Septic Tank Ventilation Design

[leighduffy]

Good Evening All,

May I first start by offering my congratulations and thanks for a very informative forum and excellent research tool for all elements of plumbing; both professional and novice.
Apologies for the lengthy first post, but I wanted to be as comprehensive as possible to gather information from the experts!

I am having some trouble designing the ventilation of my sanitary/soil system to best work with my newly installed foul waster septic tank/soakaway system on a new-build. To try to clarify the issue I have sketched my current setup, with installed foul drainage pipework in blue, along with details of appliances in each bathroom/kitchen, and additional options for septic tank ventilation in red:
https://www.dropbox.com/s/ic8j1qekg3bi8ex/Septic Tank Ventilation Plan.jpg
My plumber has limited experience with plumbing to a septic tank system; he has used Air Admittance Valves int the majority of his past jobs (onto mains sewer) with no issues but obviously this will not be acceptable in my case. I have a couple of queries as to how we can optimise our installation and I hoped somebody here with past experience / better knowledge of Part H of the Regs may be able to offer some pointers, or raise any issues for discussion.

Here are my thoughts:

• Ventilation in the house to be provided by soil vent pipes into loft/roof from Upstairs WC and and Ensuite to ventilate heads of both long drain runs to Septic Tank. (Kitchen waste to be unvented due to smaller appliances draining to this run.) Can we get away with AAVs here or are open Vents better suited, given the lengths of drain runs from the Septic Tank?
• If Vents are required, can somebody advise if it woud be acceptable to bring SVP into loft space vertically, onto a 90deg elbow and terminate to a grill such as this through wall horizontally, as a more asethetic option? Would this not conform to Regs or affect performance of the vent?
• The Septic Tank is fitted with an Inlet and Outlet Tee, both of which have capacity to vent. The Tank cover/frame has an opening to take one vent to just under the cover, alongside the main inspection neck. I had initially planned to vent the outlet vent through the cover as I had assumed there would be less smell as this 'side' of the tank is clarified water, whilst the inlet side will be where most biological activity will occur.
• I had finally planned to run the Inlet vent horizontally to bottom of garden where a vent stack could be concealed and vent to a safe height without looking unsightly and whilst evacuating any smells a fair distance from seating areas. Would this be effective? Would it be better to vent to a closer location such as the wall in close proximity to the tank? In this case could we get away with an AAV to eliminate smells? I believe this vent will primarily function as an air inlet rather than pressure relief, but if somebody could confirm which of these four possible vent points will likely experience positive pressure, negative pressure or a combination that would be very helpful.

Sorry to throw all of this information at you guys, just tried to empty all options the options out of my head! Hopefully the diagram will clear things up and I really would appreciate hearing if anyone had an opinion of what would be the best option here, particularly if it is an option that has not been considered!

Many Thanks in Advance,

Cheers,

Leigh.

 

[erpkid]

Welcome to the forum.

 

[leighduffy]

Many thanks erpkid.

 

[erpkid]

Sorry I know nothing about this sort of stuff. I am sure someone will be along who does though.

 

[lame plumber]

best thing you could do is run the whole lot past buildings control/environment agency officer both of whom seem to take an interest in septic tanks now that the rules have become very much more controlled. they will give you the heads up and what to do. be very careful not to carry out works that may fail later on as the environment agency can and will make you make good any faults down the line, unlike building control who only have a year to catch you out. only reason i know is that i was looking to buy a house and put in a micro sewage plant next to a stream, many many hoops to jump! sale fell through tho:cuss:

just looked at your drawing for septic tank, not as much hassle as sewage plants or holdingtanks (forgotten name of system!!) chat to buildings control, looks ok from here tho, only issue is horizontal vents out of loft wont meet regs as soil vents have to clear gutterline.windows etc

 

[Mike Jackson]

A horizontal vent will be fine as long as it is 1m above and 3m horizontally away from any opening.

