When you walk through an apartment, you naturally focus on what's visible: the renovation, the layout, the view, whether the taps look clean. But the defects that end up bothering you most after moving in are usually the ones no 20-minute viewing could ever catch. They only show up in daily use — during a heatwave, when the shower barely has enough flow to rinse off, or when two people want to shower at once. Here are seven that HouseDoctor inspectors run into again and again on Spanish homes.
Water Flow Too Weak to Shower Comfortably — or That Collapses When Two Taps Run at Once
On a viewing, someone turns on the shower for a few seconds and the water looks fine. But two different problems can hide behind that impression. Flow rate — how many litres per minute actually reach the shower head — is a different thing from pressure, and a weak flow can feel like standing under a garden hose even when the pressure gauge reads normal. Separately, the kitchen tap can run fine and the shower can run fine on their own, but open both at the same time — or run the washing machine while someone's showering — and pressure drops sharply at both fixtures.
Why it happens. Undersized supply pipes, a water heater that can't deliver enough flow at the set temperature, scale build-up inside old galvanised pipework, or a flow restrictor left in place from a water-saving fitting can all cap how much water actually reaches a fixture, regardless of mains pressure. A pressure collapse under simultaneous demand usually points elsewhere — to the condition of the building's main riser or a booster pump that's poorly matched to demand. During a viewing, agents typically demonstrate one tap at a time, so both problems stay hidden.
Why it matters. A weak flow makes rinsing shampoo or shaving gel take twice as long and turns a quick shower into a daily frustration; a pressure collapse means water that's scalding one moment and barely a trickle the next whenever someone else opens a tap or runs the washing machine — tolerable once, genuinely wearing every single day. Both are often blamed on "low water pressure" when the real fix is different — and often far more involved than it sounds. Cleaning or upgrading a water heater can seem like a minor inconvenience, but the actual fix is sometimes tearing into a wall to rip out old pipework that's been hidden inside it for decades and replacing it with new pipes of a bigger diameter, or revisiting the building's riser or booster pump entirely.
How it's checked. An inspector measures actual flow rate in litres per minute at the shower head and other fixtures, rather than relying on how forceful the stream feels, and separately opens several fixtures at once across the property to measure the pressure drop with a gauge — rather than testing a single tap in isolation, the way a viewing typically does.
Shower Drainage That Can't Keep Up, Leaving Water Pooling in the Tray
Water runs, disappears down the drain, and everything looks normal for the thirty seconds anyone watches on a viewing. But run a full shower for five minutes and in some bathrooms the water can't drain as fast as it arrives, so it creeps up around your ankles by the time you're done.
Why it happens. Common causes are a drain pipe with too shallow a slope, a P-trap or the horizontal run beneath the shower tray that's too narrow or partially blocked with old sealant and hair, or a shower tray installed slightly out of level so water pools in one corner instead of running straight to the drain.
Why it matters. Standing water on a shower floor isn't just unpleasant — it slows down every shower, encourages mould and unpleasant smells around the drain, and can eventually work its way under the tray or through grout lines into the floor below, especially in older buildings without a fully tanked wet room.
How it's checked. An inspector runs water continuously for several minutes and times how quickly the tray clears, checks the tray for level with a spirit level, and inspects the drain and accessible pipework for slope, blockages and signs of past leaks.
Heating That Can't Actually Keep the Place Warm in Winter
The radiators come on, the thermostat display lights up — and during a five-minute viewing on a mild day, that's as far as anyone tests it. Whether the system can actually hold a comfortable temperature through a cold snap in January is a completely different question.
Why it happens. Common culprits include electric radiators or a heat pump sized for a smaller original layout, a boiler that's undersized or ageing and losing efficiency, radiators that were never rebalanced after a renovation, or simply a home with poor insulation and single glazing that loses heat faster than the installed system can replace it.
Why it matters. In a genuinely cold spell, an undersized or inefficient system runs at maximum output around the clock without ever quite reaching a comfortable temperature, which means high electricity or gas bills for a home that still feels cold — and buyers coming from colder climates are often surprised how poorly some Spanish homes, especially older ones, are built to retain heat.
How it's checked. An inspector assesses the installed heating capacity against the property's size, insulation and glazing, checks that radiators or units reach and hold their set temperature, and looks for signs — cold spots, uneven heat distribution, condensation — that point to an underlying insulation or sizing problem rather than a simple thermostat setting.
An Air Conditioning Unit That's Too Small for the Room
On a viewing, someone switches the AC on, cold air comes out, and that's usually enough to tick the box. But the right unit size (measured in BTU or kW) depends on the room's floor area, ceiling height and glazing — not on how it feels for two minutes.
Why it happens. The unit was often sized for an earlier layout, and after two rooms were knocked into one, or the windows were upgraded, the actual cooling load changed. It's also common for a previous owner to have installed a cheaper, undersized unit to save money upfront.
Why it matters. In peak summer, an undersized unit runs almost continuously, the compressor wears out faster, and electricity bills climb — all while the room never quite reaches a comfortable temperature.
How it's checked. An inspector compares the installed unit's rated capacity against the room's floor area, ceiling height and sun exposure, and measures the actual temperature drop and how long the unit takes to reach the set point.
