I have a flat roof which currently covers the kitchen and bathroom, the total space would be around 20'x8'. I am hoping to turn the space into a garden area with all the planting being done in containers and raised beds.
Currently It has a bitumen felt covering which is looking a little tired, and has a couple of dips and sags. My first thought had been to redo the covering with a bitumen roof paint, however that will still end up with patch of water sitting. Now I am considering making a slightly raised deck and having a very shallow angle across the roof width, my thoughts being grooved boards will take water quickly away from the roof and into the guttering.
As all the containers will be made from timber and most will be quite large I can forsee there being in the region of 6m cubed of soil in total. I'm wondering what sort of weight can this form of flat roof happily support before major structural changes need to be done?
So is the weight allowance for my roof likely to be far below my intended use? and will a sloped deck allow me better good water removal or is it in need of expensive repair?