Soil stack passive house

[dnoble]

I realise I should of though about this earlier but are there any passive house implications around soil stacks?

Aesthetically an internally vented one in the loft with an AAV would be preferable. Is this allowable/advisable in a passive house. Intuitively it would seem to be less likely to cause heat loss. 

 

[ProDave]

Speak to your BCO

 

A stack with an AAV is allowed, BUT the drain run will have to be vented somewhere to the satisfaction of your BCO.  I didn't realise this in time and the only thing he would have accepted was an external stack up the gable end, and it was too late them I had already concreted the parking area alongside the house so too late to lay a branch to serve that external vent stack.

[Jeremy Harris]

31 minutes ago, dnoble said:

I realise I should of though about this earlier but are there any passive house implications around soil stacks?

Aesthetically an internally vented one in the loft with an AAV would be preferable. Is this allowable/advisable in a passive house. Intuitively it would seem to be less likely to cause heat loss. 

 

 

We have an internal stack with an AAV on top.  No problem at all with the BCO, he just wanted a diagram showing what I planned to do and an assurance that the AAV could be easily accessed if it needed replacement.  The diagram I sent him was this one:

 

Elevation - Section showing foul drain stack - A4.pdf

 

In addition, you have to ensure that the external foul drain is vented, in our case that's via the treatment plant, but a low level vent, perhaps hidden in a hedge or flower bed, is acceptable.  Low level vents were (probably still are) commonplace in cities and towns, as well as on top of old septic tanks, and they rarely cause any problems.

 

Arranging the soil vent like this avoids the significant thermal bridge that a through the roof, or out the wall, vent pipe would present you with.

 

[dnoble]

That's brilliant, Jeremy I was hoping to do something similar. Hadn't realised it also needed external ventilation too so thanks for that additional

[joe90]

I have an internal AAV in our new build but the drain run goes past the house and  to the detached garage with a loo so I put the stack on the back of the garage.

[ProDave]

11 minutes ago, joe90 said:

I have an internal AAV in our new build but the drain run goes past the house and  to the detached garage with a loo so I put the stack on the back of the garage.

That was accepted because your garage is permanent.

 

I vented my stack at the end at the static caravan. My BCO argued the caravan was not permanent. I argued it had PP to remain as a work space. He argued some future owner might remove it. I argued if they do, then they should make provision to ventilate the drain then, he argued they would not.

 

I lost the argument so have a stack pipe through my roof.

[Jeremy Harris]

As a bit of additional info, I believe that @PeterStarck may have a low level external vent, and as his build is also a PassivHaus, he may well be able to confirm that external vents are acceptable when used i conjunction with an AAV on top of an internal soil stack.

[pdf27]

23 minutes ago, JSHarris said:

As a bit of additional info, I believe that @PeterStarck may have a low level external vent, and as his build is also a PassivHaus, he may well be able to confirm that external vents are acceptable when used i conjunction with an AAV on top of an internal soil stack.

We have a low-level external vent on our current (1920s) house, and the architects have previously stated that it's OK to continue using that for venting sewer gases - indeed strongly preferable to do so. From memory the statement was that on another project they'd modelled the high level vent to cost 1 kWh/m²/year of losses - not massive in heating bill terms, but a big deal if you're trying to hit a standard like Passivhaus which they were on that project.

[willbish]

My BCO has approved my drain plan with internal AAV's at the W/C's and a low level vent in the front garden, much like @JSHarris is describing.

 

Soil Plan.pdf

[Gone West]

12 hours ago, JSHarris said:

As a bit of additional info, I believe that @PeterStarck may have a low level external vent, and as his build is also a PassivHaus, he may well be able to confirm that external vents are acceptable when used i conjunction with an AAV on top of an internal soil stack.

That is correct. I have the main, 110mm,  AAV in the bathroom behind a false wall which houses the concealed cistern. I also have an external vent around 600mm high in a flower bed near the sewage treatment plant. The BCO didn't have any problems with the setup.

[dnoble]

Thanks for all this useful information.

That's a good solution, Peter, so there's no particular reason the AAV needs to be up in the loft space, it just be hidden behind a false wall (but obviously above soil pipe level), then?

[Jeremy Harris]

Ours is behind a partition wall in one of the bathrooms, but can be accessed by crawling along the eaves space.  You can get access doors to inset into a wall for things like this, too.

[Triassic]

But why do you need a vent in the first place, my sewage pipes are open ended in the septic tank, so why is a vent needed at the other end?

[Nickfromwales]

4 minutes ago, Triassic said:

But why do you need a vent in the first place, my sewage pipes are open ended in the septic tank, so why is a vent needed at the other end?

A vent is required to promote ventilation of the sewer gasses to atmosphere. 

