Different types of soil stacks

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I have 2 types of soil stacks in my bungalow :

The first is in my internal ensuite which runs into the attic and then vents externally through the roof.

The second is in my main bathroom and only runs to a height of 1.5m, where there is a white cap which can be unscrewed (I'm assuming this is for access to clear blockages)

Why does the second stack not vent externally ? Does the second stack need to be at this height or can I reduce the size to 1m ?

The reason for asking is I'm undertaking my second bathroom fit out and looking to box up the wall with the stack up to 1m as this will hold all the toilet, sink, and bath pipework.

Many thanks

Iain
 
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is what you should have a stub stack it has to be above flood level usually the basin ;)
 
Thanks for the prompt reply, I thought it might have somthing to do with that.

As a matter of interest why does it not join to the other stack which vents to the outside ?

Thanks
 
When i did my Document H (sanitation) module in college - I thought it was higher than the highest trap it serves (yes i know that would basically equate the spillover level of a basin but just checking the definitions).
 
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Thanks for the reply.

If it is the highest trap then this would allow me to reduce the size to 1m, as the highest trap is the bathroom sink in that room.

I wasn't sure whether it would be the height of the sink as when full this would have the greater head of pressure (just guessing here, might be the bath depending on volume)

Any other comments welcome.
 
I wasn't sure whether it would be the height of the sink as when full this would have the greater head of pressure (just guessing here, might be the bath depending on volume)

it needs to be above the rim of the basin (flood level) ;)
 
just flicked through Building regs document H and ther is little info on the use of AAV.


A stub stack has different regs as this type of system uses a completly capped end with no AAV?
 
Bstr

Correct about the end cap this is a screw cap and is not vented, does this mean the other stack would handle any flood level, and this "stub stack" is only to provide a fail safe in the event that the other stack is blocked ?

There are 2 rodding drains 1 at each of the stacks outside, this might mean there is no link between the two and that each stack is independant, therefore flooding could be possible even if the other is not blocked.

sorry becoming a long topic !
 
stub stacks have to be connected to a ventilated drain and they can only rise 2meters from the drain invert but if an aav is fitted there is no restriction on the height.

The stub stack should be no more than 2m from the drain invert (where your pipework meets the main ventilated drain) to the highest trap. If it is more than 2meters put an AAV on instead of the capped end and extend the pipe so that it is above spillover level (as the guys said and not to the highest trap as i said :oops: ).

got that?
:LOL:
 
The sub stack was installed in the house when built with a non vented cap, so I'm assuming that it must be within 2m from the ventilated drain. It is also less than 2m from the toilet, sink, and bath.

Think I understand what you are talking about.
 
Just re-read your original post and ....yes you can reduce the height of the capped end.
 
Bster, why the change of mind ? Just trying to increase my limited knowledge of plumbing.

Thanks for all your prompt help

Iain
 
highest trap?....not disputing it`s written in lawful regs But..........it must be there to cover the eventuality of a completely blocked stack/pan on a 1st floor level in most domestic situations .........overkill in my opinion.....thoughts, Guys
 

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