Sealing a flue hole within flat roof.

Hi,

I have a existing flat roof with a now redundant 4'' flue hole/18'' square flashing plate. I've temporarily sealed the hole/plate but I now need a more permanent solution.

The existing felt system appears to be in a reasonable condition (it's around 8 years old) and has been painted with a reflective coating. Ideally I don't want to replace the entire covering for a few years yet so can anyone advise on the best way to repair it?

I've considered cutting the felt and removing the plate, repairing the hole and patching the felt etc but am unsure as to the types of materials and methods I should use.

take off the plate and just fill hole with expanding foam to retain insulation value and not cause a "cold spot"..then after its set get a piece of code 5 lead to cover hole and repair with normal felt work to an area 4-5 time the size of affected area