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Housing - New Build: Soil Stack Pipe State of the Art

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  1.  
    I've succumbed to the depths of working out the best way to fit soil stack pipes into my new Passivhaus build. In particular I'm concerned about insulation and airtightness, but also about appearance.

    I guess that airtightness is predominantly dealt with by the traps on the waste pipes, so this probably isn't a major concern. Is this correct?

    On the insulation front, it seems to me that having a large diameter pipe running from the inside of the building through to the outside is probably a bad idea thermally. I imagine that with a suitable airflow across the top of the pipe it could suck air up from the sewer and steal a lot of my precious heat from the building. I don't really want to have to insulate it/them to u=0.1... Am I being paranoid? Would the use of an air admittance valve help here?

    I think that with our floorplan we may need at least two stack pipes to service all the wet rooms. I'm not very keen on having visible stack pipes protruding through the roof of our nice clean contemporary design. What's the best way of minimising the visual impact? It looks like air admittance valves can be fitted internally, with no need to penetrate through the building fabric. Am I interpreting this correctly? If so, does it work in the real world?

    Some searching found http://markbrinkley.blogspot.com/2005/09/avoiding-drain-smells-in-bathroom.html which refers to a Hepworth product which if used appropriately can avoid the need for a soil stack at all. Anyone know if this really works or if they bring additional problems?

    Bottom line - what is the state of the art for soil stacks in a Passivhaus?
    • CommentAuthortony
    • CommentTimeJan 12th 2010
     
    you could use trendy new traps with a reed valve in them instead of durgo valves.

    good idea to think about it now -- I put mine outside round the back
  3.  
    When I think of reed valves I think of Yamahas!
    • CommentAuthorDarylP
    • CommentTimeJan 12th 2010
     
    .... RD? :smile::smile:

    AAVs work fine, in the loft or where ever is suitable. I have never had a problem with them in over 5 years.

    Cheers.....
  5.  
    .... RD?

    Yup.
    • CommentAuthortony
    • CommentTimeJan 13th 2010
     
    I have had problems with durgos blowing open in gusty winds and getting stuck in open position with smelly consequences.
    • CommentAuthorCWatters
    • CommentTimeJan 13th 2010
     
    My understanding is that the stack furthest from the main sewer has to be open (no AAV). Any others between that one and the sewer can be short stub stacks with AAV.
    • CommentAuthoraa44
    • CommentTimeJan 14th 2010
     
    I am not convinced that it does have to vent to the open air. I can't work out how to cut and paste it from the PDF into here, but section 1.33 of Approved Document H says "Ventilated Discharge Stacks may be terminated inside a building when fitted with air admittance valves..." You have to be able to get at the valves for maintenance but I don't read it as saying that external ventilation is the only way. Although I am in Scotland it is an issue that I want to get to the bottom of as our site is really exposed and I am not sure what gale force winds whistling across the top of the soil pipe would do.
    •  
      CommentAuthordjh
    • CommentTimeJan 14th 2010
     
    I just put a HepVO trap on a bath to avoid the need to cut into a joist to fit a normal trap. To soon yet to say how well it works, I'm afraid.
    •  
      CommentAuthordjh
    • CommentTimeJan 14th 2010
     
    aa44, I've seen statements that the risk with no open vent is that flushing a toilet can cause raised pressure in the stack that slows the flush and/or causes blowback through other traps.

    This BBA certificate for an AAV - http://www.ribaproductselector.com/Docs/1/21531/external/AG094650.pdf?ac= - has some specific guidance about when and where open vents should be used in addition to the valves. See p7. I guess other manufacturers will provide similar statements for their products.

    Cheers, Dave
    • CommentAuthorCWatters
    • CommentTimeJan 14th 2010 edited
     
    Posted By: aa44I am not convinced that it does have to vent to the open air.


    I was thinking of 2.18...

    "The system should be ventilated by a flow of air. A ventilating pipe should be provided at or near the head of each main drain. An open ventilating pipe (without an air admittance value) should be provided on any drain fitted with an intercepting trap... continues.."

    It's also what my BCO wanted. He had no problem with an internal AAV on the middle stack but said the one at the back (eg at the head end) he said must be open.
  12.  
    Posted By: DarylPAAVs work fine, in the loft or where ever is suitable. I have never had a problem with them in over 5 years.

    Cheers.....


    One more detail - no loft in this house. There will be a service gap between the internal ceilings and the underside of the roof, for MVHR etc. but not generally accessible.

    In this case internal terminations will need to be done inside the living areas of the house.
    • CommentAuthortony
    • CommentTimeJan 14th 2010
     
    basic design principle is design for fail safe.
  14.  
    Posted By: djhaa44, I've seen statements that the risk with no open vent is that flushing a toilet can cause raised pressure in the stack that slows the flush and/or causes blowback through other traps.


    I can see that an open vent will relieve negative pressure in the stack above the flushing toilet/emptying bath, but can't see how it would do anything to relieve positive pressure below the flushing toilet. I would have thought the opposite - that negative pressure above the descending water "plug" would slow down or break up the descent of the water helping to keep the pressure rise below the "plug" lower.
    • CommentAuthorTuna
    • CommentTimeJan 14th 2010
     
    Posted By: MarkBennett...negative pressure above the descending water "plug" would slow down...


    Would a flushing toilet cause a 'plug' in a standard 4" pipe? I would have thought it would collapse against the wall of the pipe pretty quickly, if not instantly. Positive pressure would be due to the admittance of an additional volume of 'stuff' into the pipework, rather than piston-like behaviour?
  16.  
    Is it permitted to vent a soil pipe into a ventilated tile batten cavity, i.e. below the tiles, but above the sarking membrane & a rigid sarking board?

