House solely on AAV's?

[Moonshine]

My house design is that all SVP's are on AAV's and not vented to the external.

 

I met with my Architect today on site, and he wasn't sure if building control may ask for a vent.

 

Can anyone clarify (with references) that a house foul system can be vented purely by AAV's and don't need external vents.

[Conor]

Been through this as well, all AAVs ok for my BC guy

 

[joth]

My very rough understanding:

it's fine for all the "inside the house" vertical stacks to be purely on AVVs, so long as the horizontal drain they feed down into has a open-to-air vent at its furthest point from the main sewer. Typically this is done by extending the horizontal drain right through under the house and out the other side. The open vent can be down in the garden somewhere or whatever.

But different BC might see it differently.

 

We were going to do exactly this, but my main contractor removed the vented extension and got the architect to approve the change,  and then poured the slab without telling me (this was last April, and I was bed ridden and in quarantine with 'rona). Their argument was because nothing was feeding water regularly into the open vented end, it would slowly get blocked up with "back splatter" at the point the furthest upstream vertical stack drops into it. They debated swept bends, but never considered the obvious option that our extended pipe was going out to the garage and passed an outdoor tap we could have fed the drain down to it to keep it cleared out.
So anyway in the end we had to punch an extra hole through the roof so our final vertical stack can have the open vent on top. (They tried to charge me extra for that variation, so I asked for the money back on the horizontal pipe and foundation lintel they failed to install without my approval and they backed down ?)

 

 

Edited November 5, 2021 by joth

[Bitpipe]

We only have AAVs in our 4 WC house.

 

I was all set to put in a SVP but BC said it wasn't necessary as, given our neighbours all had SVPs, the sewer system would be well enough ventilated.

 

Saved what could have been an awkward penetration on a flat roof and a cold bridge on our passive house.

[Temp]

I don't think there is anything in Part H that requires an open vent. The nearest I can find is para 2.18 but read it carefully as it says only drains that have a water trap must have an open vent. Most houses don't have water traps anywhers in the drains.

 

Some BCO want the furthest stack from the sewer to be open vented and all others in a house can be AAV.

 

Also found this..

https://www.bpfpipesgroup.com/media/29598/Air-admittance-valves-for-domestic-properties.pdf

 

In a multiple housing situation, if all houses were fitted with an AAV, there is a risk that flows in underground drainage could create excessive back pressures on each connected dwelling. Evidence of this would be ‘bubbling’ and rising water levels in WCs and other appliance traps. To manage this risk, it is recommended that the house closest to the main sewer, i.e. the first house, and every subsequent 10th  house is also installed with an open stack vent. This is shown schematically here.

 

That implies open vents aren't mandatory on every house.

[SuperJohnG]

10 hours ago, Conor said:

Been through this as well, all AAVs ok for my BC guy

 

I'm working on this basis also. Bc seemed fine in call about it.

[Bitpipe]

12 hours ago, Temp said:

I don't think there is anything in Part H that requires an open vent. The nearest I can find is para 2.18 but read it carefully as it says only drains that have a water trap must have an open vent. Most houses don't have water traps anywhers in the drains.

 

Some BCO want the furthest stack from the sewer to be open vented and all others in a house can be AAV.

 

Also found this..

https://www.bpfpipesgroup.com/media/29598/Air-admittance-valves-for-domestic-properties.pdf

 

That implies open vents aren't mandatory on every house.

 

Yes, I remember the BCO quoting the 1:10 rule also.

[Thorfun]

this is an interesting subject for me as I've started thinking about it. didn't I read somewhere on this forum that you can have the open vent on the sewage treatment plant and have all AAVs in the house?

 

Our BCO is visiting site on Monday so I'll chat with her about it anyway but I'm sure I read someone on here had that.

[Nickfromwales]

12 hours ago, Bitpipe said:

Yes, I remember the BCO quoting the 1:10 rule also.

Pedantic ones will quote 1 in 5, but if you can visually demonstrate adjoining SVP's or that the you are not the end of line or at the crest of the sewerage network you should get an agreement that the SVP is not necessary.

But;

On 05/11/2021 at 14:14, Moonshine said:

Can anyone clarify (with references) that a house foul system can be vented purely by AAV's and don't need external vents.

