Getting the Light Right: Designing with windows in mind

When it comes to designing windows for a residential building, many people think that the bigger the window the better – that it invites more natural light into apartments and offers more opportunities for ventilation. However, although this is in part true, there are many more factors to consider – both in terms of practicality for installation and in meeting all regulations and safety requirements.

Daylight, ventilation and acoustics

There are three keys things designers and architects should take into consideration when they design for residential buildings.

The first is daylight and the need to encourage as much natural light as possible into a building. However, it’s not just a case of putting in huge windows. If, for instance, the window is north facing, you have to consider the thermal performance of that huge window. If the thermal performance is enhanced with triple glazing, imagine the implications of a very heavy window on the overall weight of the building and the complexities of installation and maintenance. Slim frames will naturally allow more glass to bring in light and the orientation of the building can inform the energy balance needed in terms of solar control the type of glazing needed.

The second key consideration is ventilation. There are natural and mechanical ways of ventilating a building and depending on what has been specified. This has an impact on the design of the windows also. Naturally, vented buildings will need window designs that allow free air through windows, including trickle vents that can be opened when the window is shut.

Thirdly, acoustics is key to making apartments and common areas comfortable. Nobody wants a noisy living area, so architects need to look at the difference between the inside and outside noise levels to determine an appropriate window to install.

Take all of these aspects into consideration and it will give architects and designers a good understanding of what impact it can have on window and door size and functions. You can design in as much light as you can for the project, but what needs scrutinising is whether all of the above can be achieved to specification requirements. It comes down to a delicate balancing act of daylight, ventilation and acoustics to achieve both comfort and aesthetics.

Added to this, we also need to consider the amount of privacy needed for residents and the impact that has on design.

Early engagement

The job of the supplier is not just to give the client exactly what they want – that could be irresponsible. A lot of the work is about managing expectations and informing them of all the other requirements needed beyond aesthetics.

It’s crucial, therefore, to get involved as early as possible – ideally at RIBA stage two or three. Although it can be difficult at times, when it is possible, suppliers can influence the core designs before they go out to planning, saving much wasted time and money. Unfortunately, if suppliers aren’t involved in a project early on, and it’s gone through the initial stages of planning and concept design, architects can be including very large windows in areas that need significant specification requirements. This increases the level of complexity of design and manufacture. A requirement, for example, could be acoustic for example, and large windows and acoustics don’t really marry.

It’s important to work with architects early to design something that is workable, in budget and in accordance with all the relevant regulations. Our role is to ask pertinent questions as part of our expertise on acoustics, U Values and solar control, which then informs and creates a detailed specification fit for the project.

Early engagement can also establish clarity on whose role it is to establish the U-value standards on a residential building. Often architects will say it is the monitoring and evaluation team, and the monitoring and evaluation team will say that it is the architects’ task to determine the U-value and any improvement over building regulations. Either way, the sooner this is established, the better for the project as misunderstandings can very easily be passed from project to project. Should specifications be cut and pasted to the next job, for example, they could include an out-of-date regulation or standard or something that would be inappropriate for use given the rest of the specification.

Industry shifts affect window manufacture

Including specialist input early on is key for window manufacturers, so we can offer insights and data really early on. Suppliers are able to take the windows that have been planned and check for size, function and performance and determine the different values for each window throughout the building.

There has been a shift on the industry in the last few years towards use of greater glass technology to control the internal climate. This in turn has an impact on light transmittance (LT value). Increasingly, more glass is being incorporated into the external envelope, enabling more light and airy apartments. This of course is a big selling factor, but the impact on the heat which comes through the glass and on the light transmittance through the windows (both inside-out and outside-in) can be seen in both the complexity of design and the overall costs incurred. Therefore, it’s imperative to have a detailed understanding of the performance requirements around the whole building.

Factors like these have an impact on performance. And performance changes, depending on height. For example, higher up the building, the acoustic performance changes. A dual aspect building has specific requirements also. So, all of these issues should be regular topics of conversation throughout the project, not just at end user stage, when they become a problem.

Guidance for architects

It’s also important for architects to consider Part M compliance, along with cleaning strategy, and any security requirements such as Part Q or SBD/PAS 24 – and the impact that these can have on opening functions, handle heights and positionings from FFL, along with clear openings and thresholds for doors. This whilst keeping in mind the impact of third-party insurers also, as their requirements can further impact product selection, design & installation.

Remember to have a clear cleaning strategy too, and how any particular window can be cleaned thoroughly. Can it be cleaned internally or is extra equipment needed on the building if they are to be cleaned externally?

Good architects look at their design in terms of buildability. The viability of a project is determined by the level of engagement they have with experts and suppliers. That way a perfect balance between aesthetics, practicality and comfort can be struck.

This article is based on an interview with Neil Edwards, Window Specification Consultant and Ollie Chisman, Special Projects Director at VELFAC.