I have had this question for a number of years but after the last few weeks of constant rain its popped into my head again.
Has anyone retrofitted Sarking to the underside of their roofs? Is it possible? and is it worth an attempt?
I have no sarking
There is left over insulation from someone before.
The tiles seem to be watertight except for the stay wires coming through the tile and beams.
Water seems to get blown up under the tiles or backed up from leaf matter outside to gain entry into roof cavity.

This was from 2021, pretty much the same as this weekend. Ihave a bucket with a towl across it to stop the splash and so far no actuall puddle ammount has come through but the towl is soaked.

I was thinking of attaching sarking with a bit of a dip between the trusses, mainly to stop these drips. My concern is will anywind/breeze will want to flutter it around?

I may try to retrofit above the bathroom and kitchen areas first and see if iuts stands up to the wind.

From 2022 and still the same (The light well is corflute of skylight installed before my time. Dodgy bro inc id say.)

From 2022 and still the same. The plaster has a silver reflective to the top of it for the whole house. I do not know if its conductive lol Yeah I turn the power off to the house when I go up there just in case.

From 2022 and still the same tho that hole has been fixed towards the left.
The plaster in the ceiling of the bathroom has paint issues from the condensation of water as the room is in the middle of the house. The "join" is where the watar drips through. Both of these are on the list to be fixed but first would be stopping leaks.
Dave