Sewer pipe air vent question

[AverageDIYerEssex]

Hi all.

Do I am fitting a new bathroom upstairs and changing the position of the toilet. Long story short I am loosing the old soil stack that serviced this bathroom and plumbing it into a now disused downstairs WC hole in the ground (which leads to the same sewer connector)

I have just uncovered the old stack and found it collects the WC and then carries on straight up into the loft to vent.

My questions are...
1. Do I need to have an air vent on the new stack?

2. Can I use an air admittance valve instead and if so how high does it need to be above the toilet level and will it leach smells/gasses into the room.

3. If I have to go up into the loft with a new stack to give an air vent, does it need to be in a straight line with the stack or can I take it off a bend further along the line?

4. If I do it the way as per the image below... does it need to be 4" pipe or can it be smaller?

Thanks in advance.

 

[AverageDIYerEssex]

Like this...

 

[Ollyfp]

I've used AAVs in two properties with no issues at all. As long as the air admittance valve is securely attached and is at least 1m above the highest appliance, it should be fine.
I'm not a plumber though!

 

[Ollyfp]

Stick to 4" and you can put a dog leg in if you need to.
Hope you signed that picture!

 

[dilalio]

Is there a vent pipe elsewhere on the property? If so, where?

I always think a vent is best but in the setup in your sketch, as long as air can be pushed out the sewer in front of the volume of flushed water, and air pulled in behind it, it should be OK.

But it's hard to really make a decision without seeing it first hand.

 

[AverageDIYerEssex]

Is there a vent pipe elsewhere on the property? If so, where?

I always think a vent is best but in the setup in your sketch, as long as air can be pushed out the sewer in front of the volume of flushed water, and air pulled in behind it, it should be OK.

But it's hard to really make a decision without seeing it first hand.

Been up in the loft to look at the current setup as I thought the soil pipe was vented to outside through the roof tiles but it just has an AAV on it in the loft so think I'll just do the same. I thought it was going to be grief running the new one to the old roof tiles opening but if it's just an AAV I might as well do it properly.

 

[AverageDIYerEssex]

Is there a vent pipe elsewhere on the property? If so, where?

I always think a vent is best but in the setup in your sketch, as long as air can be pushed out the sewer in front of the volume of flushed water, and air pulled in behind it, it should be OK.

But it's hard to really make a decision without seeing it first hand.

Actually, what's your thoughts on using maybe a 50mm pipe with a 50mm AAV on it?

It's just I'm going to try and recreate the image below and would be good if I can use a 50 and run it where the red line is so it don't take up too much space inside the cupboard part.

 

[Hugh Jaleak]

Couple of points to consider. Soil Stacks should have a Long Radius rest bend at the bottom, to allow the falling waste to flow gently round into the drain, the old ground floor WC may well have a sharper bend at the bottom, which could cause issues with noise and compression of air. If there are any other connections lower down, be careful these aren't compromised.

Bends in the wet part of the stack are best avoided where possible. Dry section isn't so critical, just ensure no dips or low spots in the run. What is the reasoning behind installing a new stack and not using the existing?

Advise at least one vent on the property. If you must use an AAV, then they do exactly what it says on the tin, they let Air in, they wont let odours out unless valve fails and sticks open. Need to be fitted above the spillover level of the highest appliance on the stack, (usually the Basin.) Can reduce down to 82mm, I wouldn't go any smaller personally.

 

[AverageDIYerEssex]

Couple of points to consider. Soil Stacks should have a Long Radius rest bend at the bottom, to allow the falling waste to flow gently round into the drain, the old ground floor WC may well have a sharper bend at the bottom, which could cause issues with noise and compression of air. If there are any other connections lower down, be careful these aren't compromised.

Bends in the wet part of the stack are best avoided where possible. Dry section isn't so critical, just ensure no dips or low spots in the run. What is the reasoning behind installing a new stack and not using the existing?

Advise at least one vent on the property. If you must use an AAV, then they do exactly what it says on the tin, they let Air in, they wont let odours out unless valve fails and sticks open. Need to be fitted above the spillover level of the highest appliance on the stack, (usually the Basin.) Can reduce down to 82mm, I wouldn't go any smaller personally.

