Winter guide
In most Portuguese homes the cause is the same: uninsulated walls and ceilings, where water vapour from the house cools down and condenses. If you moved here from a colder country, the first winter can come as a surprise. Here is how to tell where the damp comes from and what actually helps.
By David Francisco, civil engineer at EnergyEase · Published 16 October 2026
Sound familiar?
“Work done to solve a condensation problem. Now the critical time has come, with lower temperatures, there is no trace of it.”
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Cold or mouldy home?
At the visit we look at the walls, the cavity and the attic, and tell you what is worth insulating. Written quote usually within 48 h.
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Free technical visit
with an inspection camera
We tell you what we do not fix
leaks come first
Written quote
usually within 48 h
Why it happens
Many homes were built for a mild climate, without central heating and without insulation rules: Portugal's first thermal regulation for buildings only came in 1990. In winter, the outside walls get cold on the inside, and that is where the moisture in the house turns back into water.
Where does the damp come from?
From everyday life. In a family of four that dries laundry indoors, it can add up to about 15 litres of water a day in the air of the house, without noticing.
Showering
about 0.2 L per person per day
Cooking
2 to 3 L a day
Drying laundry indoors
about 1.5 L per person per day
Sleeping and breathing
about 0.3 L per person per night
Indicative figures from a PhD thesis at the University of Porto, FEUP (Amaral, 2008), based on data from LNEC, Portugal's national civil engineering laboratory. The total for four people is our own calculation.
The same home in winter: without and with insulation
Without insulation
The wall stays cold on the inside
With insulation
The cavity filled with mineral wool
Filling the cavity costs €25–45/m² incl. VAT and takes 1 to 3 days in a typical house.
Blown-in insulation →15.7%
of people in Portugal could not keep their home adequately warm in 2024. The EU average was 9.2%.
9 in 10
energy certificates for Greater Lisbon homes built between 1961 and 2000 record no wall insulation.
EnergyEase analysis of SCE (ADENE) data, February 2026
1990
is the year of Portugal's first thermal regulation for buildings. Before that, insulation was not required.
Decree-Law 40/90 (RCCTE)
18 °C
is the minimum indoor temperature the World Health Organization recommends in cold weather.
Certificates record what the assessor can verify. Some walls may have insulation that was not recorded.
Diagnosis
On the wall, all three look alike. But the causes and fixes are different, and insulation only helps with the first.
Here insulation helps
Insulation helps: the wall gets less cold and the risk goes down.
Fix it first
Insulation does not fix it. Deal with it first.
Needs another treatment
Insulation does not fix it. Deal with it first.
Based on the DECO PROteste guide to types of damp in the home (in Portuguese).
A simple test
The aluminium foil test
Tape a square of aluminium foil over the stain, sealed all round, and wait about 48 hours.
Moisture on the room side of the foil: condensation, from the air in the house. Moisture on the wall side: water is coming from inside the wall, from a leak or from the ground.
It gives an indication, not a diagnosis. At the visit we look at the wall and, if needed, inside it with a camera.
Not sure which one you have?
At the free visit we look at the wall, the cavity and the attic, and tell you where the damp comes from before we quote.
Ventilation
Insulation makes the walls less cold, but it does not remove vapour from the house: vapour only leaves when the air is renewed. That is why the World Health Organization recommends that insulation always goes with good ventilation. If you also replace the windows with more airtight ones, airing matters even more.
Open wide, for a short time
Windows fully open for 5 to 10 minutes, 2 to 3 times a day. When it is cold or windy the air changes faster, and 5 minutes is enough.
Create a draught
Open windows on opposite sides of the house, not side by side, and leave the inside doors open. Then 3 to 5 minutes is enough.
Air right when there is vapour
The bedroom when you get up. The bathroom and kitchen during and right after a shower or cooking, with the door closed so the vapour does not spread through the house.
Do not leave windows ajar for hours
It renews little air, wastes a lot of heat and cools the wall around the window, which is exactly where condensation then forms.
Switch the heater off while you air
In a few minutes the air goes out, but the walls and furniture keep their heat. Once you close the window, the house warms up again quickly.
Remove vapour where it starts
Cooker hood on and lids on pans. Laundry dried outside or in a well-aired room with the door closed.
Let the air move
Do not block the vents, and keep furniture a few centimetres away from outside walls.
Based on the heating guide from ADENE / Save Energy Together (in Portuguese) and the German Environment Agency (in German).
What about a dehumidifier?
It treats the symptom, not the cause
It takes water out of the air and helps on very humid days. But it does not renew the air or warm a cold wall: when you switch it off, the damp comes back.
The cause is dealt with by fresh air every day and, if the wall is cold, by insulation.
Advice based on DECO PROteste (in Portuguese) and the WHO guidelines.
When the mould keeps coming back
If you air the house and the mould keeps coming back in the same place, that wall or ceiling is too cold. Insulation makes those surfaces less cold on the inside and lowers the risk of condensation. Where to start depends on the house.
Top floor or house
Often the cheapest
€25–45/m²
Attic floor. Above an existing false ceiling: €35–70/m²
Worth it if
On the top floor, the ceiling is the largest surface exposed to the cold. It is often the first step.
