I have a single story GRP flat roof that is 5m x 5m. The joists are 225mm x 50mm and are spaced at 400mm centres.
I want to put a glass skylight in the centre, it is 1.7m x 1.3m and weighs approx 100kgs.
Could anyone advise on what size joists and trimmers I'll need to put in to support it...