Extension built over drainage T-junctions - no access to manholes...

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A very brief history.
1970's detached house with domestic drains running along the side of the house.
Drain has 2 T-junctions into the original house to pick up the soil pipes.
2008 extension built (on piles) over the drain and the 2 manhole covers that access the T-junctions.

The architect specified that drain covers needed to be extended into the extension to allow access.

However, the council inspector visited during the build and said that it was fine to build over the manhole covers provided it was possible to rod the length of the extension (this was relayed by the builder but the works were approved on completion)

We have subsequently been plagued by rats gaining access to the extension walls & loft, via the void under the extension.

Since the straight section of the drain has been lined, the rats are accessing the void under the extension via one of the manhole covers or a crack in one of the 2 T's leading from the soil pipes in the main house.


1. Am I totally wearing this problem or do I have any recourse?

2. Either way, are the only 2 solutions available:
a) Rip up the extension floor and walls, repair drains and build access to manholes. This would be huge as the rooms & kitchen have tiled floors, underfloor heating and the layout was made around the fact that there were no manholes.
b) Dig down at the side of the house, go under the piling raft to access the manholes and pipes - if this was possible there are lots of different solutions available. But I expect Health & Safety issues would prevent this.

I have no doubt that the house could not be sold in its current state.

Any (constructive) advice or suggestions would be welcome.
Thanks
 
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First and foremost. Are you certain the rats are travelling through the sewers ? They can travel above ground as well as through underground routes. Do any of your heighbours have anything that would attract rats., chickens, food storage in sheds, waste materials in gardens etc etc. Rat colonies can grow in such places and when the colony is too large for the location they start emmigrating to nearby places that are warm.

Have you contacted the Rodent Control Officer in you local council ? They will often visit houses free of charge to advise on the best way to elimate the rodents.
 
Rats tend to nest outside of drains. The manholes may not be your problem.
 
I am 100% confident that the rat population is accessing my extension via the drains.

The void under the extension is probably a dry and warm place to build a nest (i.e. outside of the drain).
The rats have also nested in our loft previously - producing numbers of offspring.
All of the neighbouring gardens are very well tended and don't house any chickens, compost heaps etc

To reiterate my confidence in the origin of the rats, I offer this:
The exterior walls have plastic air vents that 'periscope' from the void under the extension up to the external air brick.
The rats have chewed away at these (where they vent into the void) to access the cavity wall and from there they gain access to the extension loft.
I have filled the cavity walls from the base of piled raft to just under the damp course with almost 2 feet of 20 mm gravel but they will tunnel up through that (I have laid metal and blocks atop of their tunnelling activities and this has been relatively successful)

The local council (Basildon) no longer have a Pest Control Officer - a victim of the cuts.
To be honest, I can catch rats (I've got quite good at it..), I am trying to tackle the root cause here.
 
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Have you had the drains CCTV surveyed to see if that shows anything up?

Hi,
Yes, the drains were surveyed with CCTV and a crack was found. This lead to the entire straight length of drainage being lined (i.e. that runs the length of the extension i.e. about 35 feet).
The operator actually captured rats on the video footage - something he said was extremely rare (I guess they usually get out of the way and hide)

The problem is that the 2 T's that lead of the straight length to the soil stacks, in the original house, cannot be surveyed - because the CCTV cannot get round corners - and even if it could, it would be impossible to put a liner in these pipes.

Thanks
Andy
 
Nothing is impossible, where there is a will there's a way. Need to check, on the CCTV did it show manholes? I'm just trying to ascertain if the laterals connect in manholes or on junctions, (i.e. no manholes). Secondly, the internal soil pipes, do you know if they are plastic?
 
Nothing is impossible, where there is a will there's a way. Need to check, on the CCTV did it show manholes? I'm just trying to ascertain if the laterals connect in manholes or on junctions, (i.e. no manholes). Secondly, the internal soil pipes, do you know if they are plastic?

There are 2 manholes concealed under the extension - both have T's that accept the soil pipes from the house. The soil pipes will be plastic, although the actual drainage pipes they connect to will be terracotta (or whatever is used).
I'm trying to attach a diagram which will be worth 1000 words :D
Give me a minute
 
Diagram...
I've had to take a photo of my PC to capture this... I was hoping to upload the Excel spreadsheet. But clicking on photo gives a reasonable image.
 

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With the soil pipes being plastic, I saw a glimmer of hope that the laterals may have been able to be relined from inside the property. (Easy to graft a repair back in on plastic.)

I'm afraid though if there is any doubt about the integrity of the chambers, you have little choice but to pull the floor up and expose them. The BCO at the time must have needed his head looking at, whilst access could be got to the soil pipes via access doors inside the building, I wouldn't want to open them and work from there if the laterals ever blocked. Bad enough doing it from an internal chamber.

Only other possible alternative I can see from here, is to lay new drains outside the footprint of the building and reroute the internal soil pipes to meet, then abandoning and sealing off the old system. No idea though if that's practical or even possible without seeing the job.
 