[dnoble]

There's also something about negative pressure from flushing etc potentially disrupting the water in the U bends that prevents gas/smell entering the house from the drainage system

[Jeremy Harris]

47 minutes ago, Triassic said:

But why do you need a vent in the first place, my sewage pipes are open ended in the septic tank, so why is a vent needed at the other end?

 

My BCO accepted that the vent in the treatment plant, combined with the AAV on top of the stack, met the requirements.  The foul drain run is vented to atmosphere via the treatment plant vent (same as a septic tank vent in effect) and the negative pressure issue is dealt with via the AAV on top of the stack.

[ProDave]

2 hours ago, JSHarris said:

 

My BCO accepted that the vent in the treatment plant, combined with the AAV on top of the stack, met the requirements.  The foul drain run is vented to atmosphere via the treatment plant vent (same as a septic tank vent in effect) and the negative pressure issue is dealt with via the AAV on top of the stack.

Mine argued it needed venting at both ends so we are now where we are.

[Gone West]

6 hours ago, dnoble said:

That's a good solution, Peter, so there's no particular reason the AAV needs to be up in the loft space, it just be hidden behind a false wall (but obviously above soil pipe level), then?

The AAV should be above the highest drain point such as basin plug hole.

 

[Ed Davies]

5 hours ago, Nickfromwales said:

A vent is required to promote ventilation of the sewer gasses to atmosphere.

 

AIUI there are two vent functions needed:

 

1) to let gasses forming in the soil pipe out rather than them building up enough positive pressure to push past the water in the U bends which would be very unpleasant.

 

2) to let air in so that a big wodge of solids and liquids sliding down the pipe doesn't create enough negative pressure behind it to suck the water out of the U bends (actually, pushed by the atmosphere on the basin or whatever side) which would also be less than ideal.

 

A traditional soil vent pipe running up the side of the building and open above the gutter does both those functions. If you don't want that for any of various aesthetic or insulation reasons then the functions can be separated. A vent pipe further down the system does the first function. An air admittance valve inside the house lets air be sucked into the system for function 2 without letting any gases out (you really hope).

 

AAVs which let air in but not out  can also be used to break syphons in some systems. Confusingly, though, there's another sort of valve also called an AAV (but I can't remember what the letters stand for in that case but seem to remember the first A is “automatic”) which does exactly the opposite: it only lets air out (doesn't let it in and doesn't let liquid out - there's a little floating ball which seals it when liquid arrives) used to get rid of air in the top of the system. Typically used at the high point of solar thermal systems.

[Jeremy Harris]

The other AAV is an Automatic Air Vent, often called a bottle vent, which has an internal float and valve to let air out but keep water in, like this one:

 

[gravelld]

Yeah, we had one of those, don't let any crud get in them, ruined one Christmas...

Edited August 16, 2018 by gravelld

[Nickfromwales]

1 hour ago, Ed Davies said:

 

AIUI there are two vent functions needed:

The terminology is important. 

Vent = open to atmosphere 

AAV = sealed to atmosphere but opens to allow air IN if a vacuum occurs within the stack. 

?

[AndyRP]

I've struggled to find resources on this and found this thread v useful so I'll attempt to dust it off with a few questions. 

 

I'm renovating a small three storey (inc. converted loft) Victorian terrace. The existing brick inspection chamber is shared with our neighbour. We plan an internal AAV together with a separate ventilation stack for the reasons mentioned above. I'm in two minds between running it up the back of the house vs. putting it in the (v small) garden. 

 

1. Garden vs up the house seems primarily a trade off between smells in the garden or a big ugly pipe up rear of the house. Are there any other pros/cons I've missed. I think garden utility probably wins and I'll run it up the house. 

2. Of relevance to question 1, what size must the ventilation stack be? Part H does not seem clear on this. 1.32 allows the soil pipe to be 'reduced' in certain circumstances but this clause is clearly talking about the top of a standard discharge stack where only the portion above appliances is dedicated to ventilation. Since it's not explicitly addressed I guess there is an argument for 50mm as that is smallest discharge stack allowed in the case of low flow rates and a dedicated ventilation stack will have a flow rate of zero?

3. Can the separate ventilation stack go directly to the existing (shared) inspection chamber or does it need to be branched from the pipework upstream? 

 

I've attached the current ground floor plan that shows the relevant runs in case useful. 

A.30915.4.101.02_A3.pdf

[Temp]

I think Building regs specify 75mm ID (82mm OD?) as the minimum diameter for an SVP.

 

Normally building control like there to be one open vent stack. If there are 3 stacks planned they like the furthest from the sewer to be open vented. If you have some internal pipework that is slightly further they don't usually worry about it.