Valley problem

[Eddie largo]

Diy guy here with a roof repair question. I live in midterrace with double roof ( ie there is a valley running along the centre of the whole terrace) . The valley leaks meaning wall plates and bottom of joists have rotten. I’ve replaced the rotten timbers but now looking to fix up the valley. I’ve been up there and this is what it looks like ( see attached). Seems that the leak comes from where the valley meets the bottom of the tiles. Any thoughts on best fix for this???? Thanks!

 

[tell80]

OP,
You have quite a problem that could be an expensive problem for you as a single householder in that terrace.
Could you somehow arrange a co-operative effort between all the householders in the terrace?
Which roof is your property?
How you can you have "replaced the rotten timbers" without lifting the valley trough material and a few courses of slates?

The fibre cement slates & the natural slates are in reasonable condition excepting at chimney stacks and roof joins where things get a bit higgledy-piggledly.
The trough material is inadequate, and appears to have splits or joins repaired with silicone/sealant.
The material should be much wider and, with Mfr's advice, rolled out as one piece if possible.
Its difficult to determine where the valley falls, how its discharging water.

The valley trough upstands should turn up the roof - and Eaves Tray Felt Support trays - should go over the turned up upstand & project over the valley trough - with the roofing felt going over the support trays - the first course of slate comes over the above & projects, say, 20mm over the valley trough.
Roughly speaking what I've described is how support trays work over conventional house gutters.

To do a proper job then all the roofs will have to be disturbed and worked on.
There's quite a bit of other work needs doing such as the stacks and their flashing - and roof joins, probably lots of rotten roofing timber replacements also needed?

Back to work for now but fwiw I'll be back this evening .