Soil pipe venting question

[reds42]

Hi,

Im looking to convert a ground floor understair cupoard into a toilet. However I'm not 100% sure whether I'd need to fit an air admitance valve on the pipework by the new toilet.

My rough diagram shows the basic layout Im looking at.

Drain

• reds42
• 14 Mar 2017

The outside inspection chamber is already there and has a spare inlet I plan to connect to.

New pipe run is approximatley 6.5m long from the propossed toilet to the inspection chamber.

Fall on new pipe run will be a little better than the minimum required at about 25-30mm per meter even along its length.

A hand basin waste will be connected into the new run by the toilet.

Now having had a look at Part H I'm a little unsure on the requirement for venting this pipe run. Table 2 says upto 15m unventilated is acceptable, and diagram 3 is giving a maximum of 6m for a single WC on a branch to a stack.

My assumption is that as Im not connecting to the stack I go with table 2 meaning I dont need to vent the new run, so would not require and air admitance valve in my arrangement. Would this be correct?

I am aware this is notifiable work and I've dealt with building control before.

Any input much appreciated.

 

[dilalio]

Building control's requirement trumps all!
Give them a call, my experience with them is that they're generally there to help you with things you're unsure of.

 

[rules&rulers]

Quick reply,the clue is that you are not connecting to a stack/branch.
Think about rodding access points thou,i am sure you have.

good luck.

 

[Hugh Jaleak]

An AAV isn't mandatory, but it wont hurt in that instance, I'm more concerned about the number of bends you need to achieve that run! Think you may have to go back to the drawing board there, BCO may not allow your proposed run without adequate rodding access being provided.

I'd think about using a chamber to turn the new drain as required where it exits the property, and come into the existing chamber at the 12 o'clock connection, picking the existing stack up on a junction as you pass it. You've got two sharp turns on that proposal, using bends underground is asking for trouble.

 

[reds42]

Thanks for the input all.

I agree the use of bends is not ideal, but my diagram is missing some details. I was planning on using a long radius bend where it leaves the house. Did consider an access chamber but thought I would get smoother flow with a long bend. Id be adding rodding access to the run under the house floor, and also the angle of the connection to existing chamber is not quite as bad as the diagram would lead you to believe. Did think about intercepting the run from the stack but thought adding a junction away from manhole could make rodding difficult.

I should of spent more time making a clearer more accurate diagram - lesson learnt!

I was hoping not to have to install an AAV as they are prone to fail sealing with age resulting in a stinky room. If I don't have to fit one its one less thing to go wrong and have to fix later.

Think there will be some discussions with building control, but they arnt bad to deal with. Between us we devised an unavoidably complicate pipe layout when I added a wetroom upstairs a while ago which works perfectly... even though you wouldn't imagine it would! Builing inspector was impressed!

Its good to get as many peoples thoughts on things as its the best way to get the best solution, no one person can think of everything (not even building control! )

Cheers.

 

[reds42]

Although having read what I just wrote a thoughts occured to me...

Is it possible to rod round a long radius bend and so negate the need for additional rodding access to the run under the house other than the existing access chamber?

Its not a very long pipe run.

 

[dilalio]

When you put the basin in, put a trap in that has a built in admittance valve.

 

[Hugh Jaleak]

I've never tried getting rods around a long radius bend, (although they should go), as I'd be wary of putting a jet up there. To be honest, I'd still go for the chamber externally, even if a 9" mini chamber, (depending on invert depths), you really don't want to be clearing out a blocked sewer from a WC internally if you can avoid it.

Bring in the stack on a junction and fit a rodding eye at the base of the stack, if worst happens, you have access there.

 

[reds42]

Had a chance to take a closer measure up of where the pipes would run today and found the angle for the turn outside would end up not far off 90 degrees.

After a bit of searching I found I could get a swept 90 degree mini access chamber which will be perfect for access but also provide a nicer flow than a multi inlet ones (Hadn't realised these existed).

Many thanks for the ideas.

 

[Nige F]

And @ a good price too

 

[reds42]

And @ a good price too

I was pleasantly surprised by the price!

 

[Nige F]

Thinking on ..... I do remember seeing an Osma one once - @ a silly (typical Osma. price)

 

[rules&rulers]

Iirc the osma ones are 305mm diameter,dont know why thou.

reds42 have you contacted building control yet ? some can be helpful some not so. They usually (depend if they are very busy,lax or not bothered) need notification before work starts.

Last time doing a similar drain extension they told me as its a minor alteration just get the work carried out by a competent person on a competent persons scheme.

Good luck.

 

[Hugh Jaleak]

Diameter is down to the individual manufacturers, Osma no doubt want to be different so their chambers aren't compatible with anyone else, so if a new cover is needed for example, you have no choice but to buy Osma.....

Osma have done a range of mini chambers for some years, it now seems the large concrete manholes are being made off site to required angles, and just lifted into position on site. The art of shuttering up to form the channels, and then finishing with Grano benching, will soon be lost I sadly suspect.

 

[reds42]

Iirc the osma ones are 305mm diameter,dont know why thou.

reds42 have you contacted building control yet ? some can be helpful some not so. They usually (depend if they are very busy,lax or not bothered) need notification before work starts.

Last time doing a similar drain extension they told me as its a minor alteration just get the work carried out by a competent person on a competent persons scheme.

Good luck.

Not yet, still figuring out exactly what I'm after doing and how much its going to cost and if I have enough cash to hand yet.

I tend to get a bit fixated on doing a better job than stritcly necasary and the price always end up more than I initialy imagine. Spent alot more on my wetroom project than I envisaged... I mean... it would be rude not to have that ceiling mounted bluetooth audio system...

Was searching for ideas and came across this which I though was a nice layout idea (wonder how they fitted the basin waste). But I'd like a short projection wall hung pan therefore also need a frame (money), maybe some nice tiles for wall and floor (more money), maybe a nice piece of slate for the shelf (yet more money), and before you know it I'm very poor..