Interesting CON29DW situation

Dogbolter

Hi all - first time poster, so take it easy... :-)

We purchased a property in April 2013 - one of the primary factors in our decision was that the plot had plenty of scope to build a detached double garage, convert existing integral double garage, put a conservatory on the back etc.

As part of the search process, we had a CON29DW produced that showed no public sewers or mains infrastructure within the boundary of the property.

Having got as far as gaining planning permission for the detached garage and integral garage conversion, we have just submitted the application for building regs.

Several of our neighbours have recently had some problems with blocked sewers, so given the CON29DW report, you can imagine our surprise that Thames Water sub-contractors requested access to our property to lift a manhole cover to help clear a blockage to a public sewer.

I've looked at the original deeds (built late 1960's) and although I can't read the key, there looks to be a public sewer that serves 4 original houses (now potentially about 10 after development about 7 years ago) that runs parallel with the back of my property (about 5 feet behind and under the area we may want to build a conservatory in the future) but then looks to potentially cut diagonally under the land where we are going to build the detached garage!

Now, I'm fully expecting TW not to raise any concerns via the Building Regs process, as they have access to the exact sewer maps that were used in the CON29DW report - I've spoken initially to the Sewer Operations team and they confirm that their maps show no public sewer.

Therefore, unless their sub-contractors are shockingly useless, I have a public sewer within my boundaries that could well be impacted by my approved development, but it's unlikely to be picked up at all through the formal building regs process.

However, there is obviously a risk that maps will be updated whilst we reside at the property, causing problems when we eventually come to sell, especially if no build over agreement is in place (how do you gain build over approval for a TW asset that doesn't officially exist?!?).

So... I believe that TW have unlimited liability for resolving the issue if it is proven that the CON29 report was incorrect.

My thinking at the moment is to try and work with them to get the sewers accurately mapped in the first instance so that we know where we stand.

Obviously, I'm not going to want to alter our building plans, pay any additional indemnities, fork out extra for raft foundations or to bridge foundations, and I'm potentially severely inconvenienced should this delay our project significantly.

Any advice as to how we should proceed with TW (deal directly initially or through our solicitors), or alternatively any thoughts as to what the likely solutions may look like (both in terms of build, additional costs incurred and future liability)?

I probably hold the record now for average words per post, so thanks in advance if you have read this far and can help!

Doozergirl

The rules changed on what was considered a public sewer back in 2011, I believe. It's more than likely that the previous vendor had no idea and considered them 'theirs'. The new legislation works in favour of the public as it is a simple transfer of any sewer that was previously private and shared between two or more houses before it hits the main sewers. In the past, only shared sewers belonging to houses built pre-1937 were adopted by the water companies.

Because your pipes were never built to be the responsibility of Thames Water, they are not mapped. During the building process of your new extensions, the building inspector needs to inspect your trenches, at which point he will see the pipes and request that they are built over correctly. You'll need the build over agreement to get your completion certificate.

Building over a small sewer like yours should be simple. Even if it was private, a builder should ask about drains and should treat it in the same way and your architect should have accounted for them when placing the design.

Before 2011, you'd have been the one forking out to lift that manhole and clear the drains. Now it's free. For anyone not building an extension, it's win/win. For you, it's swings and roundabouts. You'll need a buildover so that TW can safeguard their new responsibility.

Inconvenient, but not worth a fight over. I can see what you thought, but this is as new to TW as it is to you.

Dogbolter

Thanks Doozergirl for the quick response.

I understand that historically a sewer constructed for 4 properties may have be unknown to TW, but the fact that 5 new properties have been constructed and linked to said sewer about 7 years ago, along with the fact that TW have had to unblock this sewer on numerous occasions since (inc. after 1st October 2011 when ownership changed) means that I find it hard to believe that TW haven't updated their maps since.

You can't see that the sewer turns and runs diagonally across the area in question from a visual inspection of the manhole in our property - the sub-contractor based his informal statement of an inspection from the main sewer manhole on the main road outside our property, and this seems to be confirmed by the plan in the original deeds.

Should I not raise this then I believe that this would not necessarily be spotted by the building inspector - the sewer looks to be about 6 feet deep, which I understand is likely to be 3 feet deeper than any garage foundations.

Where would liability lie if the garage were constructed with building regs approval and TW approval only for subsequent problems to occur below the garage? If no sewers are mapped then build over agreements and manhole access wouldn't be required...

Finally, I guess there may be problems down the line for any prospective future purchaser should the sewer maps be updated subsequent to the garage build?

Thanks again.

Doozergirl

Anybody who shares a drain with their neighbours - let's face it, that's most of us, now has a public sewer on part of their land. There should be no issue with prospective purchasers because it isn't an issue.

I'm not quite sure what you want me to say when you suggest ignoring it? If something goes wrong underneath your garage, then mess and upheaval ensues, regardless of whether you get a buildover agreement.

If you don't have one, then there's a potential argument over who is responsible. If you do, it's TWs problem. Personally, I'd save myself potential hassle and be glad that they have to sort out the problems that come with having poo from 11 houses coming uder my back garden.

Anyone who owns a house really should know or research where the waste goes from their house. I don't see how trying to play one-up on TW helps you.

bigadaj

I'd agree it's a bit swings and roundabouts.

I would tend not to raise this as an issue and see how things pan out. Depending on the exact location of the foundations and the sewer relative to each other then it should be easy to span it with a little reinforcement and not a huge amount of cost. The problem might be the doth if the sewer as you'd normally run a 1in3 line beneath the new foundations to work out the stress distribution, the deeper the sewer the larger the span.

The problem once you've built is maintained e of replacement of teh sewer, TWs preference would be to dig out and replace but they won't be able to access this easily once you've built. There are alternatives such as micro tunnelling but they are expensive.

Dogbolter

Thanks both. I will indeed play nice with TW - it makes sense to minimise both long term cost and risk on both sides, unless of course delays and unplanned personal expense become too much...

Appreciate your thoughts and time.