Understanding inspection pit layout / rat issue.

[trebarwith33]

We've started hearing rats under floors, in walls and in the loft. Not every day, but after previous issues with our last house, hearing them once is enough!
It's a semi detached converted bungalow, I've had a good look around outside and no signs of any entry points. Air bricks, gully pots and around down pipes all look fine.
I put a camera in the inspection pit to get an idea of what is going on and confirmed there are rats down there (obviously!) but trying to understand the layout and how they might be getting in from here. The pit is about 2m deep, so there's another rung and about 50cm of bricks above this image to get to the surface.

Pipe A leads to downstairs bathroom (directly to toilet under floorboards and then the bath & sink run via a waste pipe that drains into a gully pot outside.
From observing the rats, Pipe A also leads to Pipe A1. It takes them about 10 seconds so must be a short run. Whereas A to the toilet/gully pot is about 5m and about a 2m difference in height so I assume A1 is some kind of vent that rather than running all the way to the house?
Pipe B leads to a soil stack that the upstairs toilet, shower and sink feed into. When rats go in here, they come out within a couple of seconds. I assume because the soil stack is very close to the pit that it's a vertical drop. I've never seen a rat go into B and come out B1, but I have seen them go from A1 to B1, but return quickly and go back down to A. Pointing a camera into A1 and B1 it seems they both drop down quite quickly.
Pipe C leads to a gully pot outside the kitchen (sink, dishwasher, washing machine). Similar to B, rats occasionally go in put come out in a second or 2. Above Pipe C is another pipe not shown (C1), same height as A1 and B1.

From watching their movements, they mostly run between the main sewer (right, no houses this side) and upstream (left, to about 8 other houses, the first being our attached neighbours). They mostly mooch about in this pit and occasionally go up pipe A to A1, B1 etc, but they're only ever in there for a few minutes tops. No sightings on a camera in the loft, or noises we've heard in the house coincide with any activity on any pipe shown so I've come to the conclusion they're probably not accessing via our pipes at least as this is the entirety of our plumbing in this one pit. (Gutters and downpipes lead to a soakaway).

I guess my main questions are:
- What are pipes A1, B1, C1? They are completely dry, no signs of anything coming out of there (no old stains, dripping etc).
- Am I likely correct in my assumption the rats are probably accessing our house via the neighbours side (either via sewer, or above ground somewhere)? would a 1950s bungalow share a cavity? Would there typically be air flow/gaps between the 2 houses under the suspended floors?


Thanks for reading!

 

[Hugh Jaleak]

Given the depth of the chamber, I would hazard a guess the incoming drains are connected via a 'Backdrop', that is where the incoming drain runs at a higher level, before dropping to enter the chamber at the invert (bottom channel) level. The higher pipe then continues horizontally to the chamber, to provide access upstream from the chamber for rodding in the event of a blockage. What you can see on the camera going in the upper outlets, is the drop pipe going down to to enter the chamber at the bottom.

The rats are pretty adept at finding daylight and this a convenient entrance/exit from the drainage system to emerge to find food etc. They are pretty good climbers, so I would be cautious about keeping a Lid down on your ground floor WC, (the water in the pan wont stop them!)

Only takes a small gap for Rodents to squeeze through, they could well be getting access via a broken pipe in the Neighbouring property, and then getting into the Cavity.

I would be seeking the advice of a Professional Pest Control company (or the Local Council) at this stage, they need dealing with before things get out of hand.