Windows and doors
Windows and doors play a major role for the energy loss of a building. Therefore, it is important to select the windows and doors for low energy buildings with great care:
- The glass in low energy windoms must consist of preferably three layers of energy glass.
- The glass must consist of two or preferably three layers of energy glass
- The frames must be designed to limit the loss of energy in the joints between the glass and the frame
- The joints between the frame and the walls must be sealed with suitable materials
- The bigger the frame area, the higher the energy loss. This means that a few big windows are a better solution than many small ones and bars should be used with great care
- Windows for extremely low energy buildings should have a total U-value no higher than 0.70 – 0.85 W/m2*K
- Doors that are not of glass should include insulation in their core and thermal bridges should be avoided to the extent it is possible
Another factor to be aware of is the g-value of a window which determines how much of the heat from the sun is allowed to enter the building. The higher the g-value, the more passive solar heat gain in the building. Today, the g-value in low energy windows should always be higher than 0.5. A high g-value improves the energy efficiency of a building, but also increases the risk of overheating and the need for sun protection.
