How to find your window's external frame dimensions:
Deduct approx. 2 cm* from the brick opening = Window's/door's external frame dimensions
Example:
Brick opening 103x103 cm = Window's external frame dimensions 101x101 cm
*It’s important that there is space for insulation and a seal around the edge between the window and the brickwork. We advise to deduct approximately 2-2.5 cm from the brick opening to ensure that the insulation won’t be too compact and that the window has space too "breath" (approx. 1 cm on each side and top and bottom).