Home > Four considerations when specifying external blinds
A side view of the Zip Guided External Roller Blinds on an office block

Four considerations when specifying external blinds

By: Oli Birch Category: External Blinds

While they’re regularly specified across Europe, external blinds have yet to really become a consideration for many projects in the UK.

However, this is starting to change, with architects beginning to show significant interest in these products.

With a myriad of systems and configurations available, we’ve identified four key points specifiers should consider when deciding on the best external blind for their project.

Basic functionalities – What exactly do you need the external blinds for?

While it may seem obvious, answering this question will give architects a great idea of the type of external blinds they need. But answering this question requires significant thought for three sub-questions too.

Firstly, is glare control the main aim or does the project require a dim-out option? The former is likely to be more relevant for commercial projects, where occupants will need sufficient protection from glare to ensure they’re not straining to use computer screens at work. Meanwhile, multi-dwelling units may need greater dim-out qualities from external blinds to provide darkness for bedrooms.

Zip Guided External Roller Blinds

This leads nicely on to the next question: is occupant comfort or energy efficiency the main aim of the project? If thermal control or security is the priority, an external shutter offers the highest level of protection against the impact of solar radiation and is arguably the best-performing external blind for this requirement. However, an external roller shutter would also compromise the view to the outside when deployed.

Finally, do you want high-performance external blinds or are aesthetics of more importance? Often, the top tier performing systems for light and thermal control result in a sacrifice in aesthetics. For instance, external roller shutters are the bulkiest option and do not have a greater range of finishes compared to an external roller blind.

Level of control

Every external blind system has a specific wind speed threshold at which it is no longer safe to be deployed. Therefore, it’s of paramount importance to have a basic level of automation to retract the external system in the event of this threshold being reached.

While the threshold varies between different systems, as some external blinds are more robust than others, the highest performing systems can operate in speeds of up to 25m/s (Beaufort 10).

The average UK wind speed in m/s

This diagram highlights the average wind speed data across the UK, serving as an initial guide for which systems may be most suitable, depending on the location of the project. We would always recommend specifying external blinds with a higher wind speed threshold than the geographical average.

However, when specifying external blinds for high-rise buildings or skyscrapers, wind speeds may differ on higher floors compared to lower levels. Therefore, this diagram should only serve as a rough approximation.

Additional features like occupancy sensors, time clock functionality or solar tracking can be added to enhance the level of control and performance of the system. We discuss this more in our RIBA-approved CPD, Introducing the Benefits of an Automated Shading System.

Furthermore, it’s important to remember that additional features like this can be added retrospectively, as long as the backbone of the smart system is installed initially.

Fixing options

The third key consideration when specifying external blinds is the fixing options.

Understandably, a big concern for architects and designers is identifying the level of interference that external blinds can have on a building façade.

If external shading is required for a retrofit project, there is often little choice other than an exposed fixing direct to the façade. And, occasionally, this can be hindered by restrictions on penetrating the façade or masonry.

Hence, an ideal solution is incorporating external blinds at the design stage of a project. This gives architects ample opportunity to recess the fixing and achieve the façade aesthetics they’re after.

A close up image of the Recessed External Venetian Blind built into the façade

With many external blinds, there will be a requirement for fixing along the sides of a window or opening.

This could be a complete side channel retaining the edge of the fabric or fixing points for side-guide rods/wires. Therefore, it’s important to consider how and where these fixings will be placed, alongside the consideration for the headbox.

Seamlessly integrating external blinds into the façade can often mean working alongside façade contractors, window fitters or builders at an early stage to ensure a smooth delivery process.


Finally, an additional consideration needs to be made for how an external blind will be maintained once installed.

One of the main issues regarding maintenance is around gaining access to the motor and shading elements. In some cases, an internal access panel can be incorporated in the design to allow easy and safe access to the device from the inside of the building.

However, depending on the way in which the windows open, you may be able to gain access to the system from inside the building without the need for a panel. This relies on sufficient strong points for an operative to anchor to.

If internal access is not an option, boom lifts, cherry pickers or abseiling are the three main alternatives for external access. This does make the operation slightly more challenging, though, as in some cases road closures may be required for safe operation.

Furthermore, there is a greater challenge in maintaining high-rise buildings in this way, so we would always recommend an internal access panel where accessible.

If you’d like to discuss external blinds for your project, please contact us here and our expert team will be in touch. Alternatively, you can book in for our RIBA-approved CPD, External Shading Systems, to learn more about the systems.

    • Max. file size: 512 MB.
    • This field is for validation purposes and should be left unchanged.