Rats In The Sewers In Ireland & How Rats Get Into Your House

By Exterminate Pest Control

You hear scratching under the kitchen floor. A few nights later, it’s in the wall upstairs. You’ve checked the doors, windows and air bricks and found no obvious gap. Could the rats be coming from the drains?

Yes. A rat can travel from a public sewer into a drain serving your home, squeeze out through a broken joint and burrow towards the foundations. It can also climb a vertical soil pipe and emerge near the roof. Where you hear the scratching may be several metres from where the rat first entered the building.

1. Broken Drains Give Rats a Route Under Your House

The foul drain carries wastewater from your property towards the public sewer. A cracked pipe, displaced joint or open branch can give a rat a way out of the drain and into the surrounding ground. If that defect is beneath an extension, kitchen or utility room, the rat may already be under the building before it leaves the pipe. From there, gaps around service pipes or openings into a wall cavity can give it a route indoors.

Old drains left behind after building work are worth checking. When a toilet is moved or an extension is built, a redundant branch can remain connected to the working drain. If its end was left open or the cap failed, it can provide a sheltered route into the property. The HSE’s guidance for the construction industry specifically addresses sealing junctions where disused pipes meet working drains.

2. Rats Can Tunnel From a Damaged Sewer Towards the Foundations

Brown rats are burrowing animals. Where a sewer or drain breaks, they can move into cavities outside the pipe and tunnel through surrounding soil. A burrow may lead to the surface beside a patio, an inspection chamber or an extension. It may also connect with an existing void under a floor or an opening where a service enters the house.

If a hole beside the same wall repeatedly reopens, or rats keep appearing near a chamber despite treatment, the drain is worth investigating. Burrows can also start at the surface, so checking how the hole lines up with the drain route and inspecting the pipework can help establish where the rats are travelling.

3. Can Rats Climb Wastewater Pipes All the Way to the Roof?

Yes. Rats can climb inside a vertical soil stack, the pipe that carries toilet waste down towards the foul drain. Some stacks continue upwards to a vent above the roof. A rat climbing the stack can escape through a defective joint or open connection along the way. If it emerges at roof level, it can look for a separate opening into the attic, such as a damaged soffit or a gap at the eaves.

The distinction matters when you’re tracing the route. The soil stack is connected to the foul drainage system. A gutter downpipe usually carries rainwater and can give rats an exterior climbing route where they can get a grip or use nearby brickwork, ivy or brackets. If you hear rats in the attic, check both the roofline and the vertical service routes below. Keep plumbing vents clear and have any suspected defect assessed before making changes.

4. Other Ways Rats Can Get Into Irish Homes

If you suspect rats are coming from the sewers, check these routes alongside the main drain and soil stack:

Possible route

What to investigate

Shared drains between neighbouring properties

A defect can sit on a shared section serving several houses, away from the room where you hear activity.

Inspection chambers

Damaged chamber walls, displaced covers or gaps where pipes enter the chamber can connect drains with surrounding soil or the surface.

Openings around waste pipes and other services

A rat may travel around a pipe through the gap in the wall or floor. Check behind kitchen units, washing machines and boxed-in plumbing.

Old gullies and abandoned connections

Look for unused branches after bathroom relocations, extensions or changes to an outdoor utility area.

Toilet connections

A rat can sometimes swim through a toilet’s water trap. If the activity is behind the toilet, also check the waste connection and surrounding pipe openings.

Above-ground routes

Ivy, rough walls and overhanging branches can help rats reach damaged soffits, roof gaps or other upper-level openings.

The HSE and Irish rodent-control guidance identify defective drainage, redundant pipes and openings around services as routes worth checking. Irish pest-control guidance also documents climbing and toilet access as possibilities.

How Many Rats Are There in Ireland?

There is no verified national rat count in the published sources. The Irish Times reported an estimate of about 10 million rats nationally, including about 4 million in Dublin, while noting that the total cannot be quantified. Those are rough estimates of the overall rat population. The number living specifically in Irish sewers is unknown.

The same report recorded 16,921 HSE pest-control callouts in Dublin in 2022 and 16,223 in 2023. Callouts show demand for the service. One callout can involve multiple rats, a repeat visit or activity unrelated to a sewer defect, so the figures cannot tell us how many rats were present or how they entered.

How Old Are Ireland’s Sewer Networks?

Uisce Éireann estimates that Ireland has around 26,000 km of public sewers and about 2,200 public wastewater pumping stations. The network was built and extended over many generations, so its age varies by location.

Dublin gives a sense of that history. The Rathmines and Pembroke main drainage scheme was completed in 1881, and the National Archives dates the completion of Dublin’s first major city drainage system to 1906. These are milestones for schemes built more than a century ago. The condition and age of the particular pipe serving your house depend on when it was laid, altered or replaced. A CCTV drain survey can help establish its present condition.

How Can You Tell If Rats Are Coming From Your Drains?

Start by noting where you hear the rats, where you find droppings and whether activity returns to the same spot after treatment. Scratching beneath a floor near an old extension, repeated burrowing beside an inspection chamber or activity in the boxing around a soil stack can help narrow down which parts of the property to inspect.

A CCTV rat drain survey can help locate fractures, displaced joints and open branches in accessible pipework. An inspection of the building can then look for the connection between the drainage defect and the indoor activity. Where a defect is found, the solution may involve repairing the pipe, sealing a redundant branch or proofing an opening around a service. A properly selected rat flap, also called a non-return rat valve, may help prevent rats travelling upstream through a suitable drain. Broken pipework still needs repair, and existing rat activity still needs treatment.

If the defect appears to be in a public foul sewer, contact Uisce Éireann. Where a private drain serves several properties, responsibility can be shared among the connected property owners. Establishing which section is affected helps get the repair to the right people. 

Book a Rat Inspection With Exterminate Pest Control

If rats keep returning under the floor, inside a wall or up in the attic, tell us where you hear them and whether the property has had an extension, bathroom relocation or recent drainage work. That information gives us a starting point for tracing the route.

Contact Exterminate Pest Control on 0852635994 to arrange a rat inspection or rat drain survey. Exterminate.ie