Blocked house drains, unusual stack -alleyway responsibility

[yoocan]

Hi all,

A bit of background:

I live in a 1905 house with a combined system
I have a stack in the yard which is usually clear
The yard and surrounding area is paved
The corner of the yard has a blossom tree in it, diameter ~0.4m
There are no manholes, inspection chambers, or rodding eyes
The sewer is in the alleyway and there are no inspection chambers in the alley ( although there is one some distance away see below, red circle)

I have sketched a schematic of what I think the drainage is like, based on prodding around and a little digging :

The first image is from the building survey (UU), i've added the brown line and highlighted my house.

Does the schematic seem reasonable?
Why is there a stack in the yard?
Why does it appear to have a base, is this a sort of trap?
I can feel the invert of the incoming pipe with a prodding stick, why can I not feel the outlet at all?
The blockage is obviously past the last stack and maybe in the alleyway, however if I am at the head of the system; am I responsible for blockages in the alley?
Is it possible for the tree roots to have found its way into the system and blocked it?
The system consists of 3 hoppers a waste pipe and approximately 10m of pipework, if I was to replace the whole lot (and include an IC/rodding eye) how much would it cost roughly (materials only) and how long would it take 2 men?
Where would be the best place to put and inspection chamber or rodding eye?
How should I go about dealing with this problem?

Apologies that was quite a long one.

Any help would be much appreciated.

Kind Regards,

J

 

[Hugh Jaleak]

The building is pre 1937. Public Health Act 1936/37 puts sewers that serve more than 1 property into the remit of the sewerage provider, i.e. your water company. Are you the only property affected?

Stack has probably been added at some point to ventilate the system, you don't say if it serves an upstairs w.c., although you have shown 3 gullies on your plan a w.c. has a direct connection to the sewer, which is not shown unless its via the stack.

The "trap" you describe at the base of the stack could be an old gulley that someone has connected the stack into during the past. Ideally this needs to be replaced imho with a rest bend, stack will not vent the drain through a trap!

Possible that tree roots have got into the pipes but until you ascertain the location of the blockage it is impossible to pinpoint the cause. Could be fat build up, sanitary towels, collapsed pipes... I think it unusual there is not a manhole near the road, (unless its been buried), drains in that era usually had an interceptor just prior to the sewer entering the road. These are a classic cause of problems.

If the system has worked ok prior to this incident why spend money replacing it? May require excavation if the blockage cannot be located and a manhole on your property will not go amiss for future reference but you may be spending for the sake of it if the pipework is still serviceable. Cost of replacement will depend on access, depth etc. (My property was built in 1896, there's 20+ houses on the run and we've not had any problems, other than a blocked interceptor.)

 

[yoocan]

Thanks for the reply.

A friend came round today with a pipe bending spring on a length of copper pipe and unblocked the stack! I did'nt think it would work since I had no luck with caustic soda and plunging it with a mop.

It would seem that the stack is connected to the public sewer via a P/U type bend and this must have been clogged up.

On the plan I should have mentioned that the left most brown circle represents a soil pipe (upstairs WC) which I think is at the head of the system, would that mean there is'nt a direct connection to the sewer.

I would like to prevent this happeing in the future, or at least provide a simpler way of maintaining the system.

Would you mind elaborating on your suggestion:

Ideally this needs to be replaced imho with a rest bend, stack will not vent the drain through a trap!

Or if any one else has any ideas on where a rodding eye or inspection chamber should go that would be greatly appreciated.

 

[Hugh Jaleak]

From your description I thought there may have been some kind of trap at the base of the stack. If there is a water filled trap at the base of the stack then air from the drain will not be able to pass thus not ventilating the drain.

A rest bend is a long radius 90 deg bend, often having supporting 'nibs' on the rear, (Screwfix item no. 12719), it allows the flow to gently sweep round the bend into the drain. (Use of these at the base of a stack is now a requirement of building regs.) Use of a short radius bend can cause compression of the air in the stack when the w.c. is flushed, the waste hits the bottom possibly blowing out water seals in traps connected to the stack.

I would locate a manhole either on one of the junctions in your yard or on the run just before it exits your premises. This will allow future inspection, at least if the pit on your premises is full, it points to the problem being off site, i.e. in the alleyway. Installing a manhole outside your premises would be down to the water authority I would think. A rodding eye in this situation, whilst serving its purpose allowing access, wont help you pinpoint location of the blockage. Seen people before shoving 20m of rods down a drain when the blockage is 100m away and the system has backed up to that point.

Also you may want to install a access point at bottom of your stack before it goes underground. This will allow access for inspection or rodding, stand well clear if you undo it when there's a problem! (Screwfix item no. 18079. Sorry, dont know how to post the links.)