Last update: 15.10.2020
Solar control

Sun protection in summer

Modern insulated glass allows short-wave solar radiation to pass through without hindrance, but the majority of long-wave heat radiation is reflected back to the interior.

This results in solar heat gain in the cold seasons. ln summer, however, this solar radiation can result in overheating.

In addition to other energy sources (see figure below), the position and size of the glazing are critical. In general, windows or façades with large glazed areas that face East, West and particularly the South, should be equipped with suitable sun protection glazing.

Heat losses and energy gains

Specific requirements need to be met to prevent overheating that can result from large glass surfaces, starting with the solar input factor S.

In general, the following rule applies according to DIN 4108:

S existing   ≤   S admissable  

The admissible solar input factor results from the proportional input factors.

S admiss.   =   S1 + S2 + S3 + S4 + S5 + S6


The proportional input factors depend on:

S1: utilisation of the building (residential/commercial, climate zone, type of construction, night cooling) – see DIN 4108-2, table 8.

S2: percentage of window area.

S3: solar control glass.

S4: glazing slope.

S5: glazing orientation.

S6: passive building cooling


The existing solar input factor results from the following equation:

Solar input factor equation

AW,j:        glazed area in m²

AG:          ground area of the room in m²

gtot,j:       (total) solar factor including mechanical shading:

                                    - EN ISO 52022-1

                                    - EN ISO 52022-2

                                    - based on EN 410

                                    - manufacturer statements


Determination of gtot is carried out using the following equation:

g tot   =   g x Fc


g:         solar factor of the glazing                  

Fc:        reduction ratio for shading devices

The generalised reduction ratio FC for fixed installed shading systems can be taken from DIN 4108-2, table 7.

A detailed method for the determination of gtot is available according to EN ISO 52022-2. This method considers the specific physical properties and the interactions of a defined shading and a defined glazing. The calculations are to be carried out using special software tools.

The Guardian Technical Advisory Centre can support with related calculations on request.

Looking for solar control glass?

Regardless of what the building’s architectural or building physical requirements are, the broad SunGuard® glass range can provide an optimum transparent solution.