Common foul waste drainage and extension

newbie23

Hi all especially the architects/engineers out there, I could really use your advise!!!

I'm building a 20sqm single storey extension and on good advice I contacted an architect I have used previously and he said that what I really want is an engineer as my main concerns are drainage, removing back wall of existing structure and building off a neighbouring boundary wall. Anyway, I'm currently waiting on quotes from engineers but before I take on an engineer, I'd like to know a bit about private foul waste drainage and best practice for building over them (I've a Masters in Science and I like to know a bit about this and that ).

I live Dublin and a shared foul sewer drain runs no more than 4-5 ft away from the back wall of my house and the extension we are building will be at least 12ft and we will have to cross this drain in order to get full width. We also have a inspection chamber, if that's what it's called, at about 5ft from back wall (looks like and open half pipe in a large rectangular opening). So prior to going down the engineer route, I had plenty of quotes from builders for my extension and each time I asked about what they will do about drainage they all had a different idea as to what they would do. So I thought I'd see if anyone would like to advise as I'm sure that even engineers advise would differ and I just want the best job and to understand the problems that could arise as I can imagine crossing a drain at any stage would have it's implications but there are alot of houses extended in my area so I reckon it has been done without too many problems. So here's the what the builders had to say:

1. Two out of five builders were leaving the existing drainage as it is currently and routing all new waste water drainage back under the house to the common drain but giving us access to the main line within the house using this inspection chamber. They would also leave the existing stack that runs down the back of our house within the property. I don't like the sound of this one!!!
2. Two builders would turn the shared drain where it enters my property to route it inside our foundations and bring it out where our extension finishes, here is would collect waste water from the kitchen extension and foul waste from a new stack run from the old house down the inside of the parapet wall and down the side of the extension and run this drain back under the house to connect back with the neighbours drain under their extension. Rodding access would be in the garden. But surely the more bends in the system, the more likely blockages leaving me the culprit in causing problems?
3. One builder said he would remove this inspection chamber and reconnect the 2 pipe ends and saddle our drain onto this point, leaving all waste still running in a straight line and our new drain would be a T type structure that would run across the front of our house and after collection would connect to the main drain through a single pipe. We would have rodding access to the pipe that would run under our house. Sounds good, but I have a fear of not having access to this main drain that collects our neighbours waste.

Dilemmas, Dileemas, I have familiarised myself with Building regs but can't work out what's best as all are a possiblity but all have downfalls from a drainage point of view.

con1982

Having not seen the existing drains or proposed plans, I can't comment on your particular project.

Generally, it's best to leave the common drain as is. I'd seal the manhole if it within the extension floor plan. Construct a new manhole upstream. I'd run all new drains externally and saddle into the common drain (or connect into upstream manhole if levels permit).

It's possible to use a double sealed manhole cover and recess finishes avoiding the need for a new manhole, but I'd avoid this unless there is absolutely no alternative.

Your engineer will know best once he/she sees the job.

A fella called fish

If this is the old shared foul running through the back gardens, then it is no longer council taken in charge by the council and is 'shared' between everyone connected to it. As such, you have no right to divert this drain, strictly speaking.

I have only diverted one of these drains on one occasion because it was damaged and caused an existing extension to settle & crack.

The Engineer will give project specific advice, however I would leave well enough alone if its in good working order. Provide bridging details at foundation/rising wall level where your foundations cross the pipe in accordance with Engineer's requirements.

sydthebeat

Have you been advised that what you are doing requires planning?.... Because it does....

newbie23

Thanks for the advice guys. I thought that saddling the existing system would be best I'm just worried about removing access to the main drain line that collects from all houses as we would have no way of rodding this drain if it became blocked under our extension, only by gaining access from a neighbours garden. I really wouldn't like access inside the house.

sydthebeat wrote: »

Have you been advised that what you are doing requires planning?.... Because it does....

