Rats under decking – the facts and the fantasy

So general consensus is that we as humans like to have an area of hard standing just outside the back door and in the last 20 years or so the cheap fix to this need is a few slats of decking.

Because this has to be close to door level, these slats all sit on a suspended frame and therefore a cavity area is created beneath.

Bosh, you have somewhere to smoke, have a BBQ, drink alcohol and ponder on the point of it all.

But it’s the creation of this cavity area that causes the problem because rats love a cavity – they can’t really exist in life without one.

In comparison, a stone patio is a solid entity (generally) so there is nowhere for a rat to occupy but the cavity under a decked expanse is just the right height to create a snug sheltered nesting site for any members of the local rat population.

In addition, rats have learnt that these man-made cavity areas are great places to find food – people feed dogs on the top side, feed themselves & others, feed birds/fish and also have sheds often full of pet food and fishing bait in close proximity which again are easy to access.

The rat will always want to nest in a location that brings the best compromise between safety and access to food sources – i.e. the balance between the safest nest site and the shortest commute for food.

We call this the ‘McDonalds drive-through’ model and all rats will strive for it as its good for survival – (1) maximum calorie intake (2) in the safest place (3) with the least energy expenditure.

Decking in rear gardens tends to offer just that plus will also attract a tapas of insect life too again attracted by the dark, stable environment that lies beneath so plenty for rats to snack on inbetween any foraging missions.

That’s the more obvious set-up as to why rats like decking but there are some other issues that aren’t quite so obvious….

When decking is installed often the vertical components of the underlying frame are simply hammered into the ground.

Quite often drainage pipework (especially surface water systems) is surprisingly shallow and these posts can be hammered straight through a pipe top – this then allows rats in the pipework to burrow up to the surface beneath it.

In addition, often decking is built over other drainage aspects such as external gulleys, channel drainage etc. and again the protective grates can be dislodged or gnawed through allowing rats to come up from the connecting pipework and again occupy the void area below it.

But main cause of rats under decking?

Typically decking appears in our lives once we’ve built an extension – builders find it a quick and easy way to tart up a garden that’s otherwise been devastated by the foundation dig and build in general.

If the extension is a ‘build over’ (i.e. sits over the main waste run as would typically be for anything pre war) then the usual game is to decommission the original private connections and then run a new PVC system out to an external manhole before then feeding it back into the main run.

The new external manhole then sits under the decking out of sight.

When an extension is built over drainage in this manner, lintel bridges have to be constructed into the foundations to allow the building to sit over the pipework.

The typical scenario for this set-up is that the builders don’t properly cap the original connections when they decommission them so rats burrow out and enter the extension building fabric from the waste system that lies beneath.

Once within the building fabric of the extension, they then burrow out from the lintel bridge points and appear under the decking.

They will then continue to come and go from the extension building fabric both from the waste system and also from above ground via the lintel bridge burrows concealed beneath the decking.

At Pestology we believe that decking is like shell suits and in 20 years we’ll be laughing at it in the old family photos but till that day arrives there will still be a strong association with rat issues.

However the reason the rats are there is sometimes more sinister than you first envisage so if you are hearing noises in the extension fabric or the pets are behaving strangely then maybe its not just the decking the rats are occupying!

In which case call Pestology and engage a company that truly understands the full dynamic rats under decking can involve.