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Short question: Can GRP or EDPM products be successfully applied onto the top of existing felt substrate?
Background: We have a relatively large 'L' shapped flat roof (48 square metres in total) as part of our house (converted garage one side, single story extension on the other).
Existing covering is felt that is approx 10 years old and has had minor patching (leaks) done at some point in the past and the roof does suffer from ponding.
Looking at products like polyroof185 I had understood that the old substrate would need to be completely removed with a new board base put in place.
I have, however been recommended to not go to the expense of replacing the whole roof (the substrate is 'sound') and instead have an EDPM layer applied over the top of the existing felt, with a number of mushrooms vents installed through the existing flet/boards in order to allow any existing trapped moisture to escape.
Can this overlay option really give a comparable life extension to the flat roof or should I push for the whole roof to be replaced? Obviously there is going to be a significant cost difference.
Thanks
Background: We have a relatively large 'L' shapped flat roof (48 square metres in total) as part of our house (converted garage one side, single story extension on the other).
Existing covering is felt that is approx 10 years old and has had minor patching (leaks) done at some point in the past and the roof does suffer from ponding.
Looking at products like polyroof185 I had understood that the old substrate would need to be completely removed with a new board base put in place.
I have, however been recommended to not go to the expense of replacing the whole roof (the substrate is 'sound') and instead have an EDPM layer applied over the top of the existing felt, with a number of mushrooms vents installed through the existing flet/boards in order to allow any existing trapped moisture to escape.
Can this overlay option really give a comparable life extension to the flat roof or should I push for the whole roof to be replaced? Obviously there is going to be a significant cost difference.
Thanks