself.


Oriel window construction details – glass specifications 


In terms of oriel window construction details, the specification for the glazing itself is a crucial consideration – both from a visual and practical perspective. Safety and thermal performance are two key factors when choosing a glass specification, along with the structural context for the location of the window:


Thermal performance

 Thermal performance is a key consideration and the coating on the glass specified according to the location and orientation of the glass should be considered in the glass specification. Specifically, for South or West-facing windows, a solar control coating may be necessary to prevent undesirable heat build-up. 

Conversely, for North-facing installations, solar gain can ensure energy retention from sunlight, even on a cold winter morning!


Toughened and Laminated Glazing

Horizontal, overhead glazing for the top of oriel windows should always be laminated internally for safety reasons- all overhead glazing will incorporate extra stiff state-of-the-art interlayers. This is a safety must-have, to ensure protection for inhabitants if anything were to fall on the glazing, keeping the glass sheet “intact” even if the individual layers of glass within the laminate are broken. 


oriel windows

Low-iron Glazing

Most of our oriel windows are load -bearing, allowing them to be used as a seat, however, this also means thicker glass panels. As such, low-iron glass should be used to ensure better transparency, and a clearer visual finish (reduction of the green tint that thicker glazing can suffer from).


Other glazing options

Fortunately, with the above points factored in, other options for glass can be explored relatively freely – while not everything works well in practice, our designers are experienced enough to be able to make most requirements for the glass specification itself work comfortably. This can include ideas like photovoltaic switchable glass, additional protection such as low maintenance hydrophobic coatings (we recommend Enduroshield), and more. 


Design process for an oriel window


From the perspective of the glazing specialist, the process for designing and engineering an oriel window is a relatively straightforward one – once the cantilevered box frame is designed for the ‘seat’, and the glass specification is determined, it’s mainly a question of how to finish the oriel window.  

But there are a few key things to be aware of during the design process:


Get the detailing done early

 As with all aspects of architecture, the earlier things can be detailed, the better. Due to the load-bearing properties and structural nature of oriel windows generally, the glazing specialist will need to provide the engineer with plenty of input as early as possible.

Designing an oriel window is a collaborative effort between architect, engineer, and glazier – there needs to be clarity on detailing the interface between the oriel window and the wall, so having the conversation early on will ensure avoidable hurdles won’t crop up during installation. 


Think in ratios

With oriel windows, the nature of structural glazing as a load-bearing material means that the design needs to be approached in ratios. Simply put, the taller the window, the deeper the protrusion of the base will need to be, to ensure the glass isn’t poorly supported or flimsy. At Cantifix, we generally work to a 1:10 ratio with toughened glass, so if the window is going to be 2 metres tall, the protrusion should be a minimum of 200mm.


Factor in the characteristics of the building

The glass specification will need to adapt to the structure the window will be built into, so your glazing specialist will need a clear picture of what’s currently in place. Detailing will need to be adapted – in the case of new builds, this is usually straightforward, as we can incorporate channels easily within the new build up; if the building is older, this may be different as old buildings tend not to be squared off or straight, and your specialist will need to know what kind of finishes and depths to work to and fix into.



Aesthetic considerations for oriel windows

 For most clients, aesthetics will be the most important factor in opting for an oriel window. From a visual perspective, the solutions can be enormously versatile and impactful, and depending on the glass specification used, can be designed to suit a variety of different styles.

There are limits (for instance, while UV-bonded ‘invisible’ corners could work in theory, in practice, this could only work on the vertical joints, so thought would need to be given to all junctions for appearance – at The Newt in Somerset we used glass spacer bars in their oriel window instead of the usual metal spacers for a “frameless” appearance) but Cantifix are always able to advise on specifics and will work as closely to your desired appearance as is structurally possible. 

While the aesthetics for the glass itself are flexible, with minimal glazing and other design styles all available, one of the biggest questions is around the base of the oriel window; you’ll need a clear idea of how you want this to look (although of course our specialists can happily recommend various solutions). 

For example, a popular option is to include back-painted glass panels, which oversail the solid base, creating the coveted ‘all-glass’ appearance many homeowners strive for. 


Benefits of Oriel windows


Oriel windows offer a wealth of practical and visual benefits to the homeowner, and it’s not surprising to see how popular they’ve become. They increase usable space, maximise beneficial natural light, and can actively contribute to interior climate and ambience – maintaining a pleasant temperature in both summer and winter, whatever the weather. 

They can offer a pleasant ‘cubby’ space for reading, home working, or simply enjoying a morning coffee, and they provide a tangible physical link between an interior and exterior environment, seamlessly connecting the indoors and outdoors. 


Does an oriel window require planning permission?


An oriel window is considered to be an extension of the existing structure, rather than a separate structure in its own right. Therefore, if you are replacing an existing oriel window with one that utilises modern materials (for example), you do not need planning permission. Likewise, if you are adding an oriel window to the rear or side of a property, you usually do not need planning permission. If, on the other hand, your oriel window extension will be at the front of your building, you do need to apply for planning permission. These things will, of course, depend on how far the oriel window protrudes and whether your property sits within a conservation area.


Final thoughts


When it comes to glass specifications for oriel windows, considering everything mentioned will ensure that your chosen glazing specialist has plenty to work with, to efficiently and effectively detail the glazing. Every project is different , so at Cantifix we cannot  do off the shelf ’ solutions. There will still need to be conversations around specifics – but by following the advice and tips above, and considering these universally-relevant factors well in advance, you can ensure a smooth design and installation process, with phenomenal results for your clients. 


If you’d like to know more, or would like to speak to Cantifix about your own project, our experts are always happy to chat. Simply head over to our contact page, fill in the form, and we’ll be in touch!