Building an extension near a main drain

ravendude

Hello,
I'm wondering are there any building regulations wrt how close you can build an extension near a main drain (servicing a large number of houses within the same estate)? The drain is running through the property (there's a legal right of way for it apparently). There are no manholes involved as far as I can see. Could you build up to it, perhaps with the side path around the house being build over it?
We'll get an engineer to look obviously, but would like to hear as many opinions as possible..
Any advice or experience appreciated.
Thanks...

sydthebeat

i have often seen cases of building over public sewers such as these. just ensure benching etc is all in accordance to "site development works" DOEHLG publications.

onq

ravendude wrote: »

Hello,
I'm wondering are there any building regulations wrt how close you can build an extension near a main drain (servicing a large number of houses within the same estate)? The drain is running through the property (there's a legal right of way for it apparently). There are no manholes involved as far as I can see. Could you build up to it, perhaps with the side path around the house being build over it?
We'll get an engineer to look obviously, but would like to hear as many opinions as possible..
Any advice or experience appreciated.
Thanks...

This depends on whether or not this is a public or a private drain.

If its a public drain:

No, you cannot build near it or over it - its actually illegal under some 1948 act the title of which I cannot remember tonight.
Contact your local authority to verify all this, but IIRC you must leave the working tolerance for a JCB to dig up the drain.
Usually this results in a 6M ROW centred on the drain 3M either side.
I've inspected two sites for two different clients and advised on a third.
The two I inspected had potentially beautiful side garden sites until you found out about the drain, which in one case was a 1200mm SW culvert or an old underground river.
The one I advised on had already been commented on by a colleague and his client had bought on the strength of his advice that they could build over it.
Wrong advice, as it turned out.

If its a private drain

Yes, it may be possible for you to build near it, and perhaps over it, depending on what, if anything, the house leases in the area have to say about a wayleave for services across the respective sites.

Many 1960's estates had private FW or Combined drains in their rear gardens and your only obligation AFAIK is to not interfere with the outfall i.e. not block it.

You should ask your solicitor to check your title documents and advise on all of this, but as a courtesy you should inform your neighbours and advise them of the works.

Its then up to your professional advisors to design the works to ensure that
(i) any future blockage of the drain can be rodded
(ii) any potential damage through settlement or foundation loading is minimized or avoided altogether by taking measures to protect the drain where it passes through new rising walls and/or under or near the new building and
(iii) there is no disruption to the outfall of the drain during the course of the works - this may involves designing a temporary holding tank while the route of the drain is altered or new manholes installed either side of the new building

ONQ.

All advice on Boards.ie is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent persons should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
My best advice is that you should retain competent professionals to advise you on these matters.

DOCARCH

Normally drainage within a site is private but if you are aware of some sort of wayleave, then its most likely a public sewer. Check title deeds and with the Council - if the sewer is serving a number of houses or is public, then it should show up on Council maps. ONQs advise/comments are correct.

I dealt with a house recently where there was a public watermain in the rear garden (not too far from the back of the house). My clients wanted to extend but the Council insisted no development could take place 3 metres either side of the pipe. Pretty much scuppered plans for any extension!

ravendude

Thanks again ONQ et al for the clear concise advice.
I'm pretty sure this is a public drain or an equivalent. It really looks like 3 metres has been deliberately left there, and its coming to light now that there are in fact building restrictions as well. So it looks like an extension is out, this we can live with (its a prospective house purchase).
Aside from the limitations with building extension, is it of major concern having this in your garden? ie. What happens if it bursts? or needs to be dug up? who manages/repairs it? Would there be any insurance implications? Is there any risk of it contaminating the foundations?
Maybe all my questions are an overreaction, and its not too uncommon, I'm not sure....
Again, any thoughts appreciated.

onq

ravendude wrote: »

Thanks again ONQ et al for the clear concise advice.
I'm pretty sure this is a public drain or an equivalent. It really looks like 3 metres has been deliberately left there, and its coming to light now that there are in fact building restrictions as well. So it looks like an extension is out, this we can live with (its a prospective house purchase).
Aside from the limitations with building extension, is it of major concern having this in your garden? ie. What happens if it bursts? or needs to be dug up? who manages/repairs it? Would there be any insurance implications? Is there any risk of it contaminating the foundations?
Maybe all my questions are an overreaction, and its not too uncommon, I'm not sure....
Again, any thoughts appreciated.

