Choosing the right glazing is an important part of designing a high-performance façade. Glass influences not only the appearance of a building, but also its thermal performance, indoor comfort, energy consumption and the dimensions and weight of the façade elements.
Two commonly used types of high-performance insulating glass are HR++ and HR+++ glazing. But what exactly is the difference between them, and which option is most suitable for your project?
What is HR++ glazing?
HR++ glazing is high-performance double glazing consisting of two panes of glass separated by a cavity. This cavity is filled with an insulating noble gas, such as argon.
In addition, one of the glass surfaces is provided with a low-emissivity coating. This coating reduces heat transfer through the glass and helps retain heat inside the building.
HR++ glazing generally achieves a Ug value of approximately 1.0 to 1.2 W/m²K.
The lower the Ug value, the better the thermal insulation provided by the glazing.
What is HR+++ glazing?
HR+++ glazing, also referred to as triple glazing, consists of three panes of glass separated by two insulating cavities.
As with HR++ glazing, these cavities are generally filled with an insulating gas and the glass incorporates low-emissivity coatings to reduce heat transfer.
The additional pane and second insulating cavity result in significantly better thermal performance.
HR+++ glazing generally achieves a Ug value of approximately 0.5 to 0.8 W/m²K.
This makes triple glazing particularly suitable for projects with ambitious energy-performance requirements.
What is the difference between HR++ and HR+++ glazing?
The main difference lies in the construction of the insulating glass.
HR++ consists of two panes and one cavity, whereas HR+++ consists of three panes and two cavities.
As a result, HR+++ provides better thermal insulation. However, it is also thicker and heavier than HR++ glazing.
This difference in weight and thickness can influence the design of the aluminium frame, particularly for large glazed areas and moving façade elements such as doors and sliding doors.
The choice should therefore not be based on the Ug value alone.
What does the Ug value tell you?
The Ug value indicates the amount of heat that passes through the glazing. It is expressed in W/m²K.
A lower Ug value means less heat is lost through the glass.
For comparison:
HR++ glazing: approximately 1.0–1.2 W/m²K
HR+++ glazing: approximately 0.5–0.8 W/m²K
However, the Ug value only represents the thermal performance of the glass itself.
When assessing the performance of the complete window, the Uw value is more relevant. This value takes into account the glazing, the frame and the thermal performance at the edges of the glass.
Is HR+++ always better than HR++?
From a purely thermal perspective, HR+++ glazing performs better than HR++ glazing.
However, this does not automatically mean that triple glazing is the best solution for every project.
Several factors need to be considered, including:
- the required thermal performance;
- the dimensions of the glass;
- the weight of the glazing;
- the type of aluminium frame;
- whether the element is fixed or moving;
- solar heat gain;
- daylight requirements;
- acoustic performance;
- the building's overall energy concept.
For renovation projects, for example, HR++ glazing may provide an excellent balance between thermal performance, weight and existing construction constraints.
For new-build projects with ambitious energy targets, HR+++ glazing may be the more appropriate choice.
