Answer: It is possible to repair a flat roof yourself, but you would need to make sure that any fix you make will need to be completly 'water tight'. Removing any dust, grease or dampness from the area in which you are going to fix a patch. If your problem was caused by something puncturing the felt, then it is worth repairing, however, if it 'just started leaking' then it might be false economy to repair, and cheaper in the long run to replace the felt with HT Felt. To repair a flat roof properly, you need good felt and boiling bitchimum to ensure a proper water-tight seal. The latest technology is EPDM and has a Longevity (guaranteed for 20 years but known to last a lifetime).