Window glazing and frames
The entire window, ie: glazing and frame, should have a U-value of 0.80W/(m²K) or less (this
value may have to be more stringent in more extreme climates, whereas milder climates may
manage to meet the criteria with higher U-values) and the installed window should have a total Uvalue of no more than 0.85 W/(m²K). It is therefore essential to use well-insulated window frames
with multiple lip packing. Glazings should have a high total solar transmittance (g-value) of at
least 50% making a net heat gain possible during the winter (although lower g-values may be
appropriate for extremely warm, sunny climates). The windows themselves must be airtight and
the spacers in the glass seal edge must be thermically separated, ie: not aluminium. Windows
should be installed in a thermal bridge free manner in the insulation layer.
Window orientation and shading
Appropriate window orientation and shading are essential for Passive Houses. To capture as much
of the sun’s energy as possible when it is needed most, the largest window surfaces should face
the equator it at all possible. When designing the windows, it is important to reduce the amount
of window framing to a minimum so as to minimise unwanted heat losses (or gains). To prevent
overheating, windows facing East and West should be equipped with shades. Especially in warmer
climates, shades are also recommended for windows facing the equator. In order to ensure
adequate cross ventilation on warmer days, every outward facing room must have windows that
can be opened.