Some kind of rot - in need of advice (with pictures)

[Stimpleton]

Hi all, I discovered a gap in my roof lining the other day with a little pile of woody debris under it. On closer inspection the surface of the batten exposed by this gap feels soft and crumbly. But despite a wet few days the whole area seems dry, and the ceiling immediately beneath has never shown any signs of water ingress.

It's in a very tight spot so I can't get my eyes up close but have managed to take some pictures. The first one shows the general scene, the other two are of the batten. If you zoom in there seems (to my uneducated eye) to be some dark fungal growth, reddish looking fruiting bodies and a few white patches.

I am concerned this might be dry rot and clueless as to how worried I should be and what steps to take next. I have no roofing knowledge or contacts so any advice would be very much appreciated.

The house is an early 60s dormer bungalow by the way. The tiles look in decent condition from the outside, and we had a full survey done before buying a couple of years ago but I appreciate surveyors don't go around exposing timbers to check for decay.

 

[vinn]

Someone has previously opened up the felt and probed the tile lath.
The felt seems to be mineral faced flat roof capping felt. It typically needs full support. But, anyway, its not a suitable felt as an underfelt on a concrete tiled roof. Are there any signs of condenation in the loft?
The question is, why has the tile lath wet rotted: I dont see signs of dry rot? Possibly there's a leak further up the roof or an excess of condensation under the tiles?
Someone should go up on the roof and lift some tiles in that area to examine the state of the surrounding tile laths.
The Dormer flashings should be carefully examined by gently lifting and looking underneath them for evidence of damp.
Any valleys should be examined for cracks or overspill.

 

[Stimpleton]

Thanks very much for your reply Vinn. Glad you don't think it looks like dry rot.

The tiles are indeed concrete. I thought it was a strange type of lining - very tough and inflexible, and it doesn't feel very breathable. Any idea if that sort of thing is likely to have been misused in the 60s or added later by a bad roofer? Thankfully the loft seems well ventilated, it always feels drafty and there have never been any signs of condensation at all, and maybe lucky it's over the living room rather than the kitchen. Do you think this felt poses a risk of condensation under the tiles? Also when you say it needs full support what exactly do you mean?

If someone has previously probed the lath, does that suggest there was a leak there in the past and they were checking for wet rot? I am hoping maybe the rot is just an historic problem as it does feel dry. In any case I will get the area checked out of course and the chimney flashing which is a few feet above it.

Thanks again.