Soil pipe modifications

[aroberts34]

The soil pipe from my 1st floor toilet is currently arranged as shown in 'current arrangement' sketch, attached. There is an original cast iron swan neck which is half embedded in the concrete roof of the extension. This means that the roofing felt has been sort of draped over the pipe as it intersects the roof. Not very good, difficult/impossible to seal properly, and it leads to a localised patch of dampness inside. Interestingly, the neighbours houses seem to have a similar arrangement.

I want to raise the swan neck so that it is clear of the roof, allowing me to repair/seal the roof properly. To do this I would remove the cast iron swan neck and replace with some PVC piping as shown in 'desired arrangement'.

1. Can this be done without having to mess around with the toilet tee and other piping above? The new piping would be push fit, can I get away with pulling the joints out by a few mm (once in position) to allow the final connection to be made?
2. Is it likely that the roof is meant to support the piping? There are a couple of brackets on the cast iron vertical section (not shown on sketch) although they seem a bit degraded. How likely is it the whole thing would collapse if I raised the bends up like I want to?

 

[Hugh Jaleak]

Cast weighs an absolute ton, be very careful when dismantling any of it, the more there is above you, the more weight to come down.

You may well find the cast is in poor condition where it is embedded in the roof, so allow for that when taking apart. Should be able to join onto vent section above by using a slip coupling, rather than trying to force things together.

 

[aroberts34]

Thanks, slip coupling was the answer I needed. I started another thread regarding my next question about how to dismantle the cast iron/lead socket joint.