Green Building Forum - Insulation and ventilation around stench pipe in bathroom

Insulation and ventilation around stench pipe in bathroom

greenfinger — Thu, 30 Mar 2023 13:48:55 +0100

Hi

Iâ€™m in the process of insulating my bathroom. Iâ€™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, Iâ€™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. Iâ€™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?

Thatâ€™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 doesnâ€™t need to be top notch from an insulation point of view; itâ€™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 donâ€™t cause any hidden problems.

Many thanks

Insulation and ventilation around stench pipe in bathroom

djh — Thu, 30 Mar 2023 20:48:05 +0100

Presumably as the pipe goes through the roof it is an SVP (a soil ventilation pipe). If so it is open at the top and is full of external air, so very cold inside in winter. So:
Posted By: greenfinger- Should I insulate and seal around where the pipe goes through the ceiling and PIR?
yes. Use a lot of stretchy airtight tape (e.g. Siga Rissan) in short bits around it.
- Can I insulate around the pipe from floor to ceiling inside the boxing?

yes. Maybe use foil-faced mineral wool available for insulating pipes?

I suppose you could make a drain around the base of the pipe and lead it to a small hole in the box at floor level to provide an escape route for condensation, if you were especially paranoid.

Insulation and ventilation around stench pipe in bathroom

philedge — Thu, 30 Mar 2023 20:57:18 +0100

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

Insulation and ventilation around stench pipe in bathroom

djh — Thu, 30 Mar 2023 21:18:06 +0100

Posted By: philedgeRemove the pipe and fit a Durgo valve?

He would need to check whether there was some alternative SVP somewhere that removed the need for this one. You can't have AAVs everywhere, at least some have to be SVPs. But yes, all our internal soil pipes have AAVs and we have one external SVP that has nothing draining into it. It just looks like our downpipes.

Insulation and ventilation around stench pipe in bathroom

DavidND — Fri, 21 Apr 2023 09:48:36 +0100

Posted By: philedgeRemove the pipe and fit a Durgo valve? No insulation or condensation to worry about

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.

Insulation and ventilation around stench pipe in bathroom

Simon Still — Fri, 21 Apr 2023 10:56:25 +0100

Posted By: DavidND
Posted By: philedgeRemove the pipe and fit a Durgo valve? No insulation or condensation to worry about

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.

I dont' think this is correct. Regs allow use of AAVs and have done for many years. Our house has one and have had no issues (so far) after 8 years.

https://bpfpipesgroup.com/media/62299/Air-admittance-valves-for-domestic-properties.pdf

only time we've had any smell issues has been traps drying up after a long period of non-use (I think low profile shower or basin drains are normally the culprit). That was just as much of an issue (ie not much at all) in the previous house with traditional vent pipe. And actually I think it was more of an issue there - on very windy days I think you sometimes get enough pressure to disturb trap water.

Insulation and ventilation around stench pipe in bathroom

djh — Fri, 21 Apr 2023 12:34:37 +0100

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.

Insulation and ventilation around stench pipe in bathroom

tony — Fri, 21 Apr 2023 13:22:59 +0100

Seal all gaps and cracks, fully insulate the pipe then box in

Insulation and ventilation around stench pipe in bathroom

philedge — Sat, 22 Apr 2023 18:19:08 +0100

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

Insulation and ventilation around stench pipe in bathroom

djh — Sun, 23 Apr 2023 10:27:09 +0100

Posted By: philedgethe physics of it makes much more sense

Could you explain how allowing gas to enter the drains but not leave it makes sense?

Insulation and ventilation around stench pipe in bathroom

greenfinger — Sun, 23 Apr 2023 16:02:27 +0100

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

Insulation and ventilation around stench pipe in bathroom

greenfinger — Sun, 23 Apr 2023 16:05:39 +0100

...

Insulation and ventilation around stench pipe in bathroom

Dominic Cooney — Mon, 24 Apr 2023 12:18:25 +0100

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.

Insulation and ventilation around stench pipe in bathroom

Dominic Cooney — Mon, 24 Apr 2023 12:24:08 +0100

I think this is the one I used, I have also put one in for the bathroom extractor outlet.

Insulation and ventilation around stench pipe in bathroom

Dominic Cooney — Mon, 24 Apr 2023 12:27:25 +0100

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

Insulation and ventilation around stench pipe in bathroom

philedge — Mon, 24 Apr 2023 13:26:03 +0100

Posted By: djhCould you explain how allowing gas to enter the drains but not leave it makes sense?

But it can vent! There's a bit of air that maybe drawn in through the Durgo valve when the toilet is flushed and an equivalent amount vents through the pipework to the septic tank.

The physics making sense that I was referring to was using a Durgo valve on a dead end bit of pipe rather than having a cold SVP running through the house. As the SVP is open both ends its easy to see a continuous draft of cold air running through the house inside the pipework. Unless the pipework connected to the SVP is insulated along its full length, its easy to see that the house will warm the SVP and the air inside it then start a convection current continuously drawing external air into the uninsulated pipework and cooling the house. Seems to me that a Durgo valve stops that and keeps the waste pipework warm??

Insulation and ventilation around stench pipe in bathroom

djh — Mon, 24 Apr 2023 16:15:07 +0100

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.

Insulation and ventilation around stench pipe in bathroom

philedge — Mon, 24 Apr 2023 20:03:27 +0100

That's a difference in our terminology then. I dont consider underground waste pipes to be a SVP. To me a SVP is the pipe that allows air into the system behind the soil/water when you flush a toilet. Typicallly sticking up through the roof or running up the side of older properties. Sorry for the confusion

Insulation and ventilation around stench pipe in bathroom

philedge — Mon, 24 Apr 2023 20:07:00 +0100

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

Insulation and ventilation around stench pipe in bathroom

Dominic Cooney — Mon, 24 Apr 2023 21:55:35 +0100

Also you can reduce to 2â€ for the vent bit up to the roof, it can make it easier to route.
I routed it inside the roof insulation up the slope of the roof, to a ridge tile vent, in the last place.
Although on the barn conversion here we fitted an AAV
But then the highest/furthest point on that drain run is the one in the farmhouse, where I have fitted the tile vent
(Replacing a 2â€ pipe that just stuck out through the roof!)

Insulation and ventilation around stench pipe in bathroom

djh — Tue, 25 Apr 2023 11:12:51 +0100

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

Are you sure?

AD H says (p11 sect 1.32) "Sizes of stack ventilation pipes â€“ 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."

Insulation and ventilation around stench pipe in bathroom

Dominic Cooney — Tue, 25 Apr 2023 14:03:06 +0100

No I didn't check.
Perhaps it has changed recently?, the one in this house is 2" and has been thus since 1975 without incident.
Also I seem to recall it being acceptable around 2010/2012 when we did the last place, but I can't remember if it was the plumber that gave me the useful tip, or the Building Inspector. It could have been outdated then though!

Insulation and ventilation around stench pipe in bathroom

djh — Tue, 25 Apr 2023 16:15:41 +0100

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.