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Isothermal protective glazing in front of historic church windows

Updated: Apr 1, 2023

Isothermal protective glazing is installed before stained glass for the best possible preservation. As a rule, these were and are used for stained glass windows in churches.

Our decades of experience show that in most cases the construction principle of a front glazing functions. Similarly, due to the simplicity of the materials (wood, metal, mastic, glass) and the construction, this system is less invasive and correspondingly sustainable.

Moisture forms on the inside of the glass windows due to temperature fluctuations and the resulting shift in the dew point. To counteract this, a frameless, simple front-mounted exterior protective glazing is an effective solution.


The rear ventilation of the church window causes a chimney effect, an even ventilation of the space between the windows. This prevents condensation and standing humidity from causing further damage.

Such glazing is mostly installed in combination as isothermal and exterior protective glazing to protect against mechanical damage.

Depending on the profile of the reveal, attention must be paid to the local climatic conditions. In particular, the conservation effectiveness.

isotherm 2

In the case of objects that are particularly worthy of protection, the stained-glass is curtained off to the inside. The protective glazing then functions in the original window rebate. The space between the stained-glass that has been moved inwards and the protective glazing must be ventilated from the inside. The stained-glass would thus be surrounded on both sides by the interior climate of the church and thus "isothermal".

The exterior view of the monuments is also decisive for the design principle.

If historically valuable objects are under the strong influence of daylight, they are exposed to ultraviolet radiation. The UV rays have been shown to bleach colour pigments. As a result, irreversible material changes occur. This radiation can be prevented with mouth-blown special glass. The filter effect is achieved with innovative glass components. In this way, a simple pane with a material thickness of 2 to 3 mm can easily be installed in narrow glass rebates of historical windows.

We obtain these special glasses from the Lamberts glass works. With its typical surface movement, this glass blends in with the historic building fabric.

We are committed to the preventive conservation of valuable art and cultural assets.

The Domglas Naumburg Team

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