Rear Extension - Cast Iron Soil Vent Pipe

[builditandtheywillcome]

I am in the process of planning my rear extension, i live in a terraced house where the cast iron soil vent pipe runs down the back of the house. In terms of an extension, some of the neighbouring properties have a mixed approach to retaining the SVP, some remove altogether (internal SVP not a viable option for us) whilst most build up to the underside of the key junction with the first floor WC. I have attached the model i am working on to give an indication of the area (in red).

My question is, in terms of waterproofing the roof, if i aimed for a 150mm lead flashing along the length of the roof junction with the house, is there a viable approach to a water proofing detail for where the roof meets the down pipe that is fixed to the rear wall? (i.e. no chance to get a waterproof collar around it)

 

[Notch7]

The difficulty is getting flashing chased in behind the soil pipe where its quite close.

To seal the pipe, its possible to run fibreglass up the pipe and then fit a split boot down over to shed water away from the junction.

Its all a bit awkward, but doable.

If there is a junction in the soil pipe just at the same height as the roof, its possible to box it out in ply, then fibreglass.

Dektite do various retrofit options

https://www.roofingsuperstore.co.uk...ipe-flashings/dektite-retrofit-flashings.html