No, we cannot. An AAV allows air in ( hence the name "air admittance" valve ), so these categorically will not and do not provide any such means of venting per-se.

 

AAv's are only a requisite where the invert from a discharging SVP to the 'manhole' aka IC is above 1300mm. Below that, there is not even a requirement for the AAV.

[Bitpipe]

On 06/11/2021 at 16:35, Thorfun said:

this is an interesting subject for me as I've started thinking about it. didn't I read somewhere on this forum that you can have the open vent on the sewage treatment plant and have all AAVs in the house?

 

Our BCO is visiting site on Monday so I'll chat with her about it anyway but I'm sure I read someone on here had that.

 

Yes, Jeremy H did it that way, vented at the plant to avoid a SVP in his house. 

[Thorfun]

4 hours ago, Bitpipe said:

 

Yes, Jeremy H did it that way, vented at the plant to avoid a SVP in his house. 

nice one. 

 

I did speak to our BCO about it today and she said you can do it but it's 'best' to vent at the head. and she said that again to reiterate it when I made the point about venting at the STP again. so I have taken the hint and will just vent out of the roof but we've agreed that I can use one of these slate vents (https://www.slate.uk.com/product/nature-vent/) which is a lot less obvious on the roof than a pipe or mushroom. I'll just have to make sure the penetration is well taped and sealed.

[Iceverge]

The big problem is it'll draft like a chimney and cool your nice house.

 

We used an AAV and vent at a seperate stack by the garage.

 

BTW if you don't want to go through the roof you can go horizontally through the wall with an elbow and a reducer to a 50mm waste pipe. 

[Thorfun]

35 minutes ago, Iceverge said:

The big problem is it'll draft like a chimney and cool your nice house.

 

We used an AAV and vent at a seperate stack by the garage.

 

BTW if you don't want to go through the roof you can go horizontally through the wall with an elbow and a reducer to a 50mm waste pipe. 

How big of an impact in reality will it have? Is there any data or have there been studies done? It all sounds so very doom and gloom!! What if the pipe that’s vented is insulated or boxed in and the boxing in insulated? Will the cold from the pipe move through the connected pipes and affect all other soil pipes? I’m struggling to fathom how it’s possible that one vented pipe can cause such an issue!

 

we did speak about venting sideways as well but that’s still a penetration and will surely have the same effect? 
 

one of our soil pipes is near the garage so maybe venting that one will have less of an overall impact?

[ProDave]

My real world experience.

 

I tried to avoid a vented stack through the house.  I had vented the in ground drain run at both ends, but the far end was at the static caravan, and BCO would not accept that the vent stack there was a permanent feature.  He would have accepted a vented stack from the ground drain up the end of the house on the outside but by this point that was concreted over so it would have been too much disruption to put that in place, so reluctantly I had to have a vented stack through the house.

 

That little bit of boxed in space through the utility room, indeed the plasterboard of that bit is about 1 degree cooler than the other outside walls.  Someone will no doubt calculate how much heat loss I am getting by a section of wall 2.4M high by 300mm wide being 1 degree cooler than it would be if the cold vent pipe was not there.

[Iceverge]

 

1 hour ago, ProDave said:

Someone will no doubt calculate how much heat loss I am getting by a section of wall 2.4M high by 300mm wide being 1 degree cooler than it would be if the cold vent pipe was not there.

 

Someone already has. 

 

https://www.elementalsolutions.co.uk/wp-content/uploads/2012/08/Heat-loss-via-internal-drainage-vent-pipes-full.pdf

 

1 hour ago, Thorfun said:

How big of an impact in reality will it have? Is there any data or have there been studies done? It all sounds so very doom and gloom!! What if the pipe that’s vented is insulated or boxed in and the boxing in insulated? Will the cold from the pipe move through the connected pipes and affect all other soil pipes? I’m struggling to fathom how it’s possible that one vented pipe can cause such an issue!

 

Reading the above study it looks like I was dramatic with my language. Just accept 20w extra heat load per soil stack or add 50mm mineral wool and forget all about it.  

 

 

1 hour ago, Thorfun said:

we did speak about venting sideways as well but that’s still a penetration and will surely have the same effect? 

 

Yes but it's better to avoid holes in the roof IMO. 