Hi Ravendude,

You're very welcome and congratulate yourself on being wise enough to seek advice before purchase.
The width is usually 4-6 metres clear and preferably six, i.e. 3 metres either side of the assumed centreline of the drain.
I say assumed because drainage can throw up some surprises when you trace routes and outfalls and council records can be sparse.

Yes, the new queries you're raising can all affect your enjoyment of the dwelling and can cost money and time to put right.
Who foots the bill for the repairs to the drain is one thing - who compensates you for time and disturbance and mess quite another.
To better assess the condition of the pipe under the house plot open up the nearest manhole, inspect it visually and dip it for depth, then go upstream and dip the next one.
Falls are supposed to be constant between maholes and if you know the levels of the ground you can interpolate how deep it is under the site.
This can cause concern if you find that the pipe falls within the 45 degree angle rule of thumb for protectingdrains from foundation loads and piking down suggests there is no protection.

If you suss out where the two manholes downstream and upstream are and you find you don't have line-of-sight between them one or two other reslisations may strike.

(i) there is a tree or big bush or walling in the way, under which this piple must pass
(ii) there is no way the pipe can be a straight run between manholes - either its curved or it passes under a house.

All of the above conditions can give rise to problems

1. Settlement from the foundation loads, affecting the self-cleansing rate of fall.
2. Interference in the pipe from roots or the foundations of walls if its not properly bridged by a lintol or arch with a tolerance.
3. Inadequate manholes for inspection or cleaning on a curved run.

The issue isn't what might affect you in terms of usage but how might this affect your sale price in the future, but discovering the history of the place is not rocket science.
Look for the remnants of past overflows, staining at or near manholes, bits of paper debris in the back garden, "tide" marks along walls that weren't cleaned off.
Ask locals if there are drainage problems, especially:

(a) those living near the manhole covers as they will have seen them overflow and
(b) those upstream of the curve/wall/tree whose house drainage may back up by obstructions downstream.

Blocked drains aren't cheap to continually free - if you have to call a specialist company out twice a year it can be €175-300 a pop depending on whether it goes over the hour.
The manhole doesn't have to be on your site, the overflow can be upstream and run down onto your land.
This can lead to problems if you have inconsiderate neighbours upstream who put stilly things like diapers and cooking oil down the drain which by-pass your site, get "caught" just beyond it and cause a blockage that affects your property.
In that regard it might be useful to suss out the local residents association on this matter as well as ringing up the Council and local drain-clearing firms, saying you think you might have a problem and do they know of any in this area

One thing to keep in mind evne if there are no actual problems with the drain is on the buying and selling front - there is a negative psychological and therefore financial impact when someone looks at a site thinking "yippee" at the thought of being able to get a house in the side garden later on only to find their empire-building hopes are dashed.
The chap I posted about above who had the 1200mm wide SW Culvert/underground watercourse to the side of his house is the exception that proves the rule.
He had already bought the property by the time I was brought on board.
Luckily enough I did my due diligence before accepting the instruction to obtain permission.
I think he's still living there, having failed to beat down the asking price as he might normally have done because he thought he was getting a good deal

ONQ.

All advice on Boards.ie is remote from the situation and cannot be relied upon as a defence or support - in and of itself - should legal action be taken.
Competent persons should be asked to advise in Real Life with rights to inspect and issue reports on the matters at hand.
My best advice is that you should retain competent professionals to advise you on these matters.

ravendude

Thanks again ONQ,
I spoke to my engineer who didn't seem overly stressed out about it and he will do a site visit to assess, he did mention that the first thing to look at were the access points, as this is where a blockage will force a spillage.
He seemed to suggest that it wasn't an uncommon scenario.

