'Visqueen' Roofing Underlay? Spalled Tiles / Roof Replacement

[machineage]

Hi all!

So, the roof on my Mum's Edwardian semi is in need of repair. Around 40 years ago, in previous ownership, the middle section of the roof was replaced. This section has black felt underlay, and the clay tiles all look to be in excellent condition, with no signs of spalling that I can see.

However, around 30 years ago, the areas of the roof each side were replaced, and it’s here where the problems exist. The old tiles & laths were removed, and what looks like plastic visqueen was laid, and topped with some of the old tiles and some reclaimed tiles. A large proportion of these tiles are now spalling, requiring the guttering to be periodically cleared.

My question is regards the ‘visqueen’ plastic underlay, is this acceptable practice for a roof on a property of this period, or should it all be ripped up and a more suitable breathable felt laid instead? There are no signs of damp or condensation in the roof space, and the rafters are solid & dry.

It is our intention to replace the tiles on these failing areas with tiles that match those on the good middle section to homogenise the appearance.

I’ve enclosed some photos.

Thanks!

Aerial view, showing the good middle area and the areas each side requiring replacement

Good middle section of the roof with black felt

Areas of roof requiring replacement with plastic 'visqueen' underlay

 

[datarebal]

it is simply a non breathable underlay. It was meant for the purpose it has been used for. I think Geof Capes advertised it.
the other sides are bitumen based 1f none are breathable.

 

[machineage]

@datarebal Thanks for that.

So would it be acceptable to leave both types of underlay in place if they are in good order?

Not sure what state the laths are in as yet.

Thanks again

 

[^woody^]

If the replacement tiles were reclaimed, then age of those tiles are most likely the problem, and nothing to do with the underlay.

 

[datarebal]

The underlay would be ok but is getting older .
If the tiles are off I'd fit new underlay too