Thanks for you reply and advice.

1. The noise shouldn't be a problem as the drop part from the first floor to the WC hole (for want of the correct terminology for it) is behind a cupboard so hopefully will be ok. As for air compression... ‍ This line goes on its own all the way out to the 3 way inspection chamber so hopefully no compromise.

2. I had to bend it a little owing to where it came though on the first floor to bend backwards behind the cupboard and into the WC hole. I did however make sure that it was at the correct fall ratio on the horizontal section so hope it'll be ok.

The old stack runs down at the back of the house (inside) but goes straight down in front of our new bifolds we had fitted. So we literally have a poo pipe in the middle of the doors which isn't ideal lol. So basically that whole run needs to go. Because I also moved the WC downstairs it meant that hole was now free so after having to completely reconfigure the upstairs bathroom I devised a route for the new stack so it can go into the old WC hole.

3. Our house actually has 2 stacks plus the WC hole. One at the front which runs into a 3 way inspection chamber and the back (which I'm talking about) and WC both go into a different 3 way inspection chamber. They then obviously both run down into the main sewer line. I am pretty sure the front stack will have an AAV in the loft like the back does but I imagine they'd both need one if they go to different chambers and are not connected no? If not brilliant and I'll do away with a vent for the new back one. But if I DO need it, would a length of 50mm pipe bossed or trunked into the wet horizontal 4" pipe with an AAV and obviously above minimum requirements work? Or does it have to be 4" too?

 

[Madrab]

As suggested - if all the other stacks have AAV's on them the it would be advised to have one open vent on the system. Drains/sewers/stacks need to breathe and that means to allow positive and negative pressure to be equalised at at least one point on the system. If there isn't then it could cause issues with free draining of the waste system or major issue if the system become blocked.

It also needs to be understood where you system is on the combined drain system and what every other connected system uses. A main drain really needs to have a vent at the head of the run. If yours is and the other connections are all using AAV's then the main drains can also be affected. It can get quite complicated.

A 50mm isn't ideal, the rule of thumb is the vent should be at least half the size of the the pipe it supports, ergo the 82mm suggestion.

 

[AverageDIYerEssex]

A 50mm isn't ideal, the rule of thumb is the vent should be at least half the size of the the pipe it supports, ergo the 82mm suggestion.

damn I totally misread this. I thought it was talking about height of the AAV. I wondered why I didn't understand the measurement lol.

I'll probably just keep it 4". I will reuse the old length of pipe so won't cost anything.

 

[Ollyfp]

We had a through-roof vent on our stack pipe and sewer gas wafted in through our bathroom window like Bisto when the wind blew in a certain direction, so I cut the pipe down to 1m above the upstairs loo and bunged an AAV in there (it terminated in the eaves). Anyway, that was 4 years ago and I have no problems to report.

 

[AverageDIYerEssex]

We had a through-roof vent on our stack pipe and sewer gas wafted in through our bathroom window like Bisto when the wind blew in a certain direction, so I cut the pipe down to 1m above the upstairs loo and bunged an AAV in there (it terminated in the eaves). Anyway, that was 4 years ago and I have no problems to report.

Sounds ideal. Thank you.

 

[dilalio]

We had a through-roof vent on our stack pipe and sewer gas wafted in through our bathroom window like Bisto when the wind blew in a certain direction, so I cut the pipe down to 1m above the upstairs loo and bunged an AAV in there (it terminated in the eaves). Anyway, that was 4 years ago and I have no problems to report.

Doesn't mean it will be the same on another property.
Soil vent pipes should go up above the eaves and away from any velux windows.

 

[dilalio]

Time and again on this forum, an AAV is viewed as a tidy and easy solution to disposing of SVPs.
Sewers need to breathe OUT as well as IN!
I have been to hundreds of drainage issue jobs where replacement of SVPs with AAVs has been the cause.
And I'm not a below-ground plumber/drainage expert, like some of my peers on here are.