I guess the broad question I would have now, - is whether this is a reasonably common scenario, particularly is it reasonably well understood one.
ie. The drain seems to be reasonably away from the house (at least the 6 metres you mention).
So, is it common enough for estates to have storm drains going through part of the garden, - or is it so unusual that something could easily be overlooked in assessing it?.....can it be adequately derisked, or is it a case of simply "run to the hills"
Thanks again...

onq

ravendude wrote: »

Thanks again ONQ,
I spoke to my engineer who didn't seem overly stressed out about it and he will do a site visit to assess, he did mention that the first thing to look at were the access points, as this is where a blockage will force a spillage.
He seemed to suggest that it wasn't an uncommon scenario.

I guess the broad question I would have now, - is whether this is a reasonably common scenario, particularly is it reasonably well understood one.
ie. The drain seems to be reasonably away from the house (at least the 6 metres you mention).
So, is it common enough for estates to have storm drains going through part of the garden, - or is it so unusual that something could easily be overlooked in assessing it?.....can it be adequately derisked, or is it a case of simply "run to the hills"
Thanks again...

I know of two three estates where Surface Water sewers serving as a public mains pass through private gardens.
I think you should discuss the possible risk with your engineer and the local authority who may be able to comment on past problems in the estate including flood risk.
Where the mains is a Surface Water sewer a risk may arise from flooding caused by events upstream, for example a new development where the SW system feeds down into yours.
Where there is an increase in seasonal rainfall in terms of intensity or extended duration and repeat extended duration, the possibility of flooding and surcharging arises
Where increased rainfall causes groundwater levels to rise and where the pipes have poorly sealed connections, the possibility of surcharging also arises in foul sewers.
As you can see there are foreseeable but unquantifiable risks associated with the weather we've been having and also upstream developments.
So its possible estates without previous flooding or surcharging problems may experience them in the future.
Flooding issues may also arise in relation to Combined Sewers, which carry both surface and foul water.
This is a general and by no means exhaustive comment on the risk.

FWIW

ONQ.

ravendude

onq wrote: »

I know of two three estates where Surface Water sewers serving as a public mains pass through private gardens.
I think you should discuss the possible risk with your engineer and the local authority who may be able to comment on past problems in the estate including flood risk.
Where the mains is a Surface Water sewer a risk may arise from flooding caused by events upstream, for example a new development where the SW system feeds down into yours.
Where there is an increase in seasonal rainfall in terms of intensity or extended duration and repeat extended duration, the possibility of flooding and surcharging arises
Where increased rainfall causes groundwater levels to rise and where the pipes have poorly sealed connections, the possibility of surcharging also arises in foul sewers.
As you can see there are foreseeable but unquantifiable risks associated with the weather we've been having and also upstream developments.
So its possible estates without previous flooding or surcharging problems may experience them in the future.
Flooding issues may also arise in relation to Combined Sewers, which carry both surface and foul water.
This is a general and by no means exhaustive comment on the risk.

FWIW

ONQ.

Sounds risky enough taking all things into account!

sinnerboy

Not really .

If its a public drain you can't build over or near it ( usually 3 metres ) . End of story .

A 10 minute visit to your local authority drainage department and examining the map will answer the question - is it public or private .

If its a private drain you can build over or close to it ( with proper guidance ) . A drain run along rear gardens in estates is not a unique feature . If this alone is putting you off the property you will search for a long time .

ravendude

sinnerboy wrote: »

Not really .
. A drain run along rear gardens in estates is not a unique feature . If this alone is putting you off the property you will search for a long time .

Ok, that puts it in some context I suppose, thanks, its pretty much a public drain and we have come to terms with the fact that it won't be possible to build near it.
I guess, since acknowledging this, I've been trying to get a feel as to how common/uncommon it is to have drains in private gardens. This does seem to be fairly significant drain though, servicing a large section of a large estate. It is several metres away from the house which is a good thing in itself I suppose. The plus side is that we get a bigger garden than pretty much everyone else I suppose, although we can't build there.

onq

ravendude wrote: »

Sounds risky enough taking all things into account!

Well, its pretty straightforward as Sinnerboy has said.

The biggest issue is whether its a troublesome drain or not.

It it is and its Public, the Council undertake the repair - it costs zero.

It it is and its Private it has to be privately resolved - it may cost a lot.

That being said, buying into any 1960's estate in any area may throw up similar issues.

Its a bit like buying a Merc or an old house - you decide to live with the issues if you're going to have one.

FWIW

ONQ.