Hi

I’m in the process of insulating my bathroom. I’ve taken the plasterboard down and put PIR between the rafters and joists, with more PIR beneath, perpendicular. We have a cold roof. The bathroom is more skeilings than ceilings. In the rafters, I’ve left a 50mm air gap between the topside of the PIR and the roof felt.

In the corner of the room there is a sewage/stench pipe from floor to ceiling and through the roof. I plan to box this in. I’m a bit confused about how best to tackle the stench pipe from a insulation and ventilation point of view... Presumably it will form a thermal bridge?

- Should I insulate and seal around where the pipe goes through the ceiling and PIR?
- Can I insulate around the pipe from floor to ceiling inside the boxing?

That’s what I had planned to do, but I then got confused as to whether this could cause problems with condensation or anything else on the pipe seeing as part of it is outdoors? The solution doesn’t need to be top notch from an insulation point of view; it’s an old house which will always have compromises. But with the pipe being out of site once boxed in, I want to make sure I get it right and don’t cause any hidden problems.

Many thanks

Remove the pipe and fit a Durgo valve? No insulation or condensation to worry about

<blockquote><cite>Posted By: philedge</cite>Remove the pipe and fit a Durgo valve? No insulation or condensation to worry about</blockquote>

Sorry, but PLEASE do not fit an AAV. The pipe has two functions, taking stuff away and venting 'malodours' to outside. Unless you have a vent within 3 meters of that one leave it open otherwise the risk of those malodours coming out in your bathroom are very high - and so very unpleasant.

In terms of insulating the space, I have used insulated plasterboard to box in my soil & vent pipe. Its now very much warmer and less noisy too.

There's a recommendation (see p11 of the BPF Pipes doc) that there be an SVP (i.e. an open pipe) at least every ten houses. So at a minimum greenfinger needs to check that his SVP isn't one of those required before converting it to an AAV. I don't think there's any requirement for an SVP every 3 m! ? We took the view we were a fair distance from everybody else so put one SVP up.

With regards to drying traps, yes we try to go around every month and use taps etc to refill all the traps. Not a big problem if we forget. I suspect the MVHR dries the traps more quickly with lower RH.

Posted By: DavidNDSorry, but PLEASE do not fit an AAV. The pipe has two functions, taking stuff away and venting 'malodours' to outside. Unless you have a vent within 3 meters of that one leave it open otherwise the risk of those malodours coming out in your bathroom are very high - and so very unpleasant.

We've had 2 Durgo valves in the house and no external SVP for over 20 years with no issues. They're fitted in the 2 upstairs bathrooms but none fitted to the ground floor bathroom or granny flat. No idea if that complied/complies with regs but the physics of it makes much more sense than having a large cold pipe running into the house

Thanks for all the replies and sorry for taking so long to get back to this after writing the OP. Other things got in the way!

Some further info...

There's no other vents in the house, as far as I know. But we are on a septic tank and there is a vent on that. I presume that this is something entirely different but mention it on the off chance that it fits into the whole scheme of things I'll add a photo below.

We don't have any neighbours.

I should also add that the boxing will be very tight to the pipe, and so will only allow for a very small amount of insulation. The bathroom is small, and the pipe runs very close to the side of the toilet. So options are limited.

We've been in the house for four years and not had a problem with the pipe to date. But that's been with the pipe just "as is". It was the boxing in, the addition of (albeit small) amounts of insulation around the pipe, and the additional insulation to the ceiling itself, which I thought could potentially change things enough to cause an issue. Condensation is by far more my concern than cold.

If I can replace for an AAV then all the better by the sounds of it. The roof would also look better without the pipe sticking out of it. But I guess I would also need to factor in the requirements form the other WCs in the house?

Many thanks

Posted By: greenfingerThe roof would also look better without the pipe sticking out of it.

You could go for a tile vent on the roof in this situation. That's what I did with ours, as it was the highest/furthest point from the Septic Tank. Looks better on the roof and still performs the same function.

You seem to be able to get them to suit pretty much all tile types and colours.

Exactly, you didn't say that it works IFF you have an open SVP elsewhere - specifically on the septic tank in your case.

And yes, obviously a pipe wholly within the heated volume stays warm, whilst one that penetrates between heated and unheated areas doesn't.

Forgot to add theres no vent pipe on our old brick built septic tank, just loose fitting covers

Posted By: Dominic CooneyAlso you can reduce to 2” for the vent bit up to the roof

Are you sure?

AD H says (p11 sect 1.32) "Sizes of stack ventilation pipes – stack ventilation pipes (the dry part above the highest branch) may be reduced in size in one and two storey houses, but should be not less than 75mm."

I remember the 75 mm/3" from when we built in 2013 and at that time I believe it had to be a metal pipe, but most types of plastic now seem to be acceptable.