Roofing advise needed

[abg]

Evening,

 

New to the forum and so thanks in advance for any info provided.

 

Trying to deal with a leak at my fathers house.  The leak has been coming from this hip end of the roof and, I think, from the dislodged arris hip tile. There are many other tiles that are broken, dislodged etc. 

 

All the arris tiles are fixed well and are loose but not to the point of falling off.

 

A few questions:

I presume that some of those hips tiles are incorrect as they are of a different shape and just look wrong? - big gaps. Maybe bodge job done at some point.

 

I am tempted to remove all the tiles on the hip and replace for new.  However, as one of the photos shows, there is no permeable/impermeable layer under the tiles nor battens. The boarding slats appear to be angled to allow the tile nibs to sit on.

 

Should I just retile with new tiles over these boards or should I install a permeable layer over these boards?  Not sure I want to remove the boards and replace with flat surface and battens as they are in good nick. (At least from within the loft they look good)

Final question - these sort of arris hip tiles - should they be cemented down?

 

Thanks.

 

Andrew