Radiation and protection in glass façades – control of light and heat

Glass façades allow natural daylight to enter a building, but they also act as a pathway for solar radiation, heat, and UV rays. Controlling radiation through glass façades has become a key component of energy efficiency and interior protection. Depending on the building’s location, orientation, climatic conditions, and intended use, different types of glass are selected to control radiation and protect the interior from overheating, UV damage, and energy loss.

Controlling radiation in glass façades is essential for energy efficiency, interior durability, and occupant comfort. By selecting glazing with low-emissivity, reflective, and UV-protective layers, an optimal balance between daylight, heat control, and protection is achieved. Technical properties must be certified and compliant with standards, and systems must be properly installed to ensure the declared level of protection.

Types of radiation affecting façades

Solar radiation consists of three components that are relevant for glass façades:

  • Ultraviolet (UV) radiation: responsible for fading of furniture, material degradation, and partially for heat transfer
  • Visible light (VIS): provides illumination of interior spaces but also contributes to visual glare and overheating
  • Infrared (IR) radiation: the main source of heat that causes warming of interior surfaces

Radiation-protective glazing

Modern façade glazing incorporates special coatings or structures that filter specific components of solar radiation. The goal is to allow daylight to enter while blocking UV and IR rays that negatively affect the building’s energy balance.

  • Low-E glass (low-emissivity): reflects thermal radiation back into the interior in winter and reduces external heat gain in summer
  • Solar-control glass: features reflective coatings that reject a portion of solar radiation, especially IR waves
  • UV-filter glass: specially treated glass that filters up to 99% of UV radiation
  • Reflective glass: coated with a metallic layer that reflects part of visible and infrared light

Coefficients describing radiation protection

When selecting façade glazing, specific parameters are used to quantify solar protection:

  • g-value (solar factor): indicates the total solar energy transmission through glass. Lower values mean less heat transfer.
  • U-value: thermal transmittance coefficient; lower values indicate better insulation.
  • TL (Light Transmittance): percentage of visible light passing through the glass.
  • UV transmittance: the amount of UV radiation that passes through the glass.

Protection of occupants and interior materials

Radiation affects not only the building’s energy balance but also interior materials, occupant health, and indoor comfort. UV radiation can cause fading of furniture, floors, textiles, and artworks. Infrared radiation leads to localized overheating, increasing the load on cooling systems.

  • UV-protective glass prevents interior material damage
  • Solar-control glass reduces the need for air conditioning
  • Low-E glass improves overall thermal comfort

Combination of protective layers and multi-pane glazing

In practice, combined insulated glass units (IGUs) are used, incorporating multiple protective features. For example, double glazing with one Low-E layer and one solar-control layer provides effective protection under varying climatic conditions.

  • Applied in commercial buildings, residential buildings, schools, and hospitals
  • Can be combined with acoustic insulation and safety layers
  • Compatible with all façade system types (structural, spider, ventilated)

Standards and technical documentation

Glazing that provides radiation protection must be tested and declared according to applicable European standards:

  • EN 410 – optical and solar properties of glass
  • EN 673 – thermal transmittance of glazing units
  • EN 1279 – performance of insulating glass units
  • EN 1096 – coated glass for low-emissivity and solar control

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