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Roof windows: insulated glass to prevent the room from heating up

Sun protection is especially important for skylights. In addition to various shading solutions (e.g. roll-up or roller blinds), roof windows can be equipped with insulated glass. In this article, you can find out how it works and what options are available.

Roof insulation windows

Sun protection glass function

Sunscreen glass has the function of preventing excessive indoor temperatures in summer. Therefore, the incident light beam must be absorbed or reflected by the glass itself. In both cases, the exterior of the glass has a very thin coating or some additive. However, the function of this coating is different for absorbing glass and reflecting glass.

Absorption glasses

Some of the glass that absorbs the heat of the sun’s rays contains certain metallic impurities, usually, these are.

Divalent iron oxide

Trivalent iron oxide or

copper oxide

These substances in the glass absorb the energy of the sun’s rays and then release it to the outside. The efficiency of these windows may vary depending on the type and number of mixtures.

Reflective glasses

Reflective sunscreen glass has a special reflective coating. The coating can reflect both in the infrared range (thermal radiation only) and in the visible range (additional glare protection).

Normally, thin films made of metallic semiconductors are used for the coating. The thickness of the coating is so thin that it is almost imperceptible to the naked eye.

Switchable glasses

In recent years, an increasing number of switchable glasses have entered the market. The manufacturing difficulty and production costs of this type of glass have been significantly reduced. Nevertheless, the price is still significantly higher than that of conventional glasses.

Sun protection glass function


Switchable glass consists of two pieces of glass laminated together with a film of thermochromic or electrochromic glass between them.

Thermochromic glass can be switched automatically depending on the glass temperature, while electrochromic glass requires a low current for coloring and decolorization.

Since a voltage between 1 and 3 volts is usually sufficient, the voltage generated by the battery is also sufficient. Electricity is only needed during tinting or decolorization. After that, the system can remain current-free.

Newer glasses already have a gradual switching function. In up to five stages, the thermal radiation can be reduced by 30 to 90 percent.


The efficiency of sun protection glasses depends on the type of glass. In addition, Parlun offers sunscreen glasses with different efficiencies to meet different requirements and installation locations.

The G-value (total energy transmission) is decisive for effectiveness. This is the value that quantifies the amount of solar energy that can still enter the room. the lower the g-value, the more effective the sun protection. For modern glass, these values range between 0.18 and 0.48, while values for insulated glass are slightly higher, at around 0.6.

However, special solar and thermal barrier films offer roughly the same protection at a much lower cost.

The disadvantage of insulated glass for roof windows is that they cannot use the sun’s rays to support the heating system in winter. This is a major advantage of switchable glasses.

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