A large proportion of rat infestations are caused by defects/erosion in sewer systems such as collapsed drains, damaged pipes and uncapped/disused pipework. Sewers provide ideal conditions for rats; they are cool in the summer and warm in the winter, as well as providing shelter and an abundance of food.
A structurally sound sewer system provides few opportunities for rats to gain access to connected properties, however a large proportion of modern day systems are not perfectly sound and rats can find their way to the surface through defects in the system. There is strong evidence linking more than 50% of surface infestations to drainage defects and this figure is likely to be higher in more urban areas.
Exterminating rats from sewers is arguably more difficult than controlling them at ground level. In order to be successful, it is imperative that we utilise what is known about rat bionomics and behaviour traits. One of the first questions people ask themselves when faced with an infestation is "why have I suddenly got rats? I've never had them before". A lesser-known fact about rats is that they often migrate to different areas for a number of reasons. This could be because of overpopulation and food shortages, flooding or simply because of a disturbance that makes them feel uncomfortable. Rats are extremely intelligent creatures and will do what it takes to survive. They are wary of danger and have neophobic tendencies which is why it can take a substantial amount of time to eradicate them from any given area.
Rats become a hazard in premises when they live in the drains and make visits to the surface to forage for food. They cleverly negotiate badly designed watertraps and when living in sewers, have the ability to cause structural damage as they make holes in surrounding earth and eventually gain access via faulty joints or perished brickwork. Complete elimination from sewers is often unattainable, however it's important to put control in place to avoid your property being overrun. It is also worth remembering that you are at a high risk of rat borne diseases such as leptospirosis so swift control is imperative.
Sewer systems vary in structure and layout and are generally classified into "soil" sewers and "storm-water" sewers. In some areas, there are separate soil and stormwater sewers but in others, there are combined or partially combined systems where the surface drains discharge into the soil sewers allowing greater freedom of movement for rats. Older sewer systems are generally made from glazed stone-ware such as fireclay, but can also be concrete or cast iron. Rats can manoeuvre these systems with ease as the bricks protrude at different levels, giving them ample opportunities to scramble their way to the surface. Modern drains and sewers are far more superior as their surfaces are much smoother which makes it much more difficult for rodents to climb. Unfortunately, a large proportion of today's sewer systems are in need of updating but work is delayed due to the mammoth effort required. This type of renovation project is a costly task and councils simply don't have the budget to carry out such works.
When it comes to preventing rats from entering your property via your drains, there are a number of steps that can be taken. A large proportion of people simply think that laying poison will sort the problem out but in reality, things are far more complicated! Rats have access to an abundance of food and will generally consume bait as a 'last resort/ if food is scarce. This isn't to say that bait is not effective, it simply means that it should not be solely relied on as a method of control. Rodenticide must be used responsibly to prevent problems such as resistance and secondary poisoning.
Further information can be found at:
A drain survey that uses a camera is the best way to ascertain if you have a defect in your drainage system. The surveyor inserts a probe into your drain and can identify issues such as disused pipes, cracks or collapsed pipes. An average drain survey costs around €280 plus VAT, but it's well worth the outlay as it allows you to tackle the problem at the source.
Another popular method of control is to install a drain guard, also known as a rat blocker. These robust devices prevent rats moving towards your property by blocking their access, like a one-way valve. The drain can still flow as normal and the function is not compromised in any way. This method is by far one of the most popular as it it is a simple yet highly effective method of control.
The best way of determining whether your rat infestation is the result of a faulty drainage system is to contact the professionals. Rodent control technicians have the knowledge and expertise and will find the most cost-effective solution for your rodent problem.