 

 

[Thorfun]

9 hours ago, ProDave said:

My real world experience.

 

I tried to avoid a vented stack through the house.  I had vented the in ground drain run at both ends, but the far end was at the static caravan, and BCO would not accept that the vent stack there was a permanent feature.  He would have accepted a vented stack from the ground drain up the end of the house on the outside but by this point that was concreted over so it would have been too much disruption to put that in place, so reluctantly I had to have a vented stack through the house.

 

That little bit of boxed in space through the utility room, indeed the plasterboard of that bit is about 1 degree cooler than the other outside walls.  Someone will no doubt calculate how much heat loss I am getting by a section of wall 2.4M high by 300mm wide being 1 degree cooler than it would be if the cold vent pipe was not there.

 

thanks Dave. our pipe will be behind a wall that runs through the larder and then goes in to the plant room in the basement and then out underground so I could actually do with that pipe cooling down those rooms! ? 

 

7 hours ago, Iceverge said:

Reading the above study it looks like I was dramatic with my language. Just accept 20w extra heat load per soil stack or add 50mm mineral wool and forget all about it. 

 

thanks for the study link and the summary. I'll be putting some Rockwool in between the studs of internal walls so I'm hoping that it won't make a difference for me, but if it does I will just accept the extra 20W of heating load.

 

7 hours ago, Iceverge said:

Yes but it's better to avoid holes in the roof IMO.

 

any particular reason for this? is it due to water ingress or some other factor? 

[joth]

7 hours ago, Iceverge said:

Reading the above study it looks like I was dramatic with my language. Just accept 20w extra heat load per soil stack or add 50mm mineral wool and forget all about it.  

 

Phew. When our vented stacked was forced into the design I raised this concern, our passivhaus consultant spoke with the building physics/thermal bridge consultant and they said it should not be a problem in practice. We filled the void with as much rock wool as it would take and haven't thought about it again really.

Upstairs it goes behind the ensuite, the master bedroom of which is pretty consistently the warmest room in the house, so I'm not stressing it. 

[Iceverge]

1 hour ago, Thorfun said:

any particular reason for this? is it due to water ingress or some other factor?

 

Yes water, it's very persistent!

 

 

[Bitpipe]

Mine would have had to penetrate a flat roof so I was very happy to avoid compromising the waterproofing, the thermal issues were never my concern TBH.

[Moonshine]

11 minutes ago, Bitpipe said:

Mine would have had to penetrate a flat roof so I was very happy to avoid compromising the waterproofing, the thermal issues were never my concern TBH.

 

this is exactly the issue i have, that it will be going through a flat roof if i had to have it vented.

 

There is an opportunity for the soil stack to gout of an exterior wall horizontally at high level but i really don't want to do that.

 

[Iceverge]

I know it looks naff but an old fashioned through the wall waste pipe and external stack would avoid both issues. 

 

 

[Dan F]

For those of you that used AAV's; what, if anything, did you do with these during airtightness testing? 

 

During depressurization they will naturally be closed, but during a pressuzation test surely there is a point where which they open and this results in leakage impacting results?  I can't find anything online about if they can/should be sealed during a pressuzation test.  Anyone else had any experience?

 

[Iceverge]

Our waste pipes were not finally installed by the time we did our test so I just taped up what ones there were. 

[Temp]

3 hours ago, Dan F said:

For those of you that used AAV's; what, if anything, did you do with these during airtightness testing? 

 

During depressurization they will naturally be closed, but during a pressuzation test surely there is a point where which they open and this results in leakage impacting results?  I can't find anything online about if they can/should be sealed during a pressuzation test.  Anyone else had any experience?

 

 

Its the other way around. AAV open to let air into the pipe and close to prevent sewer gas leaking into the room.

[Dan F]

41 minutes ago, Temp said:

Its the other way around. AAV open to let air into the pipe and close to prevent sewer gas leaking into the room.

 

It works via pressure-differential though.  It can open to admit air when a toilet flushs and the pressure in the drainage is lower than in the house where AAV is installed.

 

It's therefore logical that when you pressurize the house, as part of an air-test, that this pressure-differencial is replicated and the AAV opens, resulting in air leakage.  Clearly, with a test that depressurizing the house the AAV's will stay closed.