Why Are There Cockroaches in My Spanish Apartment?
The real reasons cockroaches appear in Spanish apartments — shared drainage, building age, climate factors — and how to stop them coming back.
By James Thornton
You moved into your Spanish apartment. You cleaned it thoroughly. You don’t leave food out. And yet — cockroaches. You’ve found one in the bathroom at 2am, another scurrying under the kitchen sink. Maybe your neighbours say they have the same problem. Maybe they don’t, which makes you wonder what you’re doing wrong.
The answer, almost certainly, is nothing.
Why Is It the Building and Not You?
The number one reason cockroaches appear in Spanish apartments has nothing to do with how you live. It’s how the building is plumbed.
Spanish apartment buildings connect every unit to a shared drainage stack called a bajante. Your bathroom drains, your kitchen waste pipe, and your neighbours’ — above, below, and beside you — all feed into this communal vertical pipe, which empties into the municipal sewer.
The sewer system beneath any Spanish city supports enormous cockroach populations. These cockroaches — primarily American cockroaches — travel through the pipes looking for food and harbourage. When they reach a dry P-trap or an unsealed pipe entry, they enter the nearest apartment.
This means your neighbour’s dry guest bathroom drain can be the reason you find a cockroach in your kitchen.
The Five Entry Routes
In a typical Spanish apartment, cockroaches have multiple ways in:
-
Floor drains with dry P-traps. Every bathroom has a floor drain (desagüe de suelo). The U-shaped pipe beneath it holds water that creates a seal. When that water evaporates — it takes just 2–3 weeks in summer — the seal breaks and the sewer is open.
-
Pipe gaps through walls. Where waste pipes, water pipes, and gas lines pass through walls and floors, there are almost always small gaps around them. Cockroaches can squeeze through remarkably tight spaces — a gap of just 3mm is enough for a German cockroach.
-
The communal drainage stack. If the bajante has cracked joints or deteriorated seals (common in buildings from the 1960s–80s construction boom), cockroaches exit into wall cavities and spread horizontally through the building fabric.
-
Open windows and balcony doors. In summer, flying American cockroaches are attracted to lights in the evening. Upper floors aren’t safe — they can fly to the third or fourth floor.
-
Cardboard and deliveries. German cockroaches — the small indoor species — arrive via cardboard boxes, grocery deliveries, and second-hand furniture. They don’t come from the sewer; they hitchhike.
Which Species Tells You What’s Going On?
The cockroach you’ve found reveals the entry route:
Large (3–5cm), reddish-brown → American cockroach. Came from the sewer through a drain or pipe gap. Usually a lone individual, not an indoor colony. Solution: seal the drains.
Small (1–1.5cm), light brown → German cockroach. This one breeds indoors. It didn’t come from the sewer — it arrived via cardboard, shared walls, or was already here when you moved in. Finding several means you have a colony. Solution: gel bait treatment.
Medium, very dark brown/black → Oriental cockroach. Prefers damp areas — ground-floor properties, basements, garages. Enters through drains and exterior gaps.
Identification matters because it determines your response. An American cockroach from the drain needs a drain cover. A German cockroach colony needs bait.
Why Is Your Apartment Affected Specifically?
Within the same building, some apartments get more cockroaches than others. The reasons are usually:
- Lower floors are closer to the sewer and ground-level entry points
- Apartments with more unused drains (guest bathrooms, utility rooms) have more dry P-traps
- Corner and end units may have more exterior pipe penetrations
- Units above the building’s sótano (basement garage) are directly above open sewer connections
- Apartments facing trees or gardens get more flying cockroaches in summer
None of these factors relate to cleanliness. They’re structural.
Talk to Your Vecinos
Ask your neighbours (vecinos) whether they see cockroaches too. If multiple apartments in your building have the problem, it’s a communal infrastructure issue that should be raised at the junta de propietarios (owners’ meeting). The comunidad can hire a pest control company to treat common areas and inspect the drainage stack — and under Spanish property law, this cost is shared among all owners.
Get our apartment pest-proofing checklist
Every entry point to check and seal in a Spanish apartment. Room-by-room guide with product recommendations for drain covers, sealant, and screens.
No spam. Unsubscribe anytime.
How Do You Stop Cockroaches in Your Apartment?
The protocol for a Spanish apartment is straightforward and costs under €50 in materials:
Week 1 — Block the routes:
- Fit stainless steel mesh drain covers on every floor drain (1–2mm mesh)
- Run water through every unused drain to refill P-traps
- Seal gaps around all pipes with bathroom-grade silicone
- Install window screens on openings you use in the evening
Week 2 — Monitor:
- Place sticky monitoring traps behind the fridge, under the bathroom sink, and near floor drains
- Do the tape test on drains to confirm they’re sealed
Ongoing:
- Run water through unused drains weekly
- Break down cardboard deliveries immediately and take them outside
- Replace silicone seals annually
If you’re seeing German cockroaches — the small indoor species — add gel bait behind the fridge, under the sink, and inside kitchen cabinets. Gel bait works through secondary kill, reaching cockroaches hiding in cracks you can’t access.
The Bottom Line
Cockroaches in your Spanish apartment are not a judgement on how you live. They’re a predictable consequence of Mediterranean climate, shared building drainage, and the specific way Spanish apartments are plumbed. Every expat who moves to coastal Spain has this moment of shock — and every one of them learns that it’s manageable.
Seal the drains. Seal the pipe gaps. Screen the windows. The cockroaches are still in the sewer — they just can’t get into your home. For the full treatment protocol, see our complete cockroach guide.
Written by James Thornton
Founder & Lead Writer
British expat living in Málaga since 2019. Researched 200+ pest control cases across 16 Spanish regions.
Reviewed by Carlos Ruiz Martín
ROESBA-certified (Spain's Official Pest Control Registry). DDD specialist. Member of ANECPLA.
You Might Also Like
Cockroaches Coming Up Through Drains
Why cockroaches enter Spanish homes through drains, how the sewer system works, and permanent solutions.
Cockroaches in Rental Property Spain
Who pays for pest control in a Spanish rental — your rights, your landlord's obligations, and how to handle it.
The Complete Guide to Cockroaches in Spain
Everything you need to know about cockroaches in Spain – species, biology, and the most effective treatments available.