    Is there any reason why it needs to run vertically above the WC connection? Could it slope through the roof space & connect to an air brick in the gable wall?

    David
    • CommentAuthortony
    • CommentTimeJan 14th 2010
     
    cant finish below tiles but you can use a tile vent or vent tile

    gable wall is more difficult -- usually have to terminate above roof or eves.

    they tend to ice up if tile vents are used -- steam often comes out so under tiles would lead to mould and rot and mushrooms.
  18.  
    Bumping this thread as it's been a number of years and it didn't actually seem to have a resolution.

    With our flat roof being our outside space any external soil pipe is going to be rather ugly. We also have no loft.

    The bathrooms are stacked above each other with a single soil pipe dropping through a service duct. Am I right in thinking I just need an AAV/Durgo at the top of the stack in the top bathroom with a service panel to allow access (and a grille to ensure it's not in a sealed space - probably best for this to be the bathroom rather than the adjoining bedroom) and one above the overflow level of the washbasin?

    The kitchen sink/dishwasher will be on a branch of about 4m - I thought I read somewhere it was necessary here as well but can't find the reference now.

    Finally, are HEPVO traps and alternative to the AAVs on the basins?
  19.  
    Note - comment on kitchen sink is nonsense. Will be less than 3m.
    • CommentAuthorEd Davies
    • CommentTimeJul 22nd 2014
     
    Related thread: http://www.greenbuildingforum.co.uk/newforum/comments.php?DiscussionID=11869

    I hope I can have just AAVs in the house and the vent pipe on the treatment plant. If not, maybe a stack that goes up to ceiling level in the bathroom then back down and vents under the house. If not even that then a stack to ceiling level in the bathroom then a narrower pipe up through the loft to vent through the gable wall.
  21.  
    The image in that thread suggests it's fine. Do you know the reason for the AAV on the right of it though?
    • CommentAuthorEd Davies
    • CommentTimeJul 22nd 2014
     
    Or alternatively, why there isn't one on the left? I'd have thought the bathroom 40 mm pipe would be in more need of one than the kitchen as a heavy slug of water from the basin could depressurize that run enough to suck water out of the bath's shallow trap (or v-v).
  23.  
    ref HEPVO traps - I wouldn't unless no alternative - they just need too much maintenance.
  24.  
    Yes, the problem we had in our last place was with the washing machine joining the sink trap - that seemed to be enough to 'burp' the trap as we'd get a waft of bad air sometimes. It must have refilled though as it we didn't need to run the tap to stop it smelling. I'm not sure an AAV would solve the problem there - I think it was probably teh style of appliance connection shown next to the sink in that image (and actually just drained through a hole in the wall to an external surface drain)
    • CommentAuthorTriassic
    • CommentTimeJul 22nd 2014 edited
     
    Is it necessary to for the vent to be 110mm, I was wondering if something a lot smaller would do, maybe as small as 32mm? I assume the vent is simply to stop the water seal in the trap being sucked out by the siphoning effect, so you could try increasing the size of the vent to the point this does not happen?
    • CommentAuthorEd Davies
    • CommentTimeJul 22nd 2014
     
    Posted By: TriassicI assume the vent is simply to stop the water seal in the trap being sucked out by the siphoning effect,
    Not sure. If it was only sucking (negative pressure) then AAVs would suffice I assume. Isn't there also a worry about positive pressure under some circumstances? Not clear quite what, though.

    Be good to know what as it's the sort of thing which could be tested experimentally - doesn't need a house, just some 110 mm pipe, junctions, 40 mm pipe, trap, water and long bit of whatever thinner pipe is to be tried. bit of cloth wrapped round something to make a piston in the 110 mm pipe could reproduce pulses of both positive and negative pressure.
    •  
      CommentAuthordjh
    • CommentTimeJul 22nd 2014
     
    Posted By: TriassicIs it necessary to for the vent to be 110mm, I was wondering if something a lot smaller would do, maybe as small as 32mm?

    I have half a memory of reading something about this (in English regs) and the magic number being 50 mm or possibly 75 mm or maybe I'm imagining it all.

    FWIW, our BCO had a look around a couple of weeks ago and correctly identified a short stub outside our house as being the vent pipe. I presume that since the purpose of his visit was to check our roof structure, he had also noticed that none of the internal soil stacks penetrate the roof (the roof ply skin is structural). We have NO roof penetrations at all, yeah!
    • CommentAuthorSimon Still
    • CommentTimeJul 22nd 2014 edited
     
    Posted By: Ed Davies
    Posted By: Triassic.......Isn't there also a worry about positive pressure under some circumstances? Not clear quite what, though.



    Yes - fermenting waste trapped within the house system produces gas which is forced up through your traps. Again, I'd have thought a very small vent would suffice - it's going to have to be a lot of gas to push through a trap of water if there's any opening at all. Makes me think even 50mm would be very conservative
    • CommentAuthoratomicbisf
    • CommentTimeJul 22nd 2014
     
    I've been thinking about this too as I'd like to remove the internal soil stack pipe in the bathroom in order to give a little more room. Some say it's not a problem to replace with an AAV, others that it's not permitted. The neighbours have removed theirs with no ill effects, but perhaps the systems are shared!

    I've been thinking of perhaps putting in an AAV but with an extra pipe put in an internal wall alongside the ventilation duct I was talking about in another thread as a back up. If the AAV causes problems, I could use the backup pipe.

    Ed
    • CommentAuthorleakyPipes
    • CommentTimeJul 28th 2014
     
    You need one stack open to air because of potential methane buildup

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