Soil stack venting - building regs ...?

Hi All Wonder if anybody out there is familiar with the building regs requirements re venting of soil pipes ?
I'm trying to get a completion certificate from our local council's Building Control bods. One of their queries concerns the drains...
We have two drainpipes from our bungalow - both of which end up in our own septic tank. The main run connects to two WCs, 2 baths and various sinks. It looks as if this was, at one time, vented through the roof via a 4" pipe from inside the bathroom. This pipe has been removed, and an a air-admitance valve has been fitted at floor level.
The other drain runs under the floor of the garage, and only carries waste from the washing machine and a single stainless kitchen sink. These waste pipes enter the drain via a short 4" stack with aav - inside the garage.
The Building Control chappie has queried the second drain (he doesn't know about the original one) - and would like to see it vented to outside - requiring that the vent be 900mm above any opening window - or more than 3m away from any opening window.
Because of the way the bungalow is laid out - this will look pretty awful - but is do-able.
So - a couple of possible solutions - I'm wondering which of them meet the Requirements....
Option 1 - Vent the second soil stack in 4" pipe through the back wall of the garage and up the gable end of the new extension to the bungalow - won't look very pretty.....<g>
Option 2 - As (1) - but run the 4" pipe back along the rear of the garage flat roof so it ends up more than 3m from opening windows and terminate the vent at garage roof level
Option 3 - Leave the venting as is in the garage - but reintroduce a vertical vent pipe in the bathroom. Could this terminate in the loft space with an AAV - or must this go through the roof ? Also - does the air vent need to be 4" - or can it be in a smaller pipe (like basin / bath waste pipe ?) - as this would be much easier to accomodate in the bathroom.
Before anybody says 'ask the Building Control people' - they're desperately short-staffed at the moment and catching up wth somebody to answer questions is a heck of a job - and I'm hoping that somebody here might have been round this one before...
Thanks Adrian - Suffolk UK ======return email munged================take out the papers and the trash to reply
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I believe you can vent a stack with an AAV in the loft, but not in a habitable room (don't know about a garage). The stack can be reduced in size for the portion which forms only the vent, but this is so rarely done you might have to find the relevant regs to point it out to the BCO. I found it for a friend having an extension built, but their BCO had never seen it before.
--
Andrew Gabriel

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Hi Andrew
Thanks for the comments - see below .....
On 27 Sep 2005 22:27:07 GMT, snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) wrote:

My 'gut reaction' says that a garage isn't a 'habitable room' - but that's only common sense - noting to do with Building Control <g>

Yes - I had an extensive Google yesterday and the 'dry' part of the vent (above the highest basin overflow) can be reduced to 3". This would help a bit - but I'm still going to have to do a fair bit of bulky boxing in in the alcove where the basin is fitted - bother !
I believe I read it that the top end of the stack can be in the loft, with an AAV fitted - but I'll double-check.....
I guess I'd better come clean with the BCO about the odd arrangements in the bathroom, and get him to approve the changes there at the same time as agreeing what's to be done in the garage - rather than do part of it and then have them fail the job on the other part.
To make it more exciting <g> - they're also insisting that part of the underside of the garage roof, where the garage adjoins a recent extension to the house, is skinned in Supalux or Masterboard - but only for a section of the roof (width as yet unspecified). The alternative to this is replacing 12ft x 4 ft of double-glazing with wired or fire-resistant glass - somehow I think that's going to be the more expensive option !
Wish I'd got the Building Cert 4 years ago while I was still doing the work !
Thanks for your comments - much appreciated Adrian ======return email munged================take out the papers and the trash to reply
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