The installation of a window into a wall must:
- Protect the structural integrity of the window in that, the window should not support any load other than its own weight.
- There must be an air tight seal around the window.
- There must be continuous and unbroken thermal insulation between the frame of the window and the wall.
- There must be some allowance for differential movement between the window and the wall opening.
- And finally, that installation must serve to maximize the performance of the energy-efficient features of the window.