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    • CommentAuthorJulian
    • CommentTimeJul 1st 2008
    I'm told by the building inspector (approved inspector) that soil stacks still have to be vented externally. With the advent of durgo type air admittance valves is this out of date? Why can't a durgo type air admittance valve placed in a well ventilated roof void (right near a nice big soffit vent) do the job properly but without penetrating the roof covering?
    • CommentAuthorMike George
    • CommentTimeJul 1st 2008 edited
    Hi Julian. Not going to stick my neck out on this one but here is Part H. http://www.planningportal.gov.uk/uploads/br/BR_PDF_ADH_2002.pdf Page 10 seems to suggest that stub stacks are okay in some situations. I have been certainly been allowed by Building Control to fit durgos in en-suite bathrooms but it is always possible that they were relaxing the requirement - but I don't see anything in the doc which says that every stack must be vented to the outside. I would ask him [nicely] which paragraph of Partg H he is enforcing.
    • CommentAuthorJulian
    • CommentTimeJul 1st 2008
    Hallo Mike. Thanks for that - it seems fairly clear that it has been accepted that an a.a.v will perform just as well so I shall go and ask him!
    • CommentAuthorCWatters
    • CommentTimeJul 2nd 2008 edited
    AAV are one way devices. I thought stacks were to let sever gas out as well as in.

    The normal rule seems to be that your furthest stack from the main must be open but nearer stacks can have AAV.
    • CommentAuthorcaliwag
    • CommentTimeJul 2nd 2008
    Durgos and similar, ofcourse, won't last for ever...poss 20 years. Took me a week or two, in a town house with a shared stack, to work out where the smell was coming from...only when I put 2 and 2 together ie the smell occured for a period after next door flushed, that I guessed that there might be a valve in the boxing. Of course there was no vent coming out of the roof!
    Incidentally, as a temp measure a plastic bag taped to the stack works perfectly well...I kid you not
    "The normal rule seems to be that your furthest stack from the main must be open but nearer stacks can have AAV. "

    Cwatters has got it right according to my NVQ2-3 plumbing/heating book,I was looking at it the other day regarding a similiar question
    • CommentAuthortony
    • CommentTimeJul 2nd 2008
    I would add that there should be a vent pipe at the head of the main drain run and on the first one up the run too.

    The problem with valved systems is that the valves can cease to function and if a main drain becomes blacked everyone gets glugging and smells.
    • CommentAuthorMike George
    • CommentTimeJul 2nd 2008 edited
    Posted By: tony
    if a main drain becomes blacked everyone gets glugging and smells.

    more likely brown than black:bigsmile:
    • CommentAuthorchuckey
    • CommentTimeJul 2nd 2008
    An air admittance valve allows air in, i.e a loo is flushed the running water puts a vacuum on the system, the aav opens instead of a trap being sucked out or gurgling. If a aav is placed downstream of this travelling torrent, the system would be pressurised with the hypothetical possibility of a shallow trap being blown back into a shower followed by guess what! Years ago external vents were used with their little mica windows. Proper open stacks also mitigate against any decaying matter sticking in the pipes and generating gasses that will linger.
    • CommentAuthormhairig
    • CommentTimeJul 28th 2008
    I am working on a house with a private septic tank (unvented) in Scotland & was planning to vent the soil pipe at the head of the run only and use AAV's else where (2 other vertical stacks in the same building) to minimise the number of penetrations in the roof (there are lots of rooflights and don't want lots of separate stacks sticking up thro' the roof) :smile:

    The pipe at the head of the run only has a gnd. fl wc/sink/bath on it and the next one down the run has an upstairs wc/sink/shower and a wm downstairs - will this be ok?
    Does the Soil vent pipe need to terminate higher than the highest appliance in the whole house system (i.e. somewhere above the first floor) or just the highest appliance connected to it?
    Does anyone know about venting the soil pipe horizontally through a gable wall (say at first floor level so well away from the ground/people) or does it have to go all the way up and vent above the roof line somewhere? (I am aware of the 900mm higher than the top of any opening within 3m, which in my case would put the top of it 900mm above the ridge line...)
    • CommentAuthorCWatters
    • CommentTimeJul 28th 2008 edited
    I can't find anything in Part H (England) about the height of a stack except for the 900mm above an opening issue. What opening do you have on the ridge? I don't think they count ridge tile vents used to ventilate the void between roof insulation and tiles - only vents into the house.

    Sounds like one to discuss with your BCO.
    • CommentAuthormhairig
    • CommentTimeJul 28th 2008
    Hi, I have a velux rooflight either side of the ridge as high up the roof as they will go as there are bedrooms in the roof-space. The actual roof build up has no ventilation within it as we have a tyvek BM and there is ventilation above the insulation under the rainscreen cladding (there is timber rainscreen cladding on both the roof and the walls) so using something like a tile vent is out as we have no tiles!! :wink: sadly BC up here (highlands) are down to 2 consultants who cover a vast geographical area (1 in the office doing ALL paperwork, 1 doing ALL site visits) so they are swamped! Getting even a relatively quick answer is not an option!... I would really like to terminate the SVP horizontally out of the gable but the only terminals I can find are clearly for a) tiled roofs, or b) vertical termination :cry:
    • CommentAuthorCWatters
    • CommentTimeJul 28th 2008 edited
    Bear in mind that the vent doesn't have to be 110mm in diameter. I believe 75mm is ok, possibly even 50mm. Check the regs. That might open up more options for the terminal. What about the terminal used to ventilate flat roofs? Perhaps not these exactly but..


    A 50mm pipe is approx 2000 sqmm
    A 70mm pipe is approx 3850 sqmm

    so these appear to have roughly the right free area.

    Edit: Now that I think about it.. I'm not quite sure why you couldn't just cut pipe flush with the wall and fit one of these..
    or if your really want fancy how about a nice brass terminal...

    I suspect the BCO might react better to something industrial looking. Perhaps replace it when he's gone :-)
    • CommentAuthormhairig
    • CommentTimeJul 28th 2008
    Yeah, I did think about something like the option you show from www.aquafax.co.uk as that is what is happening with the ventilation duct from the bathrm & utility extracts - we were going to put these


    on the end of the duct behind the open rainscreen cladding as it is a well ventilated space and that means they are concealed from view externally...

    I wasn't sure if something different was actually required for svp's or whether it's just a matter of previous convention! (i.e. most houses don't have rainscreen cladding on the roof!) Prob. should try and check with BC first so we can press on with the cladding but hopefully that will be fine! Thanks for the advice! :smile:
    • CommentAuthorJohan
    • CommentTimeJul 29th 2008
    I get the impression from paragraph 1.32 in Part H that having a AAV is ok as long as you have some form of other open air ventilation for the under ground drainage. Or have I missunderstood?
    • CommentAuthormhairig
    • CommentTimeJul 29th 2008
    that is the English regs but yes, I think you are correct. Only problem with that for us is the unvented septic tank means that at least one stack needs to provide the ventilation and there are a lot of rooflights so the svp will need to project quite high above the roof line - not pretty!
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