Telling condensation, rising damp and leaks apart (humedades)

Terms used

• Condensación — Condensación is water that forms when warm, humid indoor air touches a cold surface.
• Humedad por capilaridad — Humedad por capilaridad is rising damp: groundwater climbing up porous walls that have no damp-proof barrier.
• Filtraciones — Filtraciones are leaks, where water enters from pipes, roofs, terraces, facades or neighbouring flats.
• Arquitecto técnico — An arquitecto técnico, also called aparejador, is a building technician who can give an independent written report.
• Seguro de hogar — Seguro de hogar is home insurance, which may cover sudden water damage.

Key rules

• Target humidity: Keep indoor humidity at 40–60% to lower the risk of mould.
• Cause first: Identify the cause before you buy equipment or paint, because each cause needs a different fix.
• Shared parts: A leak from a shared part of the building is the community's responsibility, not yours.
• Renters: If you rent, report damp to the landlord in writing and keep a copy.
• Independent report: For a dispute or a purchase, ask an arquitecto técnico for a written report rather than relying on a company that sells treatments.

The three causes in short

Most damp in Spanish homes is one of three things. Each looks different and needs a different fix, so find the cause before you spend money.

Condensación (condensation). Warm, humid indoor air meets a cold surface and turns into water. You see droplets and black mould on cold walls, in corners, around windows and behind furniture. It is worst in winter and in rooms with poor airflow.

Humedad por capilaridad (rising damp). Groundwater climbs through porous walls that have no damp-proof barrier. You see a tide line up to about 1 m high, white salts and peeling plaster. It mostly affects ground floors and basements.

Filtraciones (leaks). Water gets in from pipes, roofs, terraces, facades or a neighbour's flat. You see a stain in one place, tide marks or bubbling paint. It grows after rain or after you use water.

How to tell which one you have

The checklist below walks you through the tests. In short:

• Pattern. Mould in cold corners and around windows points to condensation. A low band with salts points to rising damp. One isolated, spreading stain points to a leak.
• Season. Worse in winter, whatever the weather outside, means condensation. Worse after rain means an external leak. Steady all year means rising damp or a leaking pipe.
• Humidity. A hygrometer shows the room's humidity. Aim for 40–60%. A reading that stays higher points to condensation.
• Foil test. Tape a square of aluminium foil to the wall for 24 to 48 hours. Water on the room side of the foil means condensation. Water under the foil means damp coming through the wall.
• Water meter. Close every tap. If the meter still moves, a pipe is leaking.

These checks are a first look, not a diagnosis. Damp can have more than one cause at once.

The fix for each cause

Condensation: change habits first.

• Ventilate across the home, use extractor fans and keep trickle vents open.
• Heat steadily rather than in bursts.
• Do not dry laundry indoors.
• Use a dehumidifier if the air stays damp.
• Clean mould with an anti-mould product.
• If it keeps returning, the wall may need insulation or a repair to a cold spot in the structure.

Rising damp: repair the building.

• Options include an injected chemical barrier (inyecciones), a physical damp-proof course, or drainage or a ventilated gap around the wall.
• Replace salt-laden plaster with breathable render.
• Results vary, and the source of the water must be dealt with too. A dehumidifier will not cure it.

Leaks: find and repair the source.

• The source may be a pipe, terrace waterproofing, roof, facade or window sealant.
• Only after that, dry the wall out and redecorate. Painting over a leak hides it for a few weeks.

The decision below helps you choose between habits, equipment and repair.

Who to call

• Arquitecto técnico or aparejador (building technician). Gives an independent diagnosis and a written report. This is the best choice for a dispute, a purchase or a fault that affects the whole building.
• Empresa de humedades (damp specialist). Diagnoses and treats, but may be selling its own treatment. Compare more than one quote.
• Fontanero (plumber) or leak-detection firm. Best for a suspected pipe leak. They use thermal cameras or gas tests.
• Waterproofing contractor. Suits roofs and terraces.
• Your seguro de hogar (home insurance). It may send a loss adjuster and cover sudden water damage. Report the damage quickly.

