Hello, got a bit of a head scratcher. Currently doing an extension which will have a flat roof which is to join to another flat roof extension. The existing roof was only done a year ago. I know how to lay felt, but how do i go about merging the to felt roofs together, how would i join the felt roofs. the existing is normal style, facia with felt over hanging. Do i bend the existing felt up and over lap it onto the new structure and then over lap my new roof felt onto that, or is it simple and i'm making hard work for myself. I know how to build the roof and join it, it is just the joining of the felts thats got me stumped. Any comments will be greatfuly received.