An empty Lisbon apartment needs a thorough check twice a month under normal conditions. In the wet season, add an extra check after heavy rain or a storm. Regular walkthroughs catch slow problems like creeping damp, mould and evaporating drain traps before they turn into costly repairs.

How often to check

Wet season (October to March)

Recommended frequency: Twice a month, plus an extra check after heavy rain or storms.
Main risks: High humidity, creeping mould, and water ingress.
Key checks: Humidity readings, airing based on hygrometer data, and targeted leak checks.

Drier months (April to September)

Recommended frequency: Twice a month.
Main risks: Evaporating drain traps, sewer odours, and extreme heat.
Key checks: Water-line and drain-trap refreshes, along with general property walkthroughs.

What a check every two weeks does well

Most problems in an empty home are slow ones: humidity creeping up, condensation on cold walls and windows, mould starting in a corner, a damp patch spreading, stale air, a letterbox filling with post. These build over days and weeks, so a regular visit catches them while they are still small, easier and cheaper to solve.

What it can't catch

Fast problems. A burst pipe or a failed hose can flood an apartment within a day, and no visit schedule prevents that.

Why the wet season is different in Lisbon

Lisbon's rain falls mostly between October and March, and the air stays humid. Nobody is there to heat or ventilate an empty apartment, so that damp air settles in, and condensation or a small leak can go unnoticed.

Climate & Humidity

Lisbon’s wet season runs from October to March, accounting for roughly three-quarters of the city's annual rainfall, about 550 of 720 mm, according to IPMA climate data. Morning outdoor humidity frequently reaches 83-86% according to IPMA 1971–2000 climate normals, meaning unheated, unventilated apartments naturally trap moisture over time.

Average Monthly Rainfall in Lisbon (mm)

Average Morning Relative Humidity in Lisbon at 9:00 AM (%)

The winter of 2026 was an extreme example. Storms Kristin, Leonardo and Marta caused widespread flooding across the Iberian Peninsula, including along the Tagus (Tejo) river region north-east of Lisbon (European Space Agency). Any damage left unrepaired after last winter's storms can leave roofs, terraces and window frames vulnerable to water ingress when heavy rain returns.

Healthy humidity level indoors

Official building standards in Portugal recommend keeping indoor relative humidity between 30% and 70%, with a tighter comfort window of 40% to 60% preferred (LNEC Guia de Apoio / Indoor Air Quality Guidelines). When humidity climbs past 75% in unventilated rooms, surface condensation allows mould to take hold rapidly on cold walls and behind furniture.

In an empty, unheated apartment, indoor humidity tends to follow the outdoor air, so it can easily sit above that target for weeks.

What a thorough walkthrough of your home should include

A walkthrough is more than a look around. Ours covers:

Reading the humidity and airing the apartment according to the reading, not a fixed routine
Mould monitoring
Checking for leaks and signs of water coming in
Refreshing the water lines and drain traps, so traps stay full and sewer smells stay out
Checking the rest of the property for visible problems
Collecting and sorting the post
Sending the owner a photo report after every visit

The photos matter more than they seem. A dated record shows when a problem first appeared, which helps with repairs, with the condominium and with insurance.

A small sign of a bigger problem

In one apartment we noticed the paint bubbling on a wall above the TV, about 1.5 metres below an air conditioning unit. It looked cosmetic. But bubbling paint means moisture is reaching the wall, and the place where it shows is rarely where the water gets in. Finding it at a routine visit, with a dated photo, means the source can be traced before paint, plaster and furniture are damaged.

Before you leave

The essentials:

Close the main water valve and the gas valve, and switch off an electric water heater (a termoacumulador) if the water is off.
Give the building administrator and a neighbour your contact details, and tell them who will be checking the apartment.
Leave a spare key with someone you trust, along with a note of who can authorise urgent repairs if you can't be reached.
Check what your home insurance policy says about unoccupied properties.