Is this slate roof ‘porous’ ?

[Donna M]

Hi all, 

This slate roof is 150 yeas old. The structure appears to be sound and well built, the rafters are wet when it is stormy weather, tiles seem to get wet at corners of tiles as in picture. Is this porous slate or condensation, or something else ? Any advice on next steps is a reroof inevitable? 
 

Thanks all

 

D

[markc]

I reckon this is just wind blown water with you saying stormy weather. 

[Redbeard]

10 hours ago, Donna M said:

the rafters are wet when it is stormy weather, tiles seem to get wet at corners of tiles as in picture.

 

Is this a problem over the whole roof, or in discrete areas only?

 

I suspect, given your description, that it is rain blowing up the laps. Although I suggested in another recent thread that sarking felt is not always 'noticeable by its absence' this may be an exposed situation where it would help. It's a bit older than mine, but not much, and I would have little hesitation re-laying at least 60% of my slates as a new roof . I have seen an example in an area of very high industrial pollution where natural slates resembled 'porridge', but if your slates look OK from the top it may well be 'cause they are.