What Are Rat Flaps, How Do They Work & Do I Need One Fitted?

By Exterminate Pest Control

If rats keep turning up under your kitchen floor, behind the toilet or inside a wall, the route into your home could be underground. Rats can travel from a public sewer into the drain serving your property and leave the pipe through a broken joint or an open connection. A rat flap can block rats travelling up a suitable drain towards your house. Whether you need one depends on where the rats are getting in.

What Is a Rat Flap?

A rat flap, also called a rat blocker or non-return rat valve, is a one-way device fitted inside a drainage pipe. It allows wastewater to flow away from your property while blocking rats attempting to travel back up the pipe from the sewer side. Many designs use a hinged stainless-steel flap.

How Does a Rat Flap Work?

The flap opens in the direction of wastewater flow. When you flush the toilet or empty the sink, wastewater pushes the flap open and passes through. Once the flow subsides, the flap closes. A rat approaching from the opposite direction meets a barrier that is designed to resist being pushed open from that side.

A flap only protects the route it is fitted to. If your property has two separate connections, a shared drain or an old branch that bypasses the device, rats may still have another way in. This is why the layout of the drains matters as much as the size of the pipe. 

Do I Need a Rat Flap?

A rat flap is worth considering if an inspection points to rats travelling up the foul drain towards your property. A rat in the kitchen or attic tells you where it ended up. An inspection helps establish how it got there.

What you’re seeing

What to check first

Rats keep returning under the floor after treatment

Survey the drains for a route from the sewer and check for damaged or open pipework beneath the property.

Burrows keep appearing near an inspection chamber

Check the chamber, nearby joints and surrounding ground for a connection between the drain and the burrow.

Rat activity started after an extension or bathroom renovation

Check whether old drainage branches were properly sealed and whether working pipes were damaged.

Rats are getting in through an obvious gap at a door, vent or soffit

Address the identified opening. A drain flap only helps if there is also a route through the drains.

Several adjoining properties have recurring rat activity

Check whether the homes share a drain and which branches would actually be protected by a flap.

Irish rodent-control guidance identifies defective drains and redundant pipework as potential entry routes. The HSE also highlights openings around waste pipes, vents and other services as points to check when proofing buildings.

Will a Rat Flap Fix a Broken Drain?

A broken drain needs to be repaired. A flap can block rats coming from the sewer side, but a cracked pipe, displaced joint or uncapped branch can still allow rats to move between the drain and the surrounding soil. Rats already inside the property or on the house side of the flap also need to be dealt with. Depending on what the inspection finds, the job may involve drain repairs, rat treatment and proofing, with a flap added where it protects a confirmed route. 

Where Should a Rat Flap Be Fitted?

A rat flap is often installed at a suitable pipe opening in an accessible inspection chamber. The installer needs to identify which pipe serves the property, confirm the direction of flow and select a device suited to the pipe’s diameter and condition. The flap should remain accessible so it can be checked and cleared if debris interferes with its movement. On shared drainage, the location also determines which properties and branches the flap protects.

Can a Rat Flap Block My Drain?

A flap needs to open freely. Debris can interfere with its movement, and an unsuitable device or installation location can restrict the flow. If the drain already backs up or clears slowly, have the cause investigated before fitting a flap. Ask the installer how the device can be accessed for inspection and maintenance.

Book a Rat Drain Inspection With Exterminate Pest Control

If you hear rats beneath the floor, notice burrows near a drain cover or keep finding fresh droppings after treatment, tell us where the activity is happening and whether the property has had recent building or plumbing work. Contact Exterminate Pest Control on 0852635994 to arrange an inspection and find out whether a rat flap is suitable for your property. Exterminate.ie