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Night view of a high-rise building with an open parallel window in the glass façade.
07 Mar 2022

U-value: what does thermal insulation mean for your building project?

Sustainable homes and buildings are the only way forward. Every aspect counts. A less known, yet extremely significant factor to measure energy efficiency is the U-value. The lower it is, the better the thermal efficiency or insulation.

Rising energy costs and growing sustainability awareness have considerably increased the focus on a building’s energy performance. Efficiency standards – imposed and often made stricter by regulation – are a major indirect driving force behind enhancing the comfort level of a project. Thanks to an optimal U-value, you not only save energy, you also increase your quality of life.

A good U-value contributes to energy savings, as well as quality of life.

U-value, formerly known as K-value, is used in the construction industry to indicate to what extent a material is thermally insulated. The lower the U-value – or, “thermal transmittance” – the higher the heat resistance of a material – thus, the better the insulation. Because the thermal transmittance is determined by the profiles of windows and doors, plus the glass, the U-value of both components should be considered for the joinery of an aluminium construction.

Detail view of the Reynaers Experience Centre’s glass façade.

Saving energy with aluminium and glazing

The building industry distinguishes five categories:

  • Ug-value: the U-value of the glazing. G stands for glass.
  • Uf-value: the U-value of the chosen profile. F stands for frame.
  • Uw-value: the U-value of your entire window. W stands for window.
  • Up-value: the U-value of the aluminium panel in your door. P stands for panel.
  • Ud-value: the U-value of your entire door. D stands for door.

And then there is the Psi-value, which affects the total U-value and expresses the heat loss at the transition from the glass to the window frame, measured over a given length. Choosing the best insulation solution means not only taking into account the insulation value of the profiles but also of the glazing of your moveable or fixed vent. The full package is what helps you save energy.

Sustainable living and working

Reynaers Aluminium not only cares about energy efficiency. Your comfort counts too. An excellent duo, as the latter is often generated by technological innovations that focus on efficient energy use.

In thermal insulation, some of our Reynaers Aluminium systems have reached a limit for U-values at Passive House level, well under 1.0 W/m²k. Ventilation, solar control and airtight building connections are essential as well. The mix of all these elements makes it possible to achieve a comfortable climate, even directly behind a large glass façade, regardless of the weather. That is what we call “quality of life”.

Woman indoors, standing in front of large sliding window.


Reynaers Campus: Experience Centre – Jaspers-Eyers Architects (architect); Phillippe Van Gelooven, Georges De Kinder (photographers)