Cost

Prices depend on the professional, the size of the home, the tests used and whether you need a signed report. A company's quote is often free or cheap. An independent report from an arquitecto técnico usually costs more. A plumber usually charges a call-out fee plus the work. Get several quotes, and ask the local college of aparejadores or a few firms for current prices.

Who is responsible

If the leak comes from a shared part of the building, such as the roof, facade or main pipes, the community of owners is responsible for the repair. If you rent, tell the landlord in writing and keep a copy. The FAQ below covers insurance and shared-part costs.

Damp is more common in northern and rainy regions, on the Canary Islands, in older buildings, and on ground floors. Check for it before you rent or buy there.

Dehumidifier, ventilation or repair: which do you need?

Dehumidifier, ventilation or repair

Which fix does your damp need: changing habits, buying equipment or repairing the building?

• Change your habits: Water on windows, black mould in cold corners, worse in winter, and no sign of a leak. Ventilate 10–15 minutes a day, use the extractor hood when cooking, dry laundry outside the living space and heat moderately. This costs almost nothing.

• Add equipment: The damp is still there after a few weeks of better habits, or the home is closed up in winter. A basic bathroom fan costs tens of euros plus installation. A compressor dehumidifier (10–25 L a day) is mid-priced and draws roughly 200–450 W. A desiccant model costs more and draws roughly 300–700 W, but suits cold rooms. A small Peltier unit is cheapest at roughly 20–100 W, for small rooms only. A humidity meter shows whether it is working.

• Repair the building: There is a clear source: tide marks low on ground-floor walls, salts, peeling plaster, a leaking roof, pipe, façade or terrace, or damp that does not change after better ventilation. A dehumidifier will not fix these because the water keeps coming in. Ducted or heat-recovery ventilation runs from a few hundred to a few thousand euros. Ask an arquitecto técnico (a technical architect) to diagnose it first.

Start with habits for mild condensation. Move to equipment if it persists. Go straight to a technician for repair if you can see a source, if mould is severe or widespread, if there is structural damage, or if damp keeps returning to the same spot. In a rented home, tell the landlord in writing: structural causes are generally the landlord's job, and leaks from shared parts of the building are the community's.

Checklist

• Look at the pattern of the stains: black mould in cold corners and around windows points to condensation, a low band with salts points to rising damp, and one isolated spreading stain points to a leak.

• Note when it gets worse: in winter without any link to rain means condensation, after rain means an external leak, and all year round means rising damp or a pipe leak.

• Measure the room's humidity with a hygrometer, a small humidity meter: a reading that stays above about 60–70% points to condensation.

• Tape a square of aluminium foil to the wall for 24 to 48 hours, then check which side is wet: moisture on the room side means condensation, and moisture under the foil means damp coming from inside the wall.

• Close every tap, then watch the water meter: if it keeps moving, you have a pipe leak.

• Inspect the gutters, the sealant around windows and the flat above for signs of water.

• If the checks do not settle the cause, call the right professional: an arquitecto técnico for an independent report, a plumber for a pipe leak, or a waterproofing contractor for a roof or terrace.

These checks are a first look only and do not replace a professional diagnosis.

Frequently asked questions

Who should I call to diagnose damp in my home?

Call an arquitecto técnico (aparejador) or an arquitecto if you need an independent written report. A report helps in disputes, when buying, or for faults shared by the whole building. A plumber or leak-detection firm suits a suspected pipe leak, and a damp company diagnoses and treats but may sell its own remedy.

Does home insurance cover damp and leaks?

Home insurance (seguro de hogar) may cover sudden water damage, and the insurer may send a loss adjuster. Call your insurer as soon as you see a fresh leak. Slow damp from poor ventilation is a different case, so ask what your policy covers.

Who pays to fix a leak from a shared part of the building?

The community of owners is responsible for leaks from common elements such as the roof or facade. If you rent, tell your landlord in writing about any damp or leak. Keep a copy of the message.

How much does a damp diagnosis cost?

The price depends on who you hire, the size of the home, the tests used and whether you need a signed report. A company's quote is often free or low-cost, and an independent technical report usually costs more.