VB-02Work out what's behind the wall above the windowRun a detector across each marked bracket position to check for timber studs, metal studs, or solid masonry, and to pick up any cables or pipes. A line of screw heads under the plaster, a solid knock, and timber dust from a small test hole all point to a timber stud. A hollow, drum-like sound between evenly spaced upright lines, and fine grey swarf instead of dust, means metal studs — common in flats and anything built or refitted since the 1990s. If the wall sounds solid all over with no give, you're likely into brick or block, or plasterboard fixed to masonry with dabs of adhesive (dot-and-dab) rather than a timber frame.