Double-Pane Windows

The Old Standard of Insulation

Dubbel glas (double-pane windows or double glazing) refers to windows constructed with two panes of glass separated by a sealed air gap. This design became the standard for construction and renovation in the Netherlands from the late 1970s and 1980s onwards, as it offers a significant improvement in thermal and sound insulation compared to old-fashioned enkel glas (single-pane glass). Today, having at least basic dubbel glas is considered the minimum acceptable standard for a decent rental property. However, technology has advanced significantly, and a savvy tenant should learn to distinguish this older standard from modern, high-efficiency glass.

The Critical Difference: 'Dubbel Glas' vs. 'HR++ Glas'

Many landlords or real estate agents will advertise a property as having 'double glazing'. This statement, while technically true, can be misleading. There is a vast difference in performance between the simple dubbel glas of 30 years ago and the modern High-Efficiency (Hoog Rendement - HR++) glass available today.

• Standard Dubbel Glas: The space between the panes is filled with air. It reduces heat loss, but is not highly efficient.
• Modern HR++ Glas: The space is filled with an inert gas (like Argon) and one of the glass surfaces has a special transparent, heat-reflecting coating. This combination is far more effective at preventing heat from escaping in the winter.

The difference in your annual heating bill between a house with basic dubbel glas and one with HR++ glass can easily amount to hundreds of euros. When viewing a property, you can often identify modern HR glass by looking for a small code (e.g., HR++) printed on the metal spacer bar between the two panes of glass. The absence of such a code often indicates it is the older, less efficient type of double glazing.