BW-02Work out what's behind the wall at each bracket pointBay windows often mix construction — the corner piers may be solid brick or block, while the flat sections either side can be timber stud, metal stud, dot-and-dab plasterboard, or old lath and plaster. Check each bracket mark separately with a stud detector or magnet: a line of screw heads under plasterboard means a stud behind, a hollow sound between them means just board. Drill a small 2mm pilot hole at each mark — pale dust means timber, fine grey swarf means metal, and a dead solid feel with brick-red dust means masonry. Don't assume one wall type applies right round the bay.