Boxing in Vent Pipe

[regsmyth]

I'm redoing the cloakroom.
There is a 3" vent pipe in the corner going up through the ceiling and out through the roof.
When I removed the old boxing in, the pipe was "lagged" with glassfibre. The pipe was black with mould.
What is the standard detail here - to insulate or not?
The waste pipe from the basin was also boxed in - again stuffed with glassfibre. Is this standard practice?
Thanks for any advice.

 

[pinenot]

Plastic or metal vent pipe?

 

[regsmyth]

It's plastic...

 

[pinenot]

Interesting, normally plastic vent or stench pipes as we call them, don't tend to form condensation i.e. turn black with mould, if mould is indeed what it is of course. Not normal is the answer to your question in my experience. As a stench pipe doesn't carry water it's not normally subject to condensation and as no waste water is coming down there's no need to lag it for acoustic reasons, however you may want vent the pipe box to prevent any repeat of the black 'whatever'...pinenot

 

[regsmyth]

Thanks for the info. I will leave it clear. I suspect it was condensation from a very poor boxing in effort, and the glassfibre got saturated and never really dried out. In winter I suppose the pipe surface would be quite cold. But that's a guess. It could also be leaking from the roof tile above or at the felt where it penetrates.
I'll check it out next time it rains.
Thanks again.