What makes a window great and what do I need at my location?

An example of a Passivhaus interior showcasing energy efficiency and sustainable design principles in action.

There are thousands of window brands out there, and every brand has various levels of quality. Like “blue Bosch power tools” and “green Bosch power tools”.

Window generals:

  • Bigger is better! If you want a view, choose a few big windows, NOT plenty of small windows. Have square windows, not long narrow ones. The frame to glazing ratio worsens rapidly with small and narrow windows. OK, there is also such a thing as too big! A 5mx5m window is not economical and a nightmare to install.
  • Don’t have dividers in your window, one external frame with one glazing is most cost-effective and performs best!
  • Do NOT use the window-related U-Value, g-Value, or SHGC. You need to get the specific ones of the frame and glazing!!!
  • Are you close to the coast? Consider using marine-grade. (The parts made from metal)
  • Your performance requirements come from your modelling with designPH and PHPP or equivalent.
  • Unfortunately, the regulations provided by the governments are not sufficient. As they do not stick to science and use political factors and lobby factors in their calculations. Real economic decisions can only be made if we stick to science!
floor to ceiling window


  • U-Value Frame – lower is better, the right one for your project comes from the PHPP calculation
  • Narrow frames are better as no solar radiation comes through your frame. We do not want frame we want glazing!
  • Do you have high UV radiation? Do you need UV-resistant coatings? Do not use Red or Black as these colours fade with time. Just look at old cars with those colours, and you know what I mean. 😉


  • U-Value Glazing – lower is better, the right one for your project comes from the PHPP calculation. In Australia and the US, double glazing is often sufficient. Triple glazing is often more economical due to little additional costs – usually less than $5 a square metre.
  • g-Value (often named SHGC, not exactly the same but describes the same) – the right one for your project comes from the PHPP calculation.
double glaze window sample cross section


  • The change over from glazing to frame always causes a thermal bridge, mainly dependent on the spacer. The spacer is the part that keeps the panes of glass separated.
  • Sometimes stainless-steel spacers are OK but not economical. It always makes sense to use high-performing spacers.
  • Thermal bridge value for the spacer (also called glazing edge) should stay below 0.04 Watts per metre Kelvin
  • Aluminium spacers are a no-go. (Don’t believe the manufacturer that says he/she only gets the rigidity of the window by using aluminium spacers

We hope that has clarified what is required by Passive House windows. Remember, windows are a complex technology. If you want to learn more about windows, we highly recommend joining one of our certification courses.

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