Roof Strengthener Lower Repair 68-79. 211-817-557L 211817557L £12.00 inc. VAT (where applicable) Quantity: at £12.00 each Add To Basket This is the lower roof strengthener repair. The roof section of a baywindow is made up of 3 parts. The roof gutter, then below that is the strengthener, this is the piece that the strengthener then fits on. Fits all baywindow 68-79.