Solar shading is the smart, dynamic insulation of the transparent parts of a building, effectively managing the entry of solar heat and light to provide a thermally & visually comfortable indoor space, that remains cool in the summer and warm in the winter, free from glare all year round, with the view out maintained and minimum energy demand on installed cooling, heating and lighting units. Lean more in this informative guide put together by industry experts.



The Sun is constantly flooding the earth with huge amounts of energy. This energy comprises of 4 main bands; UV (ultraviolet), visible light, near infra-red (shortwave) and infra-red (longwave) radiation. Of the energy that reaches the earth, it is primarily made up of visible light and near infra-red (shortwave) radiation with only 2-3% UV radiation.

When the suns near infra-red (shortwave) radiation strikes glass (or any object), 3 key things happen:

  1. Some of the sun’s energy is directly transmitted through
  2. Some of the sun’s energy is reflected
  3. Some of the sun’s energy is absorbed


The level of transmission, reflection and absorption will depend on the type of glass.

The energy that is transmitted through the glazing, when it hits an object inside the room such as a chair, desk, wall etc along with internal shading devices is absorbed and re-radiated as longwave infra-red ‘heat’ rays.  The same applies to the sun’s energy which is absorbed by the glass, it is converted to infra-red ‘heat’ rays, some of which is re-radiated into the building and some into atmosphere.

The total solar ‘heat’ radiation entering the building is a combination of what is directly transmitted through the glass (ie is going to be converted to heat) and the element of radiation that is absorbed by the glass and re-radiated inwards.

Glazing is virtually transparent to incoming shortwave radiation but when this radiation is converted to longwave ‘heat’ rays, glazing becomes opaque to it, causing the heat radiation to remain trapped in the building and indoor temperatures to rise. The above process is often referred to as the greenhouse effect.


Unlike glazing, which is virtually transparent to the suns radiation, external shading systems are not. When an external shading system is employed outside of the glazing, it blocks virtually all – upto 97% – of the suns incoming shortwave radiation as the majority of the suns energy is either reflected, in the case of lighter colour fabrics or absorbed by the material (darker colours). The radiation that is absorbed by darker colour materials and re-radiated as longer infra-red ‘heat’ rays towards the glazing does not transmit through the glass due to the longer wavelength and this heat between the glass & fabric is simply dissipated as hot air rises.

By stopping shortwave radiation even reaching the glazing, excessive solar heat gain is prevented, with the resultant effect of a naturally air-conditioned internal environment, with minimum load on any installed air conditioning units and a lower energy bill, along with a reduction in a buildings carbon emissions.


Significantly improving the performance of glazing, the charts below detail the typical solar and optical performance of common glazing types unshaded and shaded with either an internally or externally mounted blind system. When any glazing type is shaded with an external blind system, there are significant improvements in the performance of the glazing, keeping a room/area cooler and free from glare.

Heat Transmission – Keep Cool in the Summer

Glazing Type No Shading With Interior Blinds With External Blinds
Single Glazing 85% 54% 11%
Double Low-E Glazing 70% 53% 7%
Triple Glazing 60% 52% 4%


The lower the heat transmission, the less heat that is transmitted into a room and the cooler it will remain. When modern double low-e glazing common in new build and refurbished properties are equipped with external blinds on average 93% of incoming solar heat is blocked (less than 10% heat transmission), a cut of more than 900% in comparison to no shading and external blinds perform 4 x better than their interior blinds counterparts.

Light Transmission – Free from Glare all year round

Glazing Type No Shading With Interior Blinds With External Blinds
Single Glazing 89% 18% 17%
Double Low-E Glazing 75% 16% 14%
Triple Glazing 70% 15% 14%


A light transmission figure between 10-20% ensures on bright Summer days excessive light is cut to prevent glare whilst good light levels are maintained to avoid the need to use artificial lighting.

UV Filter – Optimum Protection

A minimum 95% UV block up to 99.9% is provided, ensuring fixtures and furnishings are protected from bleaching by the sun and skin remains safe.


Windows are responsible for a large portion of the heat lost from a building, in fact, even the best quality glazing loses heat more quickly than an uninsulated cavity wall. Air trapped between the glass and fabric on sealed (tracked) external roller blind systems systems creates an additional layer of insulation to the glazing, helping to slow heat loss, keeping a room / building warmer without the need to switch on heating units.

External blinds (as can be seen by the chart below) help stop heat escaping (lowering the U-Value – thermal heat transmittance) through glazing when installed in combination with older glazing types; bot­h single glazing and first generation double glazing, still featured in much of the UK’s existing building stock. Heat loss can be cut through a single glazed window by almost 50% and a first / early generation double glazed window by virtually a 1/3rd, improving the performance to that of a modern day, efficient low-e double glazed window unit.

Heat Loss – Stay Warmer in the Winter

Glazing Type No Shading With External Blinds
Single Glazing 5.7 u-value 3.5 u-value
Double Glazing 3.0 u-value 2.0 u-value
Double Low-E Glazing 1.6 u-value 1.3 u-value
Triple Glazing 0.6 u-value 0.6 u-value


The lower the u-value, the slower the heat loss through the glazing and subsequently the warmer a room/area will stay.


To ensure optimum comfort levels and to deliver maximum energy saving function, external blinds should be able to react automatically to the ambient conditions.

External blinds do not lower temperatures in the summer, they stop them rising in your home and for this reason, to ensure optimum comfort levels and to deliver maximum energy saving function, external blinds should be linked into intelligent sensors that constantly monitor the ever changing weather conditions, automatically positioning the blinds to allow buildings to passively cool and heat, reducing solar gain in the summer and maximising it in the winter without the need for energy hungry cooling and heating devices.

Many factors affect the correct positioning of external blinds, along with the position of the sun in the sky, the level of cloud cover, shelter from surrounding buildings & objects such as trees, orientation of the façade and amount of glazing all have an impact on the amount of solar gain & light striking the building and subsequently ideal positioning of external blinds.


The most commonly seen and popular type of external shading system is the retractable folding arm patio awning. Mounted on the façade normally above patio doors of all types (sliding, folding, traditional) they project out creating an overhang that regulates solar heat and light to the adjoining internal room, whilst also providing a roof to the terrace that offers shade and shelter for alfresco living – outdoor living & solar control in one solution.

Tensioned external roof blinds also referred to as conservatory awnings run over along with conservatory roofs, all types of flat and inclined skylights and rooflights, whilst external roller blinds & screens run down in front of all types of vertical glazing including sliding and folding doors.

Louvered roof pergolas are a relatively new type of shading system to the UK. When installed abutting a property, the rotating roof louvers (like a Venetian blind but mounted horizontally) can follow the direction and angle of the sun to provide precise sun control along with ventilation through.


Note. Performance data is purely indicative based on independent calculations carried out by Sattler AG and Sonnergy Ltd assuming for both internal and external our Antiguan sealed blind system in the lower position with a 40mm air gap (clearance) between the material and glazing.