Two questions about my roof (vent pipe and possibly some sagging)

[lasix]

First question: I have builders doing some work in a room at first floor (under the loft) and, while they were taking down old plasterboard, it became apparent that the ceiling had previously been over-boarded. The top layer of plasterboard had clear and extensive water damage but the added layer is perfectly fine. In the loft I cannot see any sign of water damage on the rafters and joists (but it has also not rained lately). I got a bit suspicious so I've had a good look from the outside and I've realized that a bit of the roof actually looks like it is sagging (red area in picture attached). Should I be concerned about this or is it likely an historical problem and not really concerning?

Second question. The builder has removed the vent pipe so now there is just the remaining ventilation slate (see picture attached). The builder is planning to just cap it with something to prevent water the water from getting in. I am wondering, without the soil vent pipe inside, will this arrangement be stable or will it be moving a potentially be displaced in case of strong winds?

 

[Alastairreid]

The weathering slate would be better removed if it is redundant. You can get those tiles from reclamation yards. (Delta).
I cannot see any sag in the roof in those pics.

 

[lasix]

The weathering slate would be better removed if it is redundant. You can get those tiles from reclamation yards. (Delta).
I cannot see any sag in the roof in those pics.

Actually, how are the weathering slates fitted? Without the vent pipe inside, is there any risk of it being blown away and ending-up on someone's head. From the photos I've taken it seems like it's just on top of the slates with nothing really holding it in place.

 

[Alastairreid]

It won't blow away but is pointless having it if it is no longer in use, its basically a sheet of lead which goes under the top and over the bottom tiles, ..fixed with a couple of nails to the tile batten.

 

[Exedon]

Unless the soil pipe has been removed completely down to drain make sure drains are correctly vented elsewhere.
Sticking a aav on stack and leaving drain unvented will not do!

 

[lasix]

It won't blow away but is pointless having it if it is no longer in use, its basically a sheet of lead which goes under the top and over the bottom tiles, ..fixed with a couple of nails to the tile batten.

Regarding the roof, it appears that it is made of two different kinds of tiles. As you said, one is the Redland Delta, the other one looks like a flat tile between the two Redlands. Can you identify which type is it?

 

[Alastairreid]

Redland stonewald