 

[leighduffy]

Many thanks all for the helpful responses, apologies for the delay in response.
Mike that solution would certainly be the most aesthetic although I wonder how effective it would be, lacking the 'draw' that a traditional soil vent pipe would have. Do you have any thoughts or experience on how well this design would work?
Having spoken with Klargester Technical I am contemplating another solution that they felt would be acceptable: fitting Air Admittance Valves fitted within the loft space with both Septic Tank inlet and outlet chambers vented independently to atmosphere. This is more convenient in my case and Klargester felt sufficient to exhaust any sewer gases whilst the AAVs would prevent syphoning whilst flushing. Would welcome any thoughts on this approach?
I haven't yet had Building Control's thoughts on this suggestion but notice that my neighbour who installed his Septic Tank two years ago doesn't appear to have any Soil Vent Pipes so assumed that my local Building Control must be open to other solutions.
Look forward to hearing your thoughts,
Leigh

 

[Reg Man]

I am a bit old school, but I recollect, that it was normal practice to have aleast one open vent when using ARV's. so in this case two open vents where indicated on the drawing. To be vented externally above and away from any openings into the building, so normally above the gutter line because of your roof space ventilation grilles. Check it out with the building control officer, he may give some tolerance on this. Refer Part H section 1.32. on page 11.

 

[chris watkins]

Good Evening All,


My plumber has limited experience with plumbing to a septic tank system; he has used Air Admittance Valves int the majority of his past jobs (onto mains sewer) with no issues but obviously this will not be acceptable in my case.
I know it is likely to a bit late now but your plumber should know most of this & if they didn't you could have employed a consultant. (cheaper to ask here, I suppose)

• Ventilation in the house to be provided by soil vent pipes into loft/roof from Upstairs WC and and Ensuite to ventilate heads of both long drain runs to Septic Tank. (Kitchen waste to be unvented due to smaller appliances draining to this run.) Can we get away with AAVs here or are open Vents better suited, given the lengths of drain runs from the Septic Tank? No vents or AAV's would be required for these short runs
• If Vents are required, can somebody advise if it would be acceptable to bring SVP into loft space vertically, onto a 90deg elbow and terminate to a grill such as this through wall horizontally, as a more asethetic option? Would this not conform to Regs or affect performance of the vent? The head (end) of a drain run should always be vented (Part H) it would be wise / good practice in this case to make the two longest runs SVP's. Yes they can be joined together in the loft & taken out through a gabled end or into a vent slate so long as it provides a similar cross sectional area as the vent pipe it must also meet the requirement of discharging close to windows or vents into the building. It should also be positioned to avoid pressures from the prevailing wind effecting the trap seals through wavering out.
• The Septic Tank is fitted with an Inlet and Outlet Tee, both of which have capacity to vent. The Tank cover/frame has an opening to take one vent to just under the cover, alongside the main inspection neck. I had initially planned to vent the outlet vent through the cover as I had assumed there would be less smell as this 'side' of the tank is clarified water, whilst the inlet side will be where most biological activity will occur. Why not check the manufacturers instructions regarding venting requirements, from what I know of these units (& that isn't a lot) the in & out connections have branches fitted to allow access for inspection & not necessary for venting, the one under the main access lid will probably require venting, depending on the design.
• I had finally planned to run the Inlet vent horizontally to bottom of garden where a vent stack could be concealed and vent to a safe height without looking unsightly and whilst evacuating any smells a fair distance from seating areas. Would this be effective? Would it be better to vent to a closer location such as the wall in close proximity to the tank? In this case could we get away with an AAV to eliminate smells? I believe this vent will primarily function as an air inlet rather than pressure relief, but if somebody could confirm which of these four possible vent points will likely experience positive pressure, negative pressure or a combination that would be very helpful. Can't see a problem in running up the garden so long as the vent pipe terminates correctly, does not effect anyone next door, it should be accessible for checking & clearing, it should have a fall continually back to the tank. An AAAV (durgo) can not be used as these only allow air in & not out as required to vent the gases.

Leigh.

