Repair foil under roof tiles

Good evening,

I have a question, I want to gradually complete some tasks. This includes the new insulation of the roof surface in the extension. Normally, the structure of a roof surface is as follows (from outside to inside):

[*]Roof tiles
[*]Battens for tiles
[*]Foil
[*]Rafters with insulation
[*]Foil
[*]Battens for drywall or similar
[*]Gypsum board or similar

The foil under the battens is not continuous over the entire area; there were 2 transparent roof tiles made of plastic installed in the roof surface, and the foil was interrupted there. Now the question arises, can I simply renew a part of the foil from the outside and seal it with the appropriate adhesive tape at least for the time being? Because I do not currently have the possibility to remove the roof tiles and battens, then reapply the foil and cover the roof again. Therefore, the idea was to repair it appropriately from the outside so that the insulation and so forth can be done normally from the inside.

So the question is, is something like that possible? Or is there anything to consider? Apart from falling off the roof.

Michael

If you can properly bond the "patch" to the existing underlay membrane on all sides, there is actually nothing against it.

Okay, better to apply the "patch" from the outside or inside?

As a layman, I would do it from the outside, first clean the foil properly so that the adhesive tape can stick properly. And then glue the patch from outside and inside on all 4 sides. The foil should then be tight enough that I can "test" whether it is sealed, with a watering can and then check from inside if it stays dry, right?

Because at least I know from other work that I check the work to see if the operation was successful, especially when it becomes harder to access afterwards or the damage could get worse.

Michael