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Venting a soil stack

Discussion in 'Plumbing and Central Heating' started by Milleniumaire, 5 May 2021.

  1. Milleniumaire

    Milleniumaire

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    Recently had a nightmare with a blocked soil stack at my elderly in-laws. It took a company 6 hours over two visits to unblock the stack and they have identified some breakage of the soil pipe bend at the bottom of the stack, which will need to be repaired/replaced and as it is an internal stack it looks like it will be costly! Fortunately, the soil stack ran through the roof and so was vented to the outside, which allowed access to unblock it.

    That got me thinking about our soil stacks! At one end of the house is the house bathroom with an external stack, vented externally. Not a problem. At the other end of the house is the en-suite with an internally boxed stack and nothing to be seen on the roof, so I assume it is internally capped (with an AAV?). The house is 22 years old. Frequently, over many years, we do get strong smells in the en-suite and I guess this is due to the soil stack being vented into the roof space, rather than externally.

    I'm now wondering if we should do something about this, but what are the options?
     
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  3. Hugh Jaleak

    Hugh Jaleak

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    As long as you've one vent on the system, it's not an issue to have AAV's on other stacks. Not unknown for AAV's to stick open, which could be the cause of the odours. I'd locate it, and see what type you have, (and indeed if it's the push fit type, it's still located in the pipe!), and then look at repair/replacement as required.

    Have the In Laws had a CCTV survey done to ascertain the situation. If pipework is still fairly complete then possible a 'Patch' can be inserted remotely and cured to provide a structural lining inside the pipe, negating the need to excavate and repair.
     
  4. Milleniumaire

    Milleniumaire

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    Unfortunately, that isn't as easy as it sounds. The en-suite & bedroom are above the garage and have a roof directly above them, unlike the rest of the house that has a loft space. As such, there is no way to get into the roof space above the en-suite, without ripping the ceiling out or possibly removing the tiles and covering to get in from above. I guess one of the advantages of having an external vent is that it is possible to easily access the pipe from above, even though the stack may be fitted internal.

    Yes, the company used CCTV. They did suggest it may be possible to patch, but also that the damage may be too severe. We are waiting for quotes, which are likely to show a couple of options; patching or replacing.
     
  5. Hugh Jaleak

    Hugh Jaleak

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    Does the stack continue up into the roofspace? If you're experiencing odours in the Bathroom the stack may finish in the room, and a grille put somewhere to ventilate the boxwork containing the pipe. If it terminated in the roofspace, I'd expect the neutral through draft in the roofspace to disperse anything untoward.
     
  6. Milleniumaire

    Milleniumaire

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    That's a good question Hugh and the answer is that I'm not sure! The stack is boxed in in the corner of the bathroom and the boxing goes all the way up the wall to the sloped ceiling. It's difficult to say where the pipe stops without actually breaking into the box, but maybe I will need to do this.

    I agree that if the stack is capped in the box then a grill through the outside wall might help although this would be quite tricky to install as the pipe would be in the way to drill outwards, from the inside, and if drilling from the outside there's a chance of damaging the pipe when it breaks through to the inside!
     
  7. Milleniumaire

    Milleniumaire

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    Coincidentally, just received a quote from the company to fix the collapsed drain at my in-laws:

    Following our recent visit we recommend the following works-
    1. Excavate to repair the collapsing drain showed on the attached site photo.
    2. Reline/patch liner the pipe which is under the building.
    3. Add a manhole for future access, currently no access.
    4. Reline works downstream of newly installed manhole, up to 6 metres, if further works are required additional recommendation
    may be made.
    All areas will be fully reinstated.

    £2,388 incl VAT.
     
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  9. Hugh Jaleak

    Hugh Jaleak

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    Normal practice is to fit a grille in the boxing somewhere to allow the void to breathe from the room. (This would be done at time of build, if the AAV is working as it should be it will only draw air in to the drainage system, not emit odours out.)
     
  10. Milleniumaire

    Milleniumaire

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    It has occurred to me that although the boxing runs up the wall to the roof, if the stack stops half way, for example, then cutting into the boxing and possibly the external wall above the stack wouldn't be too difficult!
     
  11. Hugh Jaleak

    Hugh Jaleak

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    AAV should be above the flood level of the highest appliance, (usually the basin). Rare to see them taken up further than needed. Although it is quite possible they've terminated in the roofspace and simply left the stack open....
     
  12. Milleniumaire

    Milleniumaire

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    Having looked again, the boxed in stack is at the lowest corner of the room with external walls on both sides and the roof sloping down. So, I've realised at this point, unlike the rest of the ensuite, there probably isn't a roof void, which makes me think that the stack will end within the boxing. The height at this point is probably half the height of the full height of the room.

    I have one of those cheap Bluetooth inspection torches so could probably drill a small hole in the boxing to see what is going on and then fill it in afterwards. I'm getting grief from the missus as she thinks I'm wasting time on an issue that doesn't exist and I guess she has a point, at least while there are no bad odours!

    It seems strange there are no rodding points anywhere near the base of the soil stack. I thought there would have been rules about these types of things.
     
  13. Hugh Jaleak

    Hugh Jaleak

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    No requirement for a rodding point at the base of a stack, any reputable builder will ensure the drain is accessible from a chamber, so any clearance work can be done from there. It's rare for the vertical section to block, usually the issue is in the drain run, so takes a brave person to open an access cap at the base of a stack!
     
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