Answeers in Bold, How that helps Leigh ? bill is in the post LOL

 

[leighduffy]

Thanks for the input again Guys.
Will run it past BC and report back once I have confirmation - will be interesting to see towards which approach they sway!
Chris, I'd be particularly interested to look further into your Vent Tile suggestion. This would be convenient for us as I currently have 2 Vent Tiles installed for Bathroom Ventilation which I could 'tap into' with a Tee, having the SVP as one outlet and the Fan Ducting as the other. I'd be interested to hear anyone's thoughts on this before we consult BC as this would provide us a seemingly ideal, non-intrusive solution!
Cheers, Leigh

 

[chris watkins]

Thanks for the input again Guys.
Chris, I'd be particularly interested to look further into your Vent Tile suggestion. This would be convenient for us as I currently have 2 Vent Tiles installed for Bathroom Ventilation which I could 'tap into' with a Tee, having the SVP as one outlet and the Fan Ducting as the other. I'd be interested to hear anyone's thoughts on this before we consult BC as this would provide us a seemingly ideal, non-intrusive solution!
Cheers, Leigh

Hi Leigh
Don't understand exactly what you are proposing, you will not be allowed to Tee into the extract system, if you do use a slate it will have to be dedicated for is & be located so that it is a minimum of 900mm above any openings (or other vents) in or out of the building. The connection between the 110mm vent pipe & flexible pipe on the vent slate will have to be correctly made.

 

[Reg Man]

Thanks for the input again Guys.
Will run it past BC and report back once I have confirmation - will be interesting to see towards which approach they sway!
Chris, I'd be particularly interested to look further into your Vent Tile suggestion. This would be convenient for us as I currently have 2 Vent Tiles installed for Bathroom Ventilation which I could 'tap into' with a Tee, having the SVP as one outlet and the Fan Ducting as the other. I'd be interested to hear anyone's thoughts on this before we consult BC as this would provide us a seemingly ideal, non-intrusive solution!
Cheers, Leigh

With Chris on this: Slight misunderstanding, you can not vent the stack into an extraction system. The open vent stack must remain seperate. Just have to fit an addional ridge vent and connect to that.

 

[leighduffy]

Thanks Chris and Reg Man for clarification.
I thought it unlikely but queried as it would have proven convenient, with each bathroom requiring a SVP having an installed ducting system with adjacent vent tile.
Would it be acceptable to common up each extractor ducting in the loft and vent to one vent tile, then common both SVPs and vent to the other, thus keeping them independent? This would remove the need to access, disturb the roof tiles altogether, but can you see any drawbacks with such an arrangement?
Thanks for your input guys,
Cheers,
Leigh

 

[Reg Man]

I would not link the two up if they have mechanical extraction could cause venting problems. Don't see any problem if they are passive ventilation ducts. Have you considered a vented tile to match your existing tiles rather than a ridge vent; this would be easier to install as it should just replace a tile rather than involving cement work.

 

[leighduffy]

Sorry Reg Man, I might not have made things clear, it is Vent Tiles, as opposed to the ridge vent, that I currently have installed (2x), connected one to each extractor fan outlet . What I was querying was whether I could remove a ducting from one vent tile and common with the other ducting, then use the 'spare' vent tile to vent the two Soil Vent Pipes, again commoned up. Would involve piping one SVP from one side of house to other in loft though - do you think this would affect the effectiveness of the ventilation / draft?
You are right, two additonal vent tiles would be an ideal solution, I'm just looking to explore alternative options as getting back on the roof without scaffolding will be a bit tricky and I was hoping to avoid disturbing the roof if possible!
Thanks for your continued advice which is most appreciated!

 

[chris watkins]

As I have said before, I thing, the two vent pipes can be connected together (& could be reduced to 3" / 82mm) so only requiring one vent slate.

 

[leighduffy]

Thanks Chris, Reg Man.
That sounds ideal then - if I can common up each SVP through one vent tile without adversely affecting the draw of the vent then that is what I will do. Many thanks for your persistent input with this.
I'll be sure to report back my BCO feedback when he next visits, in the hope it may clarify for others in my position in future.
Regards,
Leigh.