Drainage Proposals

[Bonce]

Hello All,

I have been asking a couple of drainage questions over the last couple of weeks (thanks for all the useful replies and information very much appreciated). All this has been with a proposed extension in mind.

I think I am going to go ahead and its the drainage design which seems to be proving most troublesome to get my head around so I wonder if people would mind taking a look at my current drainage on the plan below and then my proposed drainage and answering a few queries I have.

Thanks in advance for any time spent and any opinions and information people can supply.

Image 1 ==>

Existing

• Bonce
• 11 Feb 2012
• 1

Ok so the first image is of my current situation. Its a plan view of my semi-detached 2 storey house, front at bottom of diagram rear at top. Party wall and neighbours would be on the right of the diagram. The yellow shaded area is the cavity wall proposed for a side extension (single storey).

On this you can see the current location of the SVP (left hand side of pic). Also marked in red line is the drain from this to an existing manhole. This manhole is a line of manholes that run down the backs of the properties on the street and all connect up (direction of flow left to right on diagram - sorry forgot to put that on). Realise that the drain from the SVP runs against flow but its just the diagram and think this is overcome by shallow bends so at the manhole it sweeps in correct direction of flow.

There is also a short gulley connected into the sewer (marked in blue at the left corner of the current house). This takes rain water and waste from upstairs bath and wash basin which all empty into an open hopper half way up my rear wall (realise from other post today that open hoppers are now not considered good practice and dont comply with part H).

Image 2 ==>

proposed

• Bonce
• 11 Feb 2012
• 1

Image 2 is what I am thinking I MAY be able to do to conform with current regulations etc. In this diagram you will see that I have a proposed utility with a WC and basin (marked (3)). I will also be looking to relocate my boiler to this room and therefore will need to deal with condensate from that.

At point marked (1) I intend to remove the current manhole and have a connection at this point to the new WC in the utility. Shown with the blue line.

At point (2) I want to put a new manhole and relocate my SVP close by as shown in black. I will remove the existing SVP and drain when doing ground works on the extension.

OK so now (finally) the questions! Thanks if you got this far.

1) At point marked (4), bottom left of proposed plan I have shown a rodding location. I have extended the run from the WC to the front of the extension to allow this run to be rodded as at point (1) there will no longer be access. Is this ok/necesary? or can I allow a rodding point in the utility room somehow (stub stack)? I wasn't quite sure if access was needed for my neighbours if I was away or whether this part of the drain would be considered non public.

2) Would I need any sort of ventilation on this WC drain? Stub stack and AAV (air admittance valve)?

3) At point marked (2) I intend to relocate my soil pipe. My question is... the gulley marked in Image 1 currently takes rain water and the wash basin and bath waste from upstairs as well as downstairs sink and washing machine... i.e. rain water and grey waste go into same gulley. This gulley will not be able to be left in place and so I had intended to run all the above into the new SVP. Is that OK i.e. is it ok to run the waste from sinks etc and rainwater from guttering into SVP? It does all end up at the same drain running along the backs of the houses in red at the moment.

4) In the Utility where I have shown a WC and sink I also want to put a washing machine and relocate my boiler, I was thinking that this could all discharge into the WC using a connection something like this ==> http://www.mcalpineplumbing.com/boss-pipe-for-use-with-wc-connectors.html would that be ok? i.e. the condensate wash basin and washing machine run into a 40mm branch pipe and then into that connection? I understand that the connections and pipe taking condensate from boilers need to be made of material to withstand particular pH values as per part H.

5) Final question ... promise! Any general problems in any way with what I propose from a regulations/ease of build/poor design point of view. I realise that for the point (1) that I will need to get local water company involved as it will require some sort of build over agreement, and that all this will need to be checked out by the BCO but just wanted to ask those with far more knowledge than myself up front. That way I sort of know where I am when I talk to a local builder and don't feel such a donkey!

Sorry again for such a long post and many thanks in advance for any help. As always much appreciated.

Bonce

 

[Hugh Jaleak]

1. Where new drain for W.C. connects i'd fit a manhole to provide rodding access along branch to W.C. position. Drain wouldn't then need to go further than W.C. position. This chamber should be fitted with double sealed, screwed down, internal cover. Should run ever block its a lot easier to work from a manhole, at least you can then see what comes out and hopefully catch it to prevent it causing further issues down the line.....

