Glass façades on building developments are a common sight all over the world, particularly in cities. Whilst this is aesthetically popular, it can introduce planning hurdles around glint and glare i.e. the reflection of sunlight by a building causing a safety hazard or a nuisance.
A related, but separate, effect is the potential for a glass building to focus the sun’s rays, creating the potential for heat damage. This has led to high-profile safety issues for buildings such as 20 Fenchurch Street in London which melted parts of a nearby car and the Vdara hotel in Las Vegas which reportedly burned a guest.
Heating issues due to solar convergence are typically caused by concave reflective surfaces that face south (in the northern hemisphere). This article is on the topic of glint and glare in the context of causing a distraction or inconvenience to an observer, which is a more common concern as it can apply to any building development comprising a reflective surface. Most often concerns relate to glass façades, but they can also apply to metallic roofs, wall sections or other reflective surfaces.
Figure 1: One World Trade Centre – New York City
A new problem
The issue of glint and glare as a planning constraint is a relatively new phenomenon in many countries. It is not entirely clear why this is the case. It could be that there are many more buildings with reflective surfaces than there used to be, or that there is generally more focus on safety and residential amenity than was previously the case. Another potential contributor is the progress of the solar photovoltaic industry – where glint and glare effects are a more prevalent concern. This may have brought the issue to the attention of stakeholders and planners who had perhaps not considered it before.
Developments that require glint and glare assessments
Virtually any development that comprises metallic or glass exterior elements can trigger a glint and glare concern. The risks are generally highest for:
- High-rise developments e.g. comprising more than five storeys.
- Developments with a continuous glass façade.
- Developments adjacent to railway lines e.g. within 100 metres.
- Developments close to airports e.g. within 5 km.
The above are not, by any means, hard and fast rules. It is very rare for planning authorities or even individual stakeholders to define quantifiable parameters pertaining to glint and glare concerns. The most common concerns that a developer must contend with are:
- Effects towards road users, which is a safety concern due to potential distraction of a driver.
- Effects towards pilots of aircraft or personnel within air traffic control towers, which is a safety concern due to potential distraction of these observers.
- Effects towards residential properties, causing a nuisance which affects residential amenity.
- Effects towards train drivers and railway signals, which is a safety concern due to potential distraction of a driver or potential illumination of a signal (giving it the appearance of being on when it is not).
Figure 2: A helicopter operating alongside tall buildings with glass façades
What to do
When proposing a new development, particularly one that meets the criteria set out above, it is a good idea to identify and assess receptors that could be affected by glint and glare.
The process for carrying out a glint and glare assessment, in broad terms is as follows:
- Identify potentially affected receptors.
- Define which façade(s) of the development will:
a) Be potentially visible to the receptors.
b) Comprise reflective elements.
- Quantify the dates and times at which reflections are possible towards each receptor throughout the year (technical assessment requiring a bespoke modelling package).
- Evaluate the predicted technical effects in an operational context considering:
b) Position of reflector relative to observer e.g. is the reflection occurring directly in front of a driver or off to one side?).
c) Incremental increase in effects based on the existing environment e.g. is the development being added to an existing cluster of similar ones or is it introducing a reflector in an area that does not have any?
- Devise a mitigation strategy where necessary.
- Consult with the relevant bodies following completion of the above.
Mitigation options depend on the nature of the predicted impact and the receptor type. Options can include:
- Provision of screening e.g. shielding a receptor from potentially reflected sunlight.
- Utilisation of less reflecting materials.
- Design changes.
A mitigation strategy should be devised taking into consideration the level of impact and the nature of the receptor. This can require coordination with the potentially affected stakeholder.
Pager Power has conducted over 400 glint and glare assessments throughout the world including Europe, Africa, India and Australasia. The company has developed good relationships with aviation and railway stakeholders in many countries and assisted in overcoming glint and glare issues for numerous projects (see our projects page for more information). If you wish to discuss any of your existing or upcoming projects, please do not hesitate to contact the team.