For window openings, fix the boards to the wall as normal, making sure the cut edges are at the sides of the window. Full boards that have not been cut can then be fixed to the wall under the window opening. At the top of the window, adhesive should be used so that curtain rails can be fixed. Strips of board should be cut to the correct size for the reveals. The strips of board should then be nudged back so that it is in line with the edge of the face board and the window frame. The cut edge of the board should be on the window side of the reveal.
The plasterboard that is being used on the top of the window should be wedged in place with either lengths of wood or plasterboard.