2. W.C. can be connected directly to drain provided the depth from the invert of the drain to the crown of the W.C. trap is less than 1.3m. Stub stack can be fitted though if you wish to connect wastes to the drain. (Fit an AAV if using a stub stack.)

3. Wastes ok into SVP, rainwater will need to be kept separate though to as far as ground level, discharging into a (new) trapped gulley. SVP needs to vent above the eaves. (Connecting rainwater to a Soil pipe could allow odours into the roof space.)

4. Should be fine. Condensate needs to be run in plastic pipe, although usual ok once its at the stack or drain as other discharges will dilute it.

 

[Bonce]

Hugh Jaleak - once again thanks very much, you seem to be answering all my posts. Got a couple of follow on questions if you dont mind: (yours in blue mine in red)

1. Where new drain for W.C. connects i'd fit a manhole to provide rodding access along branch to W.C. position. Drain wouldn't then need to go further than W.C. position. This chamber should be fitted with double sealed, screwed down, internal cover. Should run ever block its a lot easier to work from a manhole, at least you can then see what comes out and hopefully catch it to prevent it causing further issues down the line..

I'm slightly confused about this..... are you saying you would put a sealable manhole where I have indicated the current position of the manhole i.e. in diagram 1 in red? I am under the opinion that I cant have the manhole inside as its a public sewer and as such I must allow rodding access for my neighbours etc even if I am on holiday.... when I had the BCO in quickly for another job he menitoned this. This was the reason for extending the drain and running a rodding point to the front. The floor will aslo be a suspended floor at this point (sorry forgot to mention this).


2. W.C. can be connected directly to drain provided the depth from the invert of the drain to the crown of the W.C. trap is less than 1.3m. Stub stack can be fitted though if you wish to connect wastes to the drain. (Fit an AAV if using a stub stack.)

If it's allowable I'll think I will try and avoid a stub stack and connect waste using a pan connector with 40mm connecting into that. Do I have to have a stub stack if I connect wastes from basin/boiler/washing machine?

3. Wastes ok into SVP, rainwater will need to be kept separate though to as far as ground level, discharging into a (new) trapped gulley. SVP needs to vent above the eaves. (Connecting rainwater to a Soil pipe could allow odours into the roof space.)

Ah so thats why you cant put guttering into the SVP. I wasn't sure if it was allowable but couldn't remember where it said it in the regs or think why it would cause issue. With the SVP I understand about the venting requirements being 900mm above any opening within 3m but have a general question re AAV. Could I not simply fit one at the top and then would it matter that it was within 900mm of an opening? I have read lots on posts about AAV usage inside but don't see anywhere that they are allowed to be used outside. I ask this as in time I am thinking of having a loft conversion and I would therefore have to somehow take my SVP around the eaves and then finish above a new dormer window. That would be a bit of a job but if an AAV can be used it would not be an issue.

4. Should be fine. Condensate needs to be run in plastic pipe, although usual ok once its at the stack or drain as other discharges will dilute it.

Excellent thanks... so the pan connector I show would be ok as long as everything and the connector is suitable for condensate (pH value)?

Once again huge thanks, much appreciated.

 

[Hugh Jaleak]

1. I would be inclined to keep the existing manhole, current connection to existing SVP could be utilised for new connection to W.C. Manhole should be ok internally provided correct cover is fitted, plenty like that about!

Ultimately if you are away (or just out!) and access is needed to the manhole then its tough! Any blockage in that vicinity should be able to be dealt with from 'either side', in the neighbours properties. Suspended floor wont cause an issue, drain should be under the oversite anyway, encased in concrete for protection.

2. Should be able to connect wastes via the pan connector. Alternative option could be a soil manifold set at floor level, these will accept several wastes.
3. AAV may be permissible but regs state the highest point of the drain must be ventilated. BCO may insist you keep one vent on your property. If AAV is allowed you would need the external version. (More expensive!)

4. Condensate should be fine in plastic, cant see any issues. Metal pipework is to be avoided for any condensate drain as condensate will corrode the pipework.

 

[Bonce]

Thanks Hugh Jaleak and not just for this post but all the others over last couple weeks you have been a great source of knowledgeable info.

Going forward I'll chat more to the BCO before submitting my full plans application and try and get his definitive answer about what he would want.

Point taken about the existing SVP/drain.

Ta again.

 

[Hugh Jaleak]

BCO's generally helpful bunch, better to work with them than try and pull wool over their eyes! Their interpretation of things can vary so it's always a good plan to discuss your proposals beforehand, and ensure you get it right first time. Best of luck!