Damp, mould and pests

It is for anyone considering, planning or carrying out a move to Spain. You will be able to tell damp types apart, keep mould away and handle the pests you are most likely to meet.

Start with "Telling condensation, rising damp and leaks apart (humedades)". It shows you how to find the cause of a stain, and the right fix depends on the cause. If you are still viewing homes, "Spotting damp and leaks during a viewing" covers what to look for before you commit. Who pays for repairs in a rental is covered under renting, not here.

Key rules

• Target humidity: Keep indoor relative humidity at about 40–60%, since mould risk rises when it stays above about 60–70%.
• DIY mould limit: Clean mould yourself only on patches under about 1 square metre; larger areas, mould that keeps returning or mould inside walls need a professional.
• Radon level: The reference level for yearly average indoor radon is 300 Bq/m3, and private owners of existing homes have no duty to test.
• Daily airing: Air every home for about 10 minutes a day, even in winter, ideally with windows open on opposite sides.
• Cause first: Identify the cause before you buy equipment or paint, because each cause needs a different fix.
• Walk away: Visible damp or mould with no clear fix is a good reason to reject the home before signing.

Damp, mould and pests: the whole process, step by step

• Check the viewing for stains, smells and fresh paint (Spotting damp and leaks during a viewing): At the viewing, before you make an offer or sign

• Ask for the building's inspection report (ITE or IEE), which records damp and leak defects in common areas (Spotting damp and leaks during a viewing): Before you commit to buy or rent; ask the seller, the administrator or the community president

• Work out whether the damp is condensation, rising damp or a leak (Telling condensation, rising damp and leaks apart): As soon as you see a stain or mould, before choosing a fix

• Clean mould and treat its cause (Removing mould (moho) and stopping it coming back): After you know the cause; call a professional if the patch is large or keeps returning

• Build the airing routine into daily life (Airing, drying laundry and dehumidifiers the Spanish way): Every day, about 10 minutes, even in winter

• Deal with any infestation (Dealing with cockroaches, termites and woodworm (carcoma)): As soon as you spot signs; call a professional if it spreads

• Test for radon if you live on a ground floor or in a basement (Radon and indoor air quality at home): Leave a passive detector in place for 2 to 3 months, or ideally a year, then send it to a laboratory

Documents you may need

• The building inspection report — Spotting damp and leaks during a viewing

Damp, mould and pests: questions that cross several articles

Can I ask to see the building's inspection report before buying or renting?

Yes, the community of owners holds the report, and a buyer can ask the seller to get it. It records damp and leak defects in common parts such as roof, facade and plumbing, but not the inside of individual flats. Read Spotting damp and leaks during a viewing, then use your own checks inside the flat.

Does fresh paint on a wall mean the damp has been hidden?

Fresh paint on one wall or ceiling patch in an otherwise worn home is a warning sign. Move furniture, tap walls for a hollow sound and check the ceiling below an upstairs bathroom. Read Spotting damp and leaks during a viewing, then Telling condensation, rising damp and leaks apart to work out the cause.

How do I know whether black mould comes from condensation or from a leak?

Black mould in corners, around windows and behind furniture usually means condensation, while a stain that grows after rain or water use points to a leak. A tide line up to about 1 m from the floor suggests rising damp. Read Telling condensation, rising damp and leaks apart, then Removing mould (moho) and stopping it coming back.

Is it safe to use a butane or paraffin heater to dry a damp room?

No, these heaters have no flue, add water vapour to the room (butane gives roughly one litre of water per kilo burned) and can cause carbon monoxide poisoning in closed rooms. Braseros are the most dangerous. Read Airing, drying laundry and dehumidifiers the Spanish way for safer ways to keep a home dry.