Attic insulation →
Walls with a cavity
Done in 1 to 3 days
€25–45/m²
Mineral wool blown into the cavity through small holes we close afterwards
Worth it if
It does not insulate pillars and beams, where the wall has no cavity. If the mould shows there, we talk about capoto or a lining wall.
Blown-in insulation →
No cavity, or stone
One room or the whole façade
€70–200/m²
Capoto €70–130/m², insulated lining wall €80–200/m²
Worth it if
A lining wall goes room by room, but takes a few centimetres. Capoto also covers pillars and beams; in a building it needs condominium approval.
Wall insulation →Prices incl. VAT, from projects completed in 2025 and 2026. The final price is the one in the written quote, after the visit. Compare the options →
The technical visit
We look at where the stains are and on which walls. We measure the areas and, through a small hole, check with a camera whether the wall has a cavity and what state it is in.
If the damp comes from a leak, the roof or the ground, we tell you. Insulating a wet wall does not fix it: first deal with the cause, then insulate.
What we do not do
“Four months after we insulated the walls and the attic, the thermal comfort in the house has improved a lot. […]”
Mario C. · Google, translated from Portuguese
“[…] only took a day to complete. […] It has made a big difference to internal temperatures during cold spells.”
LM W. · Google review
“[…] 4 windows […] collected water from condensation on the inner frames, until it completely soaked the plasterboard of the wall. With Energyease's solution (cork + gypsum boards), the problem was solved.”
Eduardo N. · Google, translated from Portuguese
How it works
Today
Request
Fill in the form or call us. We arrange the visit.
Free
Technical visit
We look at the stains, the walls, the cavity and the attic.
Usually within 48 h
Written quote
With the final price incl. VAT and what to insulate first.
When you decide
Work
Blown-in insulation is done in 1 to 3 days in a typical house.
At the free visit we find out where the damp comes from and what is worth insulating. If it is a leak, we tell you. The written quote usually follows within 48 hours.
FAQ
Another question? Call us on 210 270 937 or message us on WhatsApp.
If the patch is small (up to half a square metre) and only on the surface, you can clean it: wearing gloves and a mask, with the window open, wipe it with 70% alcohol or a mould remover and let it dry. Larger patches, or mould (mold) that has gone into the wall, need a professional, and people with allergies or breathing problems should not clean it themselves. Cleaning is not enough: if the wall stays cold and the air damp, the mould comes back in the same place. Air the house every day, move furniture away from outside walls and check whether it is condensation or a leak. If it keeps coming back on a cold wall, insulating that wall or the ceiling lowers the risk. Cleaning advice based on the German Environment Agency.
Condensation shows in corners, around windows and behind furniture, and gets worse on cold days. A leak leaves yellowish stains that get worse after rain. The aluminium foil test gives an indication: moisture on the room side of the foil is condensation; on the wall side, the water comes from the wall.
Open the windows every day, wide and for a short time, especially when you get up and after showering and cooking, and wipe off the water that collects on the glass and frame. Single glazing and aluminium frames without a thermal break are the coldest surfaces in the house, so water shows there first. New, more airtight windows cut draughts but also fresh air: after replacing them, airing matters even more.
In most Portuguese homes the walls and ceilings have no insulation: the first thermal regulation for buildings only came in 1990. Many homes also have no central heating. The house loses heat through the outside walls, the top-floor ceiling and the windows, and the surfaces stay cold on the inside.
On a sunny winter day it can be warmer outside at midday than indoors. Uninsulated walls stay cold and, without central heating, the house never warms up. Insulation helps the house keep the heat you put in.
It lowers the risk of condensation, because the walls are less cold on the inside. It is not a guarantee: the house still needs airing, and insulation does not fix leaks or rising damp, which must be dealt with first.
Parts of the wall that get colder than the rest: pillars, beams, slab edges, corners and roller-shutter boxes. That is where condensation and mould appear first. Blown-in insulation insulates the wall inside the cavity, but not the concrete pillars and beams; capoto, on the outside, covers those too. At the visit we show you where the thermal bridges in your home are and what each option solves.
No. It takes water out of the air and helps on very humid days, but it treats the symptom, not the cause: it does not renew the air or warm a cold wall. When you switch it off, the damp comes back. The cause is dealt with by airing every day and, if the wall is cold, by insulating it.
Yes. Insulation makes the walls less cold, but showers, cooking and breathing keep producing vapour, and it only leaves when the air is renewed. Open the windows every day and use the cooker hood and bathroom fan.
The mineral wool we blow in is water-repellent. But the wall must be sound: leaks or rising damp are dealt with before insulating. At the visit we check the state of the wall.
We photograph the wall before we start and at the end. During the work you can ask us at any time to look inside the wall together with the endoscope camera, and you can count the bags of wool that go into the wall.
Insulation is the owner's decision and, for the façade of a building, the condominium's. The tips on this page still help. If your landlord wants to look into it, we do the visit and the written quote free of charge.
On the top floor, with the attic or ceiling: the attic floor costs €25–45/m². If the walls have a cavity, blown-in insulation costs €25–45/m² and takes 1 to 3 days. You can also start with the coldest room, with an insulated lining wall.
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