How so sydthebeat? This shared drain is not maintained by council, it is a private drain which we maintain amongst the houses that it collects waste from. My neighbour has built an extension next door and did not get planning.

sydthebeat

newbie23 wrote: »

How so sydthebeat? This shared drain is not maintained by council, it is a private drain which we maintain amongst the houses that it collects waste from. My neighbour has built an extension next door and did not get planning.

water services act 2007

section 104 : building over pipes

104.— (1) A person shall not, except with the consent of a relevant water services authority and following an application for the purposes of this section to that authority, erect or commence to erect, or cause to be so erected, any structure—
(a) over, or
(b) so close to as to cause a risk to, or interfere with, the structural integrity of or access to, a sewer, drain, water main, distribution system, service connection or related accessories which are owned, controlled or used by another person.
(2) The obligation in subsection (1) shall apply notwithstanding any provision in any other enactment in relation to control of development, building standards or practices, or any related exemptions.



I have highlighted the important parts.

Basically, any extension over any shared sewer or watermain looses its exempt status.

newbie23

Ok sydthebeat, you had me worried there!!

I got onto the Drainage Department of Dublin City council, who gave me the email address for one of their engineers who looks after extensions and drainage. I have sent him an email asking him to clarify this for me and asking for advice in this instance.

In the meantime, I got onto the planning department who put me through to building control who in conjunction with the drainage department have advised me that this foul drain is not controlled by their authority and is in fact a private drain, the way they put it "It is not on their map". They said once I comply with building standards, I can in fact erect a structure over them.

I read this act, and while I've no law degree the Water services act could be used if I caused nuisances with my construction like a drain collapsing as it was not properly bridged but that section does refer to building on or over, I will wait until the engineer replies in an email format so I can get a better idea of what they are talking about. I wonder could I get an official letter from them saying that they do not see themselves as having authority over this particular section of drain at this time ??? After reading the act, I know they can take authority over any drain at any time but if I had this then my building would still get an exempted development cert.

sydthebeat

Id be most grateful if you could give us an outline of the DCC engineers response when you get it.

Its my current understanding that the law reads as i have outlined, and if i misinterpret then its better to be proved otherwise.

sydthebeat

newbie23 wrote: »

.....
In the meantime, I got onto the planning department who put me through to building control who in conjunction with the drainage department have advised me that this foul drain is not controlled by their authority and is in fact a private drain, the way they put it "It is not on their map". They said once I comply with building standards, I can in fact erect a structure over them.
.....

in all due respect to "building control" in my experience if the legislation falls outside of the building control acts they tend not to be interested / educated to answer.


this is a query for your local authorities water services section to be able to give you a definitive answer on.

con1982

I didn't realise the wording said "drains used by others".

The feeling I got from council engineers is, that the council dont own or maintain these drains so they don't want to know.

I've worked on dozens of jobs where the common drain was bridged by the structure. I suppose if an angry neighbour got wind of the planning regs you might be in a grey area.

sinnerboy

My reading of the Water Services Act text is that it is not saying "if you build on/close to a shared drain - you need planning permission" rather it is saying that "even if your development is exempt from planning - you still must obey this law".

So whereas even if the OP satisfies all other requirements to build an extension which is exempt from planning permission , the Water Services Act requires that consent be obtained from "a relevant water services authority".

In my experience of dealing with DCC engineers "on the ground" with respect to rear extensions requirements typically include

Build over the drain - do no not divert it
Provide lintols over the rising walls where the drain passes through ( that part of the walls starting at the top of the foundation and ending level with the floor level )
Fully encase the drain in concrete to down level with the new foundations
Provide rodding access to the drain ( complicated to explain in text only )
Provide rocker connections at terminations of the extension ( complicated to explain in text only )

OP - you are doing the right thing is seeking an engineer. Internet forums are by nature a limited resource.

sydthebeat

im certainly open to correction, but my reading of:

The obligation in subsection (1) shall apply notwithstanding any provision in any other enactment in relation to control of development, building standards or practices, or any related exemptions.

means the build losses its "exempt" status.

Specifically, the "control of development" and "any related exemptions" parts.

I think ill badger my local planning and water services section in regard to this.

Dubstar07

Hi all,

Apologies for dragging up this again. I'm facing into a similar situation myself with a new extension looming.

OP - did your build proceed & if so how did you overcome the 'shared' drain chamber issue?

Syd - did you obtain any insight from the relevant authorities as to the interpretation of the regs?

Thanks, Dub