Only other possible alternative I can see from here, is to lay new drains outside the footprint of the building and reroute the internal soil pipes to meet, then abandoning and sealing off the old system. No idea though if that's practical or even possible without seeing the job.

This is my thinking.

One of the soil pipes only services an en-suite bathroom and I think this could be routed inside the house/extension to the other soil pipe.
That would mean connecting only one soil pipe up to the new drain system.
The big question is whether any contractor would be prepared (or allowed) to dig into the void under the piled extension to connect it all up?

If digging under the extension is not viable, eliminating one soil pipe would reduce the amount of work if the decision was made to dig up the floor.

I really appreciate your input and understand that you can't give a firm opinion without seeing the job.
To get a solution should I contact an architect, the council, a builder? Or all three!
 
I cant see anyone wanting (or being allowed to) basically tunnel under the building, its not something I think that's common practice, and probably too risky anyway. Your best bet is going to be looking at routing the soil pipes through the building, above ground, (i.e. under floors, or boxed in), and then piercing the shell to join a vertical stack on the external wall, connected to a new drain.

The abandoned pipework can be sealed off as required. I'd speak to a builder, see if the idea is possible firstly, and then take it from there. Building Control will need to approve any alterations to the drainage system, they might be happy to inspect what's in the ground before backfilling, so wont necessarily need a drawing.
 
Thanks very much - I really appreciate your help & support.

I will, more than likely, take the course of action you suggest.
I will take the precaution of an additional opinion on the source of the rats before proceeding - as the outlay for that will be pennies compared to the potential work & upheaval involved in moving drains etc.

Regards
Andy
 
Fit some grills inside the accesible manhole to isolate your colony. You might have to hose it out every week as the number twos might block it. At your rodding hole push down rat poison. The stuff I bought from Wilkos (their own brand) both mice and rats gobble it up like a kid eats sweets. Hopefully after a month or so the little b*gg*rs will all be dead. Push the poison through the air vents into your under floor void. Could be that the vents should be remade out of metal or at least putting a metal mesh over them. Removing them from the outside would give you access to the under floor void without lifting the internal flooring. I see that you filled some of the void with with gravel, it might be a discussion point to flood it with a cement/water grout to provide a proper hard seal. I think that the gravel only gets in the way of seeing the rats tunnels and has proven to have a limited effect.
I note that you have no stack pipes on this dead end of a sewer run.
Frank
 
Thanks Frank - all good points. To which I have answers to all of... :D
At the end of the day, killing the rats or preventing them from accessing the cavity walls & loft is not the end of the story.
I need to keep them in the drains and out of the void under the extension. I doubt the house could be sold as it stands.
We have just started to engage the local council - as it would appear that no inspection or completion documents from from Building Regs people were provided.
Even though the original plans were approved by the council - I'm started to think this could run & run...
Regards
Andy


Fit some grills inside the accesible manhole to isolate your colony. You might have to hose it out every week as the number twos might block it.
I understand & like the theory but in a house with a number of children/women, who can block a toilet s-bend with toilet paper (I kid you not), I suspect that hosing it out the accessible manhole would be a daily job!

At your rodding hole push down rat poison. The stuff I bought from Wilkos (their own brand) both mice and rats gobble it up like a kid eats sweets. Hopefully after a month or so the little b*gg*rs will all be dead. Push the poison through the air vents into your under floor void.
Having suffered a least 6 rats decaying in inaccessible parts of the loft or within the cavity walls, poison is a no-go for me. The smell lasts for the weeks and at some point you get a swarm of bluebottles. How my wife has put up with this is beyond comprehension!

Could be that the vents should be remade out of metal or at least putting a metal mesh over them.
These vents are plastic periscope vents - i.e. a vent into the void is connected to a vent in the external wall by a vertical rectangular plastic box about 18"-24" long. The rats have simply chewed through the vent and box where it exits into the void - gaining access to the cavity wall. One idea of mine was to drop concrete blocks (i.e. something like sawn off fence posts) either side of the vents and cement them in place. This would stop the rats exiting the void.

Removing them from the outside would give you access to the under floor void without lifting the internal flooring. I see that you filled some of the void with with gravel, it might be a discussion point to flood it with a cement/water grout to provide a proper hard seal. I think that the gravel only gets in the way of seeing the rats tunnels and has proven to have a limited effect.
Spot on. The gravel did slow them down - I could hear them burrowing through it. The main benefit of it was that it identified which air vent they were using to access the cavity wall from - I was then able to replace the gravel they had pushed out and lay brick and a metal grill over those specific areas. This has stopped them for the time being.
Filling the bottom of the cavity wall with concrete was considered but I was concerned about the risk of damp etc. I thought gravel was a good half way house as it could be removed if needs be and a certain amount of ventilation was possible.

I note that you have no stack pipes on this dead end of a sewer run.
That's right that end of the drain was a dead end which was angled upwards to accept a rodding eye.
 

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