Missing or Undersized Extraction and Ventilation
The kitchen extractor grille is there, the windows look airtight — everything seems fine at a glance. But if the grille isn't properly connected to a working duct, or it feeds into a shared vertical shaft with no mechanical draw, and the windows have no trickle vents, the apartment simply doesn't get enough air exchange.
Why it happens. In older buildings, ventilation ducts are often shared between several flats and lose draw over time. Modern renovations with sealed PVC windows, installed for energy efficiency, frequently overlook the fresh-air intake that extraction actually depends on.
Why it matters. The effects build up gradually: cooking smells linger for hours, a greasy film settles on kitchen cabinets, the flat feels stuffy even in winter, and condensation forms on the glass. Left unaddressed, poor ventilation is exactly the condition that leads to damp and mould.
How it's checked. An inspector measures actual airflow at the extractor with an anemometer — not just whether the switch turns it on — and traces the duct route and the fresh-air supply into the room.
Poor Sound Insulation: Footsteps, Pipes and Street Noise Through the Walls and Windows
A viewing is quiet almost by definition — it happens during the day, with no upstairs neighbour walking around and no traffic rush outside. Sound insulation is one of the easiest things to misjudge in the fifteen minutes you spend in a property, because the noise that will actually bother you only shows up once someone is living there.
Why it happens. Many older Spanish apartment buildings were built with solid but acoustically simple floor slabs and party walls, without the resilient underlayment or acoustic insulation that newer construction standards require, so footsteps and voices from neighbouring flats and even plumbing noise from shared risers can travel more than expected. Single-glazed or poorly sealed windows add street and traffic noise on top of that, especially on lower floors or busy streets.
Why it matters. Impact noise from footsteps above, pipes running behind a bedroom wall, or traffic outside a bedroom window is the kind of thing that's tolerable for a week and genuinely wearing after a year — it affects sleep, concentration, and how livable a home feels, and it's very difficult and expensive to fix retroactively once you own the property.
How it's checked. An inspector assesses window glazing type and seal condition, checks party wall and floor construction where visible or documented, and notes proximity to likely noise sources — busy streets, lifts, shared risers, neighbouring terraces — to flag where acoustic performance is likely to fall short, since a full acoustic test requires specialist equipment beyond a standard inspection.
Unshaded West- or South-Facing Glazing That Turns a Room Into an Oven Every Afternoon
Large windows and a bright, sunny room are exactly what most buyers are looking for — and on a viewing, that sunlight reads as a selling point. What it doesn't show is what the same room feels like on a still August afternoon with the sun hitting unshaded glass for hours.
Why it happens. West- and south-facing rooms with large single- or standard double-glazed windows and no external shading — shutters, awnings, a covered terrace, or even deep-set reveals — absorb solar heat through the day and release it well into the evening, especially on upper floors, and this effect is easy to miss on a viewing scheduled in the morning or on a cloudy day.
Why it matters. In summer, a room like this can become genuinely uncomfortable to spend time in — noticeably hotter than the rest of the home — and forces heavy reliance on air conditioning to compensate, which pushes up electricity costs and puts extra load on a cooling system that, per the earlier point, may already be undersized for the room.
How it's checked. An inspector notes window orientation, glazing type and the presence or absence of external shading, and factors solar exposure into the assessment of whether the installed air-conditioning capacity is realistically adequate for that room, rather than treating orientation as a cosmetic detail.
Why These Issues Are So Easy to Miss
All seven share the same pattern: nothing about them is visible, and none of them show up on a short viewing. Water comes out of the tap, the AC switches on, the radiators warm up, the extractor grille is in place, the shower drains, the room feels bright and quiet — from a buyer's point of view, everything checks out. This is exactly why a pre-purchase inspection isn't a visual walk-through — it's instrument-based verification of the property's systems: measuring water flow and pressure under simultaneous demand, timing how fast a shower tray actually drains, matching AC and heating capacity to the real room load, measuring real extraction performance rather than assuming it from a switch, and assessing window orientation, shading and glazing rather than just how sunny a room looks on the day of the viewing. This kind of check matters even more for buyers unfamiliar with Spanish building conventions and older housing stock — where the cost of finding out after completion is far higher than the cost of the inspection itself.
Frequently Asked Questions
Can I spot these issues myself during a viewing?
Partially. It's worth asking to run two taps at once and listening for whether the extractor sounds like it's straining. But properly sizing an AC unit to the room, or measuring actual extractor airflow, needs equipment a buyer won't have on a viewing.
How expensive is it to fix these after purchase?
Replacing or upgrading an AC unit, reworking the water supply pipework, or installing proper mechanical ventilation all cost several times more than a pre-purchase inspection — and mean carrying out building work in a home you already live in.
Does a HouseDoctor inspection check HVAC performance?
Yes — heating, air conditioning and ventilation are inspected as their own category, with instrument-based capacity, temperature and airflow checks rather than a visual look only.
Does a HouseDoctor inspection check plumbing?
Yes — water supply and drainage are tested under real conditions: flow rate and pressure are measured at multiple fixtures at once, and drains are checked under sustained flow rather than a quick glance.
Does a HouseDoctor inspection check thermal and sound insulation?
Partially. Window orientation, glazing type, shading and party wall or floor construction are assessed as part of a standard inspection, but a full acoustic test needs specialist equipment beyond what a standard visit includes.
Before you buy, know what you're buying.