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Building Regulations and Standards: SVPs v AAVs

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  1.  
    • CommentAuthorEd Davies
    • CommentTimeMar 15th 2014
     
    East-west A-frame house, single story + loft. http://edavies.me.uk/2014/02/sketch-update/ Bathroom and kitchen adjacent near the middle of the south side (windows 2 and 3 in the picture counting from the nearest as 1) on the ground floor. Putting a soil vent pipe up the outside of the building would in theory be possible but would look odd and be a bit of pain so my house designer has sensibly specified “S.W.V.P. to be taken to roof vent terminals”. Sewage goes to a treatment plant a few metres away.

    Still, that's an additional bit of complication at ridge height and something of a cold bridge. Can I just have an internal SVP up into the loft above the bathroom and kitchen with an AAV there?

    Scottish Building Regs seem to say, yes: http://www.scotland.gov.uk/resource/buildingstandards/2013Domestic/chunks/ch04s08.html#d5e8221
    • CommentAuthorCWatters
    • CommentTimeMar 15th 2014
     
    If you are allowed to have one in a warm loft (to avoid the thermal bridge) then I don't see why it needs to be in the loft and not lower. For example AAV must normally be >0.9m above the WC pan/washbasin. I believe this is so that in the event of a blocked pipe you can see the water level rising in the pan/basin before it gets as high as the AAV.
    • CommentAuthorMackers
    • CommentTimeMar 15th 2014
     
    Why do we use SVP instead of aav all the time? Surely the less penetrations through the thermal envelope the better?
    • CommentAuthorEd Davies
    • CommentTimeMar 15th 2014
     
    CWatters: thanks, that's a good point. Much better to have the AAV in the bathroom (near ceiling level) where any problems can be seen, are easier to clean up and it can all be ventilated better. Also one fewer penetrations into the loft - not a big deal as it'll be a warm loft anyway.

    Mackers: I think most SVPs are external and double up as the actual soil pipe from upstairs bathrooms so the lack of moving parts probably swings things in their favour. Also tradition, perhaps. But yes, on a new design you'd probably want to keep the whole stack internal and use an AAV even on a two storey house, wouldn't you?
    • CommentAuthoratomicbisf
    • CommentTimeMar 15th 2014
     
    I've always been told that one needed at least open vent in the system to allow any gases to escape. I'm in a similar boat as we have an internal stack and wanted to remove the vent part and replace it with an AAV to make the layout of the very small bathroom easier until told this.

    Certainly looks a lot better than having it on the outside of the house.

    Ed
    • CommentAuthorJonti
    • CommentTimeMar 16th 2014
     
    Posted By: atomicbisfI've always been told that one needed at least open vent in the system to allow any gases to escape.
    Ed


    Scottish building regs allow for just an internal AAV so obviously they feel it is not an issue. I have this arrangement and have had no issues.

    Jonti
  7.  
    I have one outside vent adjacent to the sewage treatment plant. There is one 110mm AAV on the main stack in the bathroom and two 50mm AAVs on the ends of the shower and basins waste pipes. The AAVs are 1100mm above first floor level. This is in England though.
    • CommentAuthorCWatters
    • CommentTimeMar 16th 2014
     
    I'm in England. I was told the BCO normally require one open stack at the furthest end from the main sewer. Any stacks on the run between that one and the main can have an AAV.
  9.  
    Hi,
    I installed above some 8 years ago (I read the specs and worked out what to do). i.e. an open stack in an en suite bathroom(the furthest from the main) and an air admittance valve in the main bathroom - this was above the level of the pan probably 1.2 m boxed in with a small shelf on top. It passed Building Control - but I don,t think the BC inspection was carried out very well.

    Richard
    • CommentAuthorEd Davies
    • CommentTimeMar 16th 2014
     
    Posted By: JontiI have this arrangement and have had no issues.
    Useful to know, thanks.

    Posted By: PeterStarckI have one outside vent adjacent to the sewage treatment plant.
    Interesting, how high is that stack - just above ground or a lot taller?

