Length of the sills
Measure the length between the window opening and add +2 cm to this length on each side. For example, if you measure 100 cm between the walls on each side, then the length of the stone shelf is 104 cm.
If the window opening walls have not yet been finished and you start from the length of the window itself, then take the length of the window and add +1.5 cm to it on each side. For example, if the window is 90 cm long, then the length of the stone shelf should be 93 cm.
Width of the window sills
We recommend that the outer window shelves have an overhang of 4.5 cm, and the inner shelves 3 cm.
Use a tape measure to measure the distance from the window to the edge of the wall over which this window sill will look. Add 4.5 cm to this distance for outer or 3 cm for inner shelves.
For example, if you measure 20 cm from the window to the edge of the Styrofoam or the wall, then add another 4.5 cm to this distance for the outer shelves.
Window sill thickness
Regarding the thickness, we recommend choosing a thickness of 3 cm for the outer shelves or 2 cm for the inner shelves. However, both thicknesses are used for the outer and inner shelves, so both are possible. The main advantage of 3 cm thickness is that it looks more massive.
left& right side grooves on the top surface
For external window sills, we also recommend side drainage on the upper surface of the shelves. There are drains on the left and right sides, and they prevent water from draining onto the facade on the sides. For the outer shelves, the drip edge is at the bottom, already included.