If you have just moved into a Dutch house and you hear scratching under the floorboards at night, there is a good chance you are dealing with rats in the crawl space. Almost every older Dutch home has one: a shallow void of fifty centimetres or so between the ground and the ground floor, known as the crawl space (kruipruimte). It is dark, it is undisturbed, and in most of the country it is damp. For a brown rat, that is close to ideal.
This article explains why the crawl space is such a magnet, how to tell rats apart from mice down there, and what a certified technician actually does when they open the hatch.
Why the Dutch crawl space attracts rats
The Netherlands sits low, and the groundwater sits high. In much of the west of the country the crawl space is permanently humid and sometimes holds a layer of standing water. That does not bother a brown rat, which swims well and drinks readily.
Three things come together down there:
- Shelter. Nobody goes into a crawl space for months or years at a time. Nests are not disturbed.
- Water. Condensation, a leaking pipe or groundwater is enough.
- Routes in. The crawl space is connected to the outside world by ventilation gratings, and often to the sewer by old or damaged drainage.
The last point is the one most people miss. A crawl space is deliberately ventilated through small gratings in the outside wall at pavement level. Those gratings are supposed to keep rodents out, but on houses built before the war they are frequently rusted, cracked or missing entirely. A young rat needs a gap of about two and a half centimetres.
Signs of rats in the crawl space
You will almost never see the animals themselves. What you notice instead:
- Noise at night. Scratching, gnawing or a heavy scurrying sound from under the ground floor, usually between dusk and the small hours. Rats are noticeably louder than mice.
- A sweet, musky smell near the hatch, near floor sockets or where pipes come up through the floor.
- Droppings near the hatch: rat droppings are fifteen to twenty millimetres, dark and spindle shaped, while mouse droppings are the size of a grain of rice.
- Gnaw damage to cabling, insulation or plastic pipework, sometimes noticed first as a tripped circuit.
- Greasy smear marks along a wall or a pipe run, where the same route is used night after night.
If the sounds come from the ceiling or between floors rather than from below, you are more likely to be hearing mice or, in some areas, a marten. The location of the noise is genuinely useful information, so make a note of it before anyone comes out.
Why treating the crawl space is not a do-it-yourself job
Two reasons, one legal and one practical.
Since 2023, rodenticide in the Netherlands may only be used by professionals who hold the relevant certification, and only inside a documented Integrated Pest Management approach. Buying poison as a private individual is no longer an option, and glue traps are best left alone regardless of what is sold online.
The practical reason is that poison would be the wrong first move anyway. A rat that dies in a crawl space you cannot reach is a problem, not a solution. Professional rat control starts by working out how the animals are getting in and what is keeping them there, because a crawl space that stays open simply refills a few weeks later.
What a technician does when the hatch comes up
A first visit is an inspection, and it is free. Expect roughly this:
- The hatch is opened and the void is inspected properly, with light, over its full depth rather than from the edge.
- Droppings, runs, nesting material and smear marks are mapped, which shows how long the activity has been going on and roughly how many animals are involved.
- Ventilation gratings, pipe penetrations, the sewer connection and the perimeter are checked from the outside.
- You get a written plan and a fixed price before anything is done.
Treatment itself is usually a combination of sealing the ways in and placing monitored control points, followed by a check visit to confirm the activity has actually stopped rather than moved.
Keeping them out afterwards
Once a crawl space is clear, the work that keeps it clear is mostly proofing and prevention: replacing damaged ventilation gratings with rodent-proof ones, closing gaps around pipes and cables where they pass through the foundation, and having the drainage checked if there is any sign that the sewer is the route in.
Outside, the same logic applies as anywhere: no open food waste, no spilled birdseed, no dense cover growing directly against the foundation wall. A rat that finds nothing to eat within a few metres of your wall has far less reason to test your gratings.
Frequently asked questions
How do I know whether it is rats or mice under my floor?
Go by size and sound. Rats are heavy enough that you hear distinct scurrying and dragging, usually at night and often in bursts; mice sound lighter and faster. Droppings settle it: rat droppings are fifteen to twenty millimetres long, mouse droppings about five. If you find droppings near the crawl space hatch, photograph them next to a coin before anyone visits.
Is the crawl space my landlord's responsibility or mine?
In a rented home, rodents in the structure of the building are normally something you report to your landlord or housing association, because the crawl space, the foundation and the drainage are part of the building rather than your household. Report it in writing and keep a copy. If the infestation is clearly linked to how the home is being used, the picture can be different, so describe what you have observed rather than arguing the point.
Can I just block the ventilation gratings myself?
No, and it is worth being clear about why. Those gratings are there to keep the crawl space ventilated; closing them off raises the humidity underneath your floor and creates a damp problem in place of a rodent one. They should be replaced with rodent-proof gratings that still let air through, not sealed.