    Posted By: CWattersI was told the BCO normally require one open stack at the furthest end from the main sewer.
    Makes sense but wonder if it's different if it's going to a treatment plant which is itself vented.
    • CommentAuthorEd Davies
    • CommentTimeMar 16th 2014
     
    Posted By: HalcyonRichardi.e. an open stack in an en suite bathroom
    Sorry, assuming you don't mean an open stack literally in an en suite, do you mean an open stack up the wall outside or one going up from the en suite to the loft? If to the loft, then what - ridge vent?
  12.  
    Hi Ed,
    It goes out through the roof. I can see what you mean when I re read my post :shamed:

    Richard
  13.  
    Ed, the stack next to the sewage treatment plant is about 600mm tall.
  14.  
    CWatters, looking at the latest Part H I don't understand why the BCO would say that, unless possibly the pipe runs are very long.
    • CommentAuthorborpin
    • CommentTimeMar 16th 2014
     
    In Scotland as well. There is a bit of interpretation here. My BCO insisted on a SVP on the longest run as he said it was too far from the main drain (10M max). I have a second branch that is drawn as a SVP but I am going to fit an AAV and argue that it is sufficient.

    Last house I had a 30M run from the disconnecting Manhole and only ever had a AAV with no problems.
    • CommentAuthorJonti
    • CommentTimeMar 16th 2014
     
    borpin,

    mine goes to a septic tank and has a good run of maybe 45m though only 20ish from last manhole. BCO passed it with just AAV without any hesitation.

    Jonti
    •  
      CommentAuthordjh
    • CommentTimeMar 16th 2014
     
    I think the open ventilation stack is required to relieve positive pressures in the below-ground ventilation system. Part H clause 1.33 has weasel words that require an SVP if the AAV(s) "adversely affect the amount of ventilation necessary for the below ground system". I think I've seen somewhere that that is taken as every tenth house on an estate or somesuch, and one-off houses get one-off decisions.

    The Scottish regs refer to a BS EN. Does that say anything about the subject?
    • CommentAuthorborpin
    • CommentTimeMar 17th 2014
     
    Posted By: Jontimine goes to a septic tank and has a good run of maybe 45m though only 20ish from last manhole. BCO passed it with just AAV without any hesitation.
    As I say interpretation by the BCO at the time and if that is what he wants then that is what you have to do :neutral:
    • CommentAuthorEd Davies
    • CommentTimeMar 17th 2014
     
    Don't know about the BS EN - it's €66 which is not exactly disastrous in itself but there are quiet a few referenced in different parts of the regs and you could finish up spending a lot of money. Also there's a matter of principal involved - you shouldn't have to pay to find out what the law is. Could look in the library, I suppose.

    It seems that AAVs alone would probably be alright but an SVP could be required either physically because to get rid of any overpressure in the pipe to the treatment plant or just because the BCO thinks it's a good idea.

    So if an SVP is required, does it have to be a full 110 mm or whatever pipe nearly vertically above the highest drain point or could be a much thinner pipe (50 mm or so, perhaps) running horizontally under the house then up through the attached porch/greenhouse?
    • CommentAuthorEd Davies
    • CommentTimeMar 18th 2014
     
    PS, just got planning permission. Pretty pleased: 6½ weeks after submission and more than a fortnight before their target date.

    http://wam.highland.gov.uk/wam/applicationDetails.do?activeTab=summary&keyVal=N09ALOIH7R000
  21.  
    Well done Ed!
    • CommentAuthorJonti
    • CommentTimeMar 18th 2014
     
    Yes, well done:boogie:
    •  
      CommentAuthorSteamyTea
    • CommentTimeMar 18th 2014
     
    When does the shovelling start?
    I have a time-lapse camera, brilliant fun.
    • CommentAuthorEd Davies
    • CommentTimeMar 18th 2014
     
    Thanks chaps. Still need to get the building warrant stuff together so it'll be a while before the actual house can start but should be able to start on the entrance track and so on pretty soon.

    Not sure I can be bothered with a time-lapse camera but my expectation is to cycle through 2 days on site and one day ordering stuff/asking questions on here/domestic stuff/resting modulated by weather, deliveries and so on. Will try and blog on the “off” days with as many photos as are practical. Might be nice to do photographs from a consistent position at regular intervals, though.
    •  
      CommentAuthordjh
    • CommentTimeMar 20th 2014
     
    Posted By: Ed Daviesmy expectation is to cycle through 2 days on site and one day ordering stuff/asking questions on here/domestic stuff/resting modulated by weather, deliveries and so on

    That sounds like a good plan. There aren't enough hours in a day!

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