My garage has been converted and a warm, raised EPDM rubber flat roof has been used to replace the old roof. Unfortunately the roof needs redoing as the builders did a shocking job, which they have admitted fault and replacing at their expense. One of things I spotted when they did it the first time is that they did not remove the old felt. From what I saw, they laid insulation boards over the old felt, waterproof T&G chipboard ontop and laid the EPDM on top of that. Should I be asking them to remove the old felt when they do it again or is it not something to worry about?