Moving inspection chamber. Any issues?

[flanagaj]

Below is the currently designed drainage run for our house.   I am contemplating moving the IC circled in red, simply because the invert level is 860mm below the FFL and these will be a PITA with regards to the footings.   



I am wondering whether I can instead take the soil pipe out the East side of the house at a level that works and then simply run with a 45 degree branch down into either a Y on the main branch (if allowed with regs) or run into another IC further along the branch to the east side.  Yes, it will mean that there is a short section which will exceed the 1/40 slope.  That section will be used for discharging a utility room and ensuite bathroom.

The only possibly complexity is around the fact that we are on a treatment plant and I have a feeling that gasses from the tank could in theory travel up the pipe and then up the first branch.  We are planning an SVP at the head of the stack, but I am not sure this would help if we had a branch. 

[Nickfromwales]

14 minutes ago, flanagaj said:

Below is the currently designed drainage run for our house.   I am contemplating moving the IC circled in red, simply because the invert level is 860mm below the FFL and these will be a PITA with regards to the footings.   



I am wondering whether I can instead take the soil pipe out the East side of the house at a level that works and then simply run with a 45 degree branch down into either a Y on the main branch (if allowed with regs) or run into another IC further along the branch to the east side.  Yes, it will mean that there is a short section which will exceed the 1/40 slope.  That section will be used for discharging a utility room and ensuite bathroom.

The only possibly complexity is around the fact that we are on a treatment plant and I have a feeling that gasses from the tank could in theory travel up the pipe and then up the first branch.  We are planning an SVP at the head of the stack, but I am not sure this would help if we had a branch. 

You can vent an STP in the landscape or at an outbuilding.

 

Gasses would travel to the end of the run and up / out the SVP at the far end of the run. You're panicking too much about that . A better drawing showing where the pipes rise inside the house would help, stating exactly what is connected and if they rise to 1st floor or not.

 

AAV's are not require on the ground floor unless the invert is at 1300mm or more btw, and a lot of BCO's are unfamiliar with that allowance.

[flanagaj]

41 minutes ago, Nickfromwales said:

You can vent an STP in the landscape or at an outbuilding.

 

Gasses would travel to the end of the run and up / out the SVP at the far end of the run. You're panicking too much about that . A better drawing showing where the pipes rise inside the house would help, stating exactly what is connected and if they rise to 1st floor or not.

 

AAV's are not require on the ground floor unless the invert is at 1300mm or more btw, and a lot of BCO's are unfamiliar with that allowance.

If a gas travelled along a pipe which then branched and one branch went off at a steeper gradient compared to the main run, I suspect it will take the pass of least resistance.   The branched run can have an AAV, but not a SVP as I don't want anything through the roof.  

 

I assume the svp is to allow air in so as to not create a pressure differential as the water moves down the pipe, but also for gasses to escape.

 

The ensuite is on the first floor

Edited 20 hours ago by flanagaj
Clarity

[Oz07]

No problem exceeding 1.40 with pvc pipe they removed max gradient from regs

[Nickfromwales]

10 hours ago, flanagaj said:

If a gas travelled along a pipe which then branched and one branch went off at a steeper gradient compared to the main run, I suspect it will take the pass of least resistance.   The branched run can have an AAV, but not a SVP as I don't want anything through the roof.  

 

I assume the svp is to allow air in so as to not create a pressure differential as the water moves down the pipe, but also for gasses to escape.

 

The ensuite is on the first floor

An SVP is exactly what it says, Soil Vent Pipe, so needs to go to atmosphere; either through the roof, or on an external façade finishing up higher than any openings etc.

 

STP's are not part of the network, so you have no obligation to vent the main sewer gasses, as per a network connection. You just need reliable and functional.

 

Do you have somewhere to vent the STP in the landscape (can be just a short stub above ground if far enough away to not cause nuisance) or rising up behind a shed or outbuilding etc.

 

10 hours ago, flanagaj said:

If a gas travelled along a pipe which then branched and one branch went off at a steeper gradient compared to the main run, I suspect it will take the pass of least resistance.

Methane is lighter than air, so will follow that principal. Static gasses should be prevented from building up, so if there is an SVP then even a minimal convection airflow will carry this gas up and out to atmosphere, nothing to do with the path of least resistance as none of the branches going into the house will have throughput of airflow, as you say they will all be capped off with an AAV.

 

10 hours ago, flanagaj said:

The branched run can have an AAV, but not a SVP as I don't want anything through the roof.

If you want an SVP to function as a vent, then a suitable location needs to be decided.

 

Ground floor WC's do not (typically) need an AAV or a vent etc.

 

2 hours ago, Oz07 said:

No problem exceeding 1.40 with pvc pipe they removed max gradient from regs

Ok over short distances, yes.

[saveasteading]

1 hour ago, Nickfromwales said:

Ground floor WC's do not (typically) need an AAV or a vent etc.

I wasn't aware of this.

Whatever the guidance, they do need an aav. The flush creates a vacuum and will draw air or water behind it either from a vent or from sink, bath or shower traps. Better to be air.

 

Plus the vacuum can prevent full flushing.

I've seen this myself recently and had to clear the blockage. I had temporarily closed off the svp from the existing farm wc,  thinking it will work for a while. The wc flushed poorly and a blockage followed.

Temp svp bunged in and all is OK.

I may fit a full svp as it serves a septic tank which may burp, or perhaps just an AAV.

[Nickfromwales]

1 hour ago, saveasteading said:

Whatever the guidance, they do need an aav. The flush creates a vacuum and will draw air or water behind it either from a vent or from sink, bath or shower traps. Better to be air.

 

Plus the vacuum can prevent full flushing.

Sorry to disagree, but you know I will.....

 

They do not need an AAV when the drop is <1300mm, some BCO's have stated <1100mm, but tbh most inverts for GF WC's is way less than this. Some are pretty much down and then straight out horizontally, so in all above instances these get an air-break soon enough for no such vacuum to be created.

 

Ironically, I have more trouble persuading architects who are long in the tooth, vs BCO's, that this is completely fine and functions perfectly correctly.

 

The dreaded vacuum is mostly an issue when the pellet of water etc is dropping a full 1 storey (2.4m or more) and gets up to speed, spreading out and filling the pipe as it falls. Then you defo need an AAV, but that's for falls from 1st and 2nd floors etc, only.

 

Even if the WC is discharging immediately downwards it's fine, but if you have even a slight turn to the left or right, giving a small section of horizontal pipe before it drops the <1300mm, then the issue is basically zero. The horizontal pipe creates an instant air break, and the (perceived, possible) problem instantly gets a cure.

 

BCO's have argued, then come to terms, and then they finally agree; some have then asked to see the WC functioning, before sign-off, but concede when they see it working flawlessly. Most just give up at the 1st challenge, where I say "it doesn't need one mate".

 

Saves horrible boxing-in in the corners of the rooms with the requisite access panel etc.

[saveasteading]

54 minutes ago, Nickfromwales said:

Sorry to disagree, but you know I will.....

 

You are right to of course.

I would have said the same until this happened, else I wouldn't have clipped the blank end over it.

Straight out through wall, then vertical for about 600mm, then a 90° turn along the wall. Thereafter it heads to the septic tank of which I have no knowledge other than there is a cover.

 

There may be some other cause eg the tank being full and not draining.

But as soon as I released the stopper it all flowed. Nearly all. Yeugh.