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Efficient windows in a passive house

Key parameters of efficient windows in a passive house

Windows are the sensitive point of housing and are responsible for 22% of heat losses in a passive house (12% from frame and 10% from glazing).

It is essential to choose windows correctly in order to minimize these heat losses.

But windows also bring light into the house, provide ventilation, regulate solar gains inside the building and provide a view of the outside.

The glazing must both minimize heat losses and allow enough solar radiation to pass through to heat the house. It is therefore necessary to find a balance between thermal losses and solar gains. The glazing must therefore meet certain thermal characteristics.


The different types of glazing

  • Single glazing Ug = 5.5 W/m²K
  • Double glazing with air gap Ug = 3 W/m²K
    • Or noble gas Ug = 2.2 W/m²K
    • Or noble gas and low-emissivity coating Ug = 1.3 to 0.9 W/m2K
  • Triple glazing with air gap Ug = 2.3 W/m²K
    • Or noble gas and low-emissivity coating Ug = 0.8 to 0.5 W/m²K


The window frame is the weak point because it blocks the sun’s rays (we should limit its proportion to 30% of the total window).


The passive standard does not require any materials, so it is possible to opt for solid wood, PVC or Aluminium frames. In the latter case, the frame must be made of a thermal bridge breaking system.

Recommendations for a passive building in Central Europe (mild and temperate climate):

  • U between 0.85 and 0.70 W/m2K
  • Triple glazing
  • Insulated frames
  • Highest possible solar factor (g = 50%). This makes it possible to keep the heat indoors during the winter and allows lower indoor temperatures in the summer.

Recommendations for a passive house in Portugal :

  • U can be up to 1,70 W/m²K
  • Double glazing
  • Insulated frames
  • Solar factor G = 60%

The installation of windows is also to be taken into consideration to minimize heat losses, therefore they must be aligned in the thickness of the exterior insulation. It will also be necessary to consider airtightness when installing windows.

Check out this page to find a list of companies that are manufacturing efficient windows for your passive house in Portugal.