Could felt be put in retrospectively on a roof ?

[Angeldelight81]

Basically my brother’s just been up in the loft and the beams are absolutely soaked. I knew there was a problem but obviously I didn’t know what. And he pointed out that there is no felt. It’s literally slight that you can see tacked onto wooden beams so I’m pretty sure I read or heard that the fault could be put on retrospectively. I’m on making that up in my mind or is anybody else heard of it?

Okay, I absolutely will. Thank you that’s a good tip

Seeing chinks of daylight through the roof slates is no issue. How it performs in the rain is the important bit. It’s done ok for 100 years with no felt.
It is possible a couple of slates were broken by the roofers when they did the flashing, but then that would be a localized problem.
You should not insulate between the roof rafters ( under the slates) but you should have deep insulation between the ceiling joists, not just ‘some’.
Too little insulation, and not enough ventilation, would contribute to a lot of condensation. Next time it rains or there is a cold snap, get up there and have a look with a decent flashlight.
One thing to mention, your neighbors have already had their slates replaced, which may indicate yours are coming to the end of their life.

The original roof timbers will probably sag if you put concrete tiles on them.

If you can afford it, have any reroof done in slates. You can get synthetic cement slates that are less expenseive. Re-use the best of the originals on the side facing the road.

Beware any roofer who offers to dispose of your old slates and stacks them carefully in his van. He is going to sell them.

If you go into the loft during daylight hours, are there are obvious holes - i.e. can you see any patches of daylight?

I think you probably need to check the joists after a week without any rain. If they're dry, then it isn't going to be condensation.

Our roof is tiled, but lacks felt. When there is heavy rain and wind ('driving rain') done resin can get under the tiles, but it's very minor and there's zero rot/mould in the roof's structural wood.

The lack of felt means the it's very drafty up there and everything dries easily.

There’s definitely day light coming through gaps

If you need new tiles, have slate again. It'd look terrible to replace slate with concrete. But you did ask about how concrete performs. I have concrete tiles which have been on now for 60yrs and are perfectly fine. I think because they're so heavy they don't wear as much. If I ever had to re-roof though I'd go back to the original terracotta tiles. My roof joists are all supported by steel so the weight doesn't matter.

@Angeldelight81 I think it was £3300 but that was years ago.

@Splonker and @SpottyStripyDuvet thanks