Sanitary Sanity Check

[i_am_fubar]

I'm currently in the process of re-modeling the bathroom. This will involve a re-route of the waste plumbing. My plan is currently as follows :

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• i_am_fubar
• 21 Oct 2013
• 1

Bathroom is above, garage is below.
Red pipes are 110 Waste.
Green pipes are 40 / 32 waste.

Issues / questions to date:
1) AAV's can only compensate for low pressures in the system. What causes / work arounds are there for high pressure? Would the other stack vents on neighboring houses handle it?

2) The AAV will double as a rodding point, but would it be worth fitting another rodding point in the vertical run in the garage?

3) With this plan, the basin couples into the top of a branch. Is this acceptable? Will it create a Venturi and suck the basin trap? Are there any adaptors to couple 40 /32 waste inline to 110?

4) Any other problems with this plan anyone can see?

Cheers,
Fubar.

 

[Hugh Jaleak]

Bear in mind an AAV will only allow air into the system, it wont allow any positive pressure to escape. I'd be wary of removing an existing open vent, especially if there isn't another on the property. WC is unlikely to pull the basin trap as the AAV will allow air in when WC is flushed, but any positive pressure will be looking for an escape, and may 'bubble' back through one of the traps.

Inline adaptors are available to couple 32/40mm to 110mm, may need to use the underground drain version, fine as long as it wont be exposed to sunlight. Vertical pipework is unlikely to block, provided access is available to the underground run from the base of the stack then I dont see the need for any additional rodding points on the stack.

 

[i_am_fubar]

Cheers Hugh,

I don't really fancy moving the vent due to the roof work involved.

I was playing with the idea of coupling in the new stack position to the old vent in the loft, but it's right near the eves of the house and access is close to zero.

Is there any way to vent out the side of the house providing your not near an opening window, or does it have to be above the roof?

Cheers,
Fubar.

 

[Hugh Jaleak]

Vent can be anywhere externally, but windows etc are avoided for obvious reasons! Above the eaves is also preferred to prevent obnoxious odours entering the roofspace.

Appreciate access is awkward in the roofspace, but the existing vent needs to be removed if not connected or you'll find rainwater getting through it.... Vent section can be reduced to 82mm diameter, or look at flexible vents if that would assist?

 

[i_am_fubar]

Cheers again Hugh,

If I did vent through the wall, it would be a wall that only has 1 window (that doesn't open) and one door, more than 3 meters away.

I note the regs are kind enough to say they have to be 900mm above a window that is within 3m, but it only details that on a flat wall, what if there is a window around the corner (external corner), how does that come into it?

We already have rain coming though into the garage *twitch*

Appreciate that venting above eaves is ideal, but is that something enforced by regs?

I considered flexible pipe, but won't the crenelations in it pool water on semi horizontal runs? (from the rain, not wet side plumbing).

Cheers,
Fubar.

 

[Hugh Jaleak]

I'd stick it out through the wall and keep schtum. If there's no opening into the building in the vicinity it's unlikely to give rise to any odour issues. Flexi was a thought to allow you to connect to existing vent through roof and then couple to a new vent run, not ideal in long lengths though, especially on horizontal runs.

Just a thought, but any reason why the junction on the existing soil cannot be rotated 180 ° and taken in the opposite direction for new pan position?

 

[i_am_fubar]

It's quite a small bathroom and unless we move the stack to the corner, there is only one, stupid, possible bathroom layout

I will measure all the dims around where the vent could come out and see how we stand. While I may have a rather low view of tax collectors, errr, I mean building inspectors, I do aim to keep to the regs

The wall I could vent out of (with the back door and un-opening window on it) is within 2 meters of the neighbors property, however, they have no windows or doors on that wall.

Will research position of stack vents a bit more. Worst case, I'll rip the ceiling down and run the stack up into the loft, then sideways and up through the existing vent.

Cheers,
Fubar.

 

[i_am_fubar]

Yea, re-read. 900mm above any opening within 3m... But part H doesn't seem to say anything about the vent within proximity to the eaves (would rather not loop around the roof if I run the pipe outside :/

Fubar.

 

[i_am_fubar]

Ah, hmmm, damn...

So, Part H, section 1.27:

Offsets in the ‘wet’ portion of a discharge stack should be avoided. If they are unavoidable then in a building of not more than 3 storeys there should be no branch connection within 750mm of the offset. In a building over 3 storeys a ventilation stack may be needed with connections above and below the offset. In buildings over 3 storeys...

So, my understanding here, is that if I kink my stack, as shown in my OP, I can't have anything coming into the stack within 750mm of any bend (above or below). Which really does throw a spanner in the works as all of my connections would be within that area

I'm hoping I've mis-understood what it's saying now

Likewise,

 

[i_am_fubar]

Also, part H seems to imply that branches have to be staggered when they meet the stack. If this is the case, why are boss points included in 110mm branches? :s

Fubar.

 

[Hugh Jaleak]

Opposing branches have a habit of blocking up, as discharge from one side can enter the other. Know of one instance where a waste disposer from a kitchen sink and waste from basin in ground floor WC were opposite. Basin waste was constantly blocking, eventually I was asked to cap off the basin connection to the stack and reroute the basin waste to an external gulley. (Never been a problem since!) Whilst bosses are provided on both sides of certain fittings, the expectation is only one side is used. (Installer has option of either side to make a connection, by simply opening required boss.)

Problem with bends in the 'wet part' of the stack is when a WC is flushed, it can effectively fill the stack, causing a slight pressure increase in front of the flow. When the flow gets to a bend the pressure increase can be sufficient to blow out traps on appliances. May be able to get round that by using a soil manifold.

 

[i_am_fubar]

So, I guess the soil manifold somewhat negates the venture effect or having perpendicular pipe joints, but how would it handle the positive pressure increase?

(I had no idea how complex waste plumbing was, having to brush up on my fluid dynamics )

I think we're going to keep the existing stack vent (boo) at this point and just have a branch for the WC. Seems like it could easily cause issues if we try and kink the stack.

Cheers for the help all the same, reading into this and from you help Hugh, I've got a pretty reasonable idea what you can do, can't do and may just be able to get away with.

Cheers again,
Fubar.

 

[Hugh Jaleak]

Manifold wont help with positive pressure issues, but is a useful solution when needing to connect wastes and avoiding the 'no connection' area opposite other branches. Glad to be of assistance, poorly designed soil/waste systems can soon start throwing up all manner of unpleasant problems. It never ceases to amaze me what some folks cobble together and then either look at you gone out when you tell them it wont work (never mind breaches half, if not all, the regs), or expect you to try and sort out without actually changing anything......

 

[i_am_fubar]

Check.

On the note of checking. Is there any sort of drainage check valve you can get? I want to connect a sink and washing machine in the garage (so probably through a manifold) to make a utility and don't really fancy getting poop out the plug hole if the stack blocks below ground level.

I've found (both as an engineer and working with others), that there are certain people who can see the systems and how things will interact. Seeing things like drainage, or plumbing, or electrics as a whole rather than a sum of parts. So while they may not know the regs, they can often see the pitfalls without being told them.

Cheers again Hugh,

Fubar.

 

[Hugh Jaleak]

HepVo valve will act as a non return valve for waste